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Conservation agriculture can provide a low-cost competitive option to mitigate global warming with reduction or elimination of soil tillage and increase soil organic carbon (SOC). Most studies have evaluated the impact of zero till (ZT) only on surface soil layers (down to 30 cm), and few studies have been performed on the potential for C accumulation in deeper layers (0–100 cm) of tropical and subtropical soils. In order to determine whether the change from conventional tillage (CT) to ZT has induced a net gain in SOC, three long-term experiments (15–26 years) on free-draining Ferralsols in the subtropical region of South Brazil were sampled and the SOC stocks to 30 and 100 cm calculated on an equivalent soil mass basis. In rotations containing intercropped or cover-crop legumes, there were significant accumulations of SOC in ZT soils varying from 5 to 8 Mg ha−1 in comparison with CT management, equivalent to annual soil C accumulation rates of between 0.04 and 0.88 Mg ha−1. However, the potential for soil C accumulation was considerably increased (varying from 0.48 to 1.53 Mg ha−1 yr−1) when considering the soil profile down to 100 cm depth. On average the estimate of soil C accumulation to 100 cm depth was 59% greater than that for soil C accumulated to 30 cm. These findings suggest that increasing sampling depth from 30 cm (as presently recommended by the IPCC) to 100 cm, may increase substantially the estimates of potential CO2 mitigation induced by the change from CT to ZT on the free-draining Ferralsols of the tropics and subtropics. It was evident that that legumes which contributed a net input of biologically fixed N played an important role in promoting soil C accumulation in these soils under ZT, perhaps due to a slow-release of N from decaying surface residues/roots which favored maize root growth.

It has been shown that cover crops can enhance soil nitrous oxide (N2O) emissions, but the magnitude of increase depends on the quantity and quality of the crop residues. Therefore, this study aimed to evaluate the effect of long-term (19 and 21 years) no-till maize crop rotations including grass [black oat (Avena strigosa Schreb)] and legume cover crops [vetch (Vigna sativa L.), cowpea (Vigna unguiculata L. Walp), pigeon pea (Cajanus cajan L. Millsp.) and lablab (Dolichos lablab)] on annual soil N2O emissions in a subtropical Acrisol in Southern Brazil. Greater soil N2O emissions were observed in the first 45 days after the cover crop residue management in all crop rotations, varying from � 20.2 � 1.9 to 163.9 � 24.3 m gNm � 2 h � 1 . Legumebased crop rotations had the largest cumulative emissions in this period, which were directly related to the quantity of N (r 2 =0 .60, p= 0.13) and inversely related to the lignin:N ratio (r 2 =0 .89, p= 0.01) of the cover crop residues. After this period, the mean fluxes were smaller and were closely related to the total soil N stocks (r 2 =0 .96,p = 0.002). The annual soil N2O emission represented 0.39–0.75% of the total N added by the legume

O N é um dos nutrientes demandados em maior quantidade pela cultura do milho e o seu suprimento adequado tem implicações técnicas, quanto ao desempenho e à lucratividade da cultura, e ambientais pelo alto potencial de lixiviação do nitrato. Resultados de 61 experimentos, realizados por 13 anos, numa parceria entre a Fundação Agrária de Pesquisa Agropecuária (FAPA) e a Universidade Federal do Rio Grande do Sul (UFRGS), foram analisados e interpretados visando o desenvolvimento de uma tecnologia de indicação de N para alto rendimento da cultura do milho em plantio direto e adaptado ao uso de plantas de cobertura na região centro-sul do Paraná. As quantidades de N (ureia) a serem aplicadas no milho foram estimadas a partir da demanda de N em diferentes faixas de rendimento de grãos da cultura (6–8, 8,1–10, 10,1–12 e 12,1–14 t ha–1), da disponibilidade de N à cultura em solos com diferentes teores de matéria orgânica (MO) na camada de 0–10 cm (< 40, 40–60 e > 60 g kg-1), do efeito de plantas de cobertura (gramínea, leguminosa, consórcio gramínea-leguminosa e nabo forrageiro) na disponibilidade de N, e da eficiência do N mineral aplicado. As doses de N indicadas (DNI) tiveram boa relação com as doses de máxima eficiência econômica (DMEE) calculadas para condições distintas de MO no solo, planta de cobertura e expectativa de rendimento (DNI = 39 + 0,80 DMEE, R2 = 0,74, n = 20, p = 0,03), o que confirma a adequação das doses para a cultura na região. As doses também apresentaram boa relação com a indicação de N vigente nos Estados do RS e SC (DNI: PR = -14 + 1,06 RS/SC, R2 = 0,88, n = 12, p = 0,02), o que valida o uso da indicação do centro-sul do PR, que apresenta expectativas de rendimento mais elevadas, para sub-regiões do RS/SC que apresentam alto potencial de rendimento da cultura. Da mesma forma, a indicação do RS/SC pode ser utilizada para subregiões do PR que apresentam menor aptidão climática à cultura do milho. Nitrogen (N) is required in large quantities by corn and its supply causes technical concerns related to crop performance and profitability, and environmental concerns in view of the high risk of nitrate leaching. Results of 61 field experiments conducted through 13 years, in a cooperative effort of the Fundação Agrária de Pesquisa Agropecuária (FAPA) and the Universidade Federal do Rio Grande do Sul (UFRGS), were analyzed and interpreted aiming at establishing a N fertilizer indication for high corn yields, adjusted to the use of winter cover crops in no-till soils in the South-Central region of Parana, Brazil. The urea-N rates were calculated based on the N required for different corn yield levels (6–8, 8.1–10, 10.1–12 and 12.1– 14 t ha-1) and taking into account the N availability in soils with different soil organic matter contents in the layer 0–10 cm (< 40, 40–60 and > 60 g kg-1), the effect of winter cover crops (grass, leguminous, grass-legume consortium, and wild radish) on N availability, and the efficiency of N fertilizer. The indicated rates of urea-N were closely related to the N rates for maximum economic efficiency (MEE) for different soil OM contents, cover crop and corn yield (N indication = 39+0.80MEE, R2 =0.74, n=20, p=0.03) corroborating the adequacy of this N indication for corn. The N rates were closely correlated with the rates recommended in the states of Rio Grande do Sul (RS) and Santa Catarina (SC) (Indication PR = -14+1.06 RS/ SC, R2 = 0.88, n=12, p=0.02). This confirms the use of the indication of Central South Parana for subregions of RS and SC with high corn yield potential. Likewise, the recommendation for RS and SC can also be used in subregions in PR that are climatically less suitable for corn.

The potential of conservation management systems to ameliorate degraded agricultural soils and mitigate global warming is related to their potential for long-term stabilization of soil organic matter (SOM). This study was performed in a 19-yr-old experiment that was set up on a degraded Paleudult (220 g kg -1 clay) in southern Brazil to (i) evaluate the effect of seven no-till crop rotations (grass- and legume-based cover crop systems) and mineral N fertilization (0 and 145 kg ha yr -1 ) on soil organic C (SOC) stocks (0-17.5-cm depth) and (ii) estimate rates of SOM dynamics in these systems under subtropical climate conditions. Annual C input (shoot + root) ranged from 2.61 to 7.84 Mg ha -1 with the highest values in legume-based and N-fertilized cropping systems. The SOC stocks were closely related to C input levels, and a minimum C input of 4.05 Mg ha yr -1 was estimated to maintain the original SOC stock of 31.38 Mg ha -1 Based on the one-compartment model of SOM dynamics, the SOM decomposition rate was estimated to be 1.2% and the humification coefficient was estimated to be 9.6%. After 19 yr, the stock of the original SOC decreased to about 24.78 Mg ha -1 , while accumulation of SOC derived from the crops ranged from 4.26 to 12.79 Mg ha -1 Our results highlighted the benefits of legume cover crop species in no-till systems for the stabilization of SOC in degraded agricultural soils.

The effects of organic amendments (10 and 50 g/kg soil of yard waste, yard + municipal waste, GreenEdge, and synthetic humic acid) on soil chemical properties related to aluminum (Al) phytotoxicity and nutrient availability were evaluated. Compost amendment increased Mehlich 3-extractable calcium (Ca), magnesium (Mg), phosphorus (P), and potassium (K) in the soil by 3.5-260 times. No significant effect of composts on total Al in solution was observed. Organic amendments increased solution pH and decreased the activities of phytotoxic Al species to less than the critical levels, as a result of the formation of aluminate and humic acid-Al complexes. Low-molecular-weight organic acids were not effective in forming complexes with Al. Application of composts increased the concentra- tions of most nutrients in soil solution, suggesting a potential for ameliorating subsoil, but care must be taken to avoid nitrogen (N) and P leaching. Amending composts to acidic soils appears a useful strategy for diminishing Al phytotoxicity potential and improving soil fertility.

The long‐term (8‐year) effects of summer (Mucuna spp.) and winter cover crops (Avena strigosa + Vicia sativa and Lolium multiflorum + Vicia sativa) in maize‐based cropping systems on the total, particulate, and mineral‐associated soil carbon (C) stocks in the 0‐ to 0.2‐m layer of a no‐till South Brazilian Acrisol (87 g kg−1 clay) were evaluated. Annual C sequestration rates and the carbon management index (CMI) were calculated taking a fallow/maize (F/M) system as reference. A greater average C sequestration rate (0.68 Mg ha−1 yr−1) and greater C lability (particulate C/mineral‐associated C) were observed in the soil under the Mucuna system, and this was related to the higher biomass input in comparison to the winter cover crop systems. These cropping system effects on amount and lability of soil C were summarized through the CMI. The results highlight the potential of C retention in soils under warm and humid subtropical climate through the adoption of high C input summer cover crops in no‐till productio...

Submitted by Guilherme Lemeszenski (guilherme@nead.unesp.br) on 2013-08-22T18:46:11Z No. of bitstreams: 1 S0100-06832009000200010.pdf: 469831 bytes, checksum: 70996d6064238ed16f1f3af4bced5d9d (MD5) Made available in DSpace on 2013-08-22T18:46:11Z (GMT). No. of bitstreams: 1 S0100-06832009000200010.pdf: 469831 bytes, checksum: 70996d6064238ed16f1f3af4bced5d9d (MD5) Previous issue date: 2009-04-01 Made available in DSpace on 2013-09-30T19:35:23Z (GMT). No. of bitstreams: 2 S0100-06832009000200010.pdf: 469831 bytes, checksum: 70996d6064238ed16f1f3af4bced5d9d (MD5) S0100-06832009000200010.pdf.txt: 42522 bytes, checksum: 680db5c81e43e12d12d544807ba55b8d (MD5) Previous issue date: 2009-04-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T15:09:32Z No. of bitstreams: 2 S0100-06832009000200010.pdf: 469831 bytes, checksum: 70996d6064238ed16f1f3af4bced5d9d (MD5) S0100-06832009000200010.pdf.txt: 42522 bytes, checksum: 680db5c81e43e12d12d544807ba55b8d (MD5) Made available in DSpace on 2014-05-20T15:09:32Z (GMT). No. of bitstreams: 2 S0100-06832009000200010.pdf: 469831 bytes, checksum: 70996d6064238ed16f1f3af4bced5d9d (MD5) S0100-06832009000200010.pdf.txt: 42522 bytes, checksum: 680db5c81e43e12d12d544807ba55b8d (MD5) Previous issue date: 2009-04-01 Os solos agrícolas podem atuar como dreno ou fonte de C atmosférico, dependendo do sistema de manejo adotado. Este estudo foi desenvolvido em experimento de longa duração (22 anos), durante o período de 30 dias do outono, com o objetivo de avaliar o impacto de sistemas de preparo de solo (preparo convencional-PC e plantio direto-PD) nas emissões de C-CO2 de um Latossolo Vermelho distrófico, em Cruz Alta, RS. As emissões de C-CO2 do solo foram avaliadas com câmaras dinâmica (Flux Chamber 6400-09, Licor) e estática (com captação em solução alcalina), imediatamente após a colheita da soja. A temperatura e a umidade do solo foram registradas, concomitantemente com as emissões de C-CO2, por meio de sensor de temperatura e TDR manual, respectivamente, integrantes do Licor-6400. Estimou-se que, em 30 dias, uma quantidade equivalente a menos de 30 % do C aportado pelos resíduos de soja foi emitida na forma de C-CO2. As emissões de C-CO2 no solo em PD foram similares às emissões do solo em PC, independentemente do tipo de câmara utilizada. Diferenças entre sistemas de preparo quanto à emissão de C-CO2, avaliadas com a câmara dinâmica, foram verificadas somente a curto prazo (leituras diárias), com o PD apresentando maiores emissões do que o PC no início do período experimental e menores no final. A câmara dinâmica foi mais eficiente do que a estática em captar as alterações das emissões de C-CO2 em função da variação da temperatura e a porosidade preenchida por água (PPA) no solo em PD, as quais explicaram 83 e 62 % das emissões de C-CO2, respectivamente. O fator Q10, que avalia a sensibilidade da emissão de C-CO2 à temperatura do solo, foi estimado em 3,93, indicando alta sensibilidade da atividade microbiana à temperatura do solo durante o outono. As emissões de C-CO2 registradas no solo em PD com a câmara estática foram correlacionadas às da câmara dinâmica, porém com valores subestimados em relação àquela notadamente nos maiores valores de fluxo. em condições de baixa temperatura e PPA, o preparo de solo induziu limitado incremento de emissão de C-CO2. Agricultural soils can act as a source or sink of atmospheric C, according to the soil management. This long-term experiment (22 years) was evaluated during 30 days in autumn, to quantify the effect of tillage systems (conventional tillage-CT and no-till-NT) on the soil CO2-C flux in a Rhodic Hapludox in Rio Grande do Sul State, Southern Brazil. A closed-dynamic system (Flux Chamber 6400-09, Licor) and a static system (alkali absorption) were used to measure soil CO2-C flux immediately after soybean harvest. Soil temperature and soil moisture were measured simultaneously with CO2-C flux, by Licor-6400 soil temperature probe and manual TDR, respectively. During the entire month, a CO2-C emission of less than 30 % of the C input through soybean crop residues was estimated. In the mean of a 30 day period, the CO2-C flux in NT soil was similar to CT, independent of the chamber type used for measurements. Differences in tillage systems with dynamic chamber were verified only in short term (daily evaluation), where NT had higher CO2-C flux than CT at the beginning of the evaluation period and lower flux at the end. The dynamic chamber was more efficient than the static chamber in capturing variations in CO2-C flux as a function of abiotic factors. In this chamber, the soil temperature and the water-filled pore space (WFPS), in the NT soil, explained 83 and 62 % of CO2-C flux, respectively. The Q10 factor, which evaluates CO2-C flux dependence on soil temperature, was estimated as 3.93, suggesting a high sensitivity of the biological activity to changes in soil temperature during fall season. The CO2-C flux measured in a closed dynamic chamber was correlated with the static alkali adsorption chamber only in the NT system, although the values were underestimated in comparison to the other, particularly in the case of high flux values. At low soil temperature and WFPS conditions, soil tillage caused a limited increase in soil CO2-C flux. Universidade Federal do Rio Grande do Sul (UFRGS) PGCS Universidade Federal de Santa Maria (UFSM) Universidade Federal do Rio Grande do Sul (UFRGS) Universidade Estadual Paulista UFRGS PPGCS FUNDACEP UNICRUZ Universidade Estadual Paulista

Summary We examined the influence of land use change, tillage system and soil texture on organic carbon (C) stocks and on organic matter composition of tropical and subtropical soils from Brazil at four long-term experiments (11–25 years) based on fine- and coarse-textured soils. Soil samples were collected from the 0–5, 5–10 and 10–20 cm layers of conventional tillage (CT) and no-till (NT) plots, and of the adjoining soil under native vegetation (NV) of Cerrado (tropical) or grassland (subtropical). Conversion of NV to CT resulted in losses of 7–29% of the original C stock of 0–20 cm; conversion to NT increased this C stock by 0–12% compared with CT. Organic matter composition of the 0–5 cm layer, assessed by solid state CPMAS- 13 C-NMR, ESR and laser induced fluorescence spectroscopies, was affected by land use and tillage systems. Conversion of NV to CT decreased O-alkyl and increased aromatic, carbonyl, aromatic/O-alkyl ratio, free radicals concentration and fluorescence signal. The opposite trend was observed when NT replaced CT. The relative losses and gains of C and qualitative changes resulting from land use and tillage were less evident in fine- than in coarse-textured soils, suggesting a greater resistance and a smaller resilience of fine- compared with coarse-textured soils. The direct relation between increase in C stock and increase in potentially labile moieties (e.g. O-alkyl) and the decrease in more recalcitrant moieties (e.g. aromatics) in NT soils suggests that spatial inaccessibility by aggregates is playing a major role, compared with selective preservation, in promoting C accumulation in NT soils.

Addition of organic amendments can alleviate the level of aluminum (Al) phytotoxicity in acid soils by affecting the nature and quantity of Al species. This study evaluated the transformation of Al in an acidic sandy Alaquod soil amended with composts (10 and 50 g kg−1 soil of yard waste, yard + municipal waste, GreenEdge®, and synthetic humic acid) based on soil Al fractionation by single and sequential extractions. Though the organic compost amendments increased total Al in soil, they alleviated Al potential toxicity in acidic soil by increasing soil pH and converting exchangeable Al to organically bound and other noncrystalline fractions, stressing the benefits of amending composts to improve acid soil fertility. The single‐extraction method appears to be more reliable for exchangeable Al than sequential extraction because of the use of nonbuffered pH extract solution. Florida Agricultural Experiment Station – Indian River Research and Education Center Journal Series Number R‐100601.

O sistema plantio direto (SPD) altera a taxa dos processos que ocorrem no solo, porém pouco se conhece sobre sua influência na mineralogia de solos tropicais e subtropicais. Este estudo teve por objetivo avaliar o efeito do SPD na mineralogia dos óxidos de Fe pedogênicos e sua relação com a matéria orgânica do solo (MOS). Amostras de solos foram coletadas em 14 profundidades da camada superficial (0 a 0,20 m) de dois Latossolos sob SPD e sistema de preparo convencional (SPC), em áreas experimentais de longa duração, no sul do Brasil (Santo Ângelo, RS) e na região do Cerrado (Dourados, MS). A identificação mineralógica foi realizada por difração de raios X (DRX), sendo determinados os teores de Fe extraídos por DCB (Fed) e por oxalato de amônio (Feo) e os teores de carbono orgânico total (COT). Nos dois solos predominaram os minerais caulinita e hematita, e o SPD não afetou os teores médios de Fed, Feo, COT e a razão Feo/Fed na camada de 0–0,20 m, em comparação ao solo em SPC. Entretanto, no Latossolo subtropical (LVdf-1), com boa distribuição de chuvas durante o ano e temperaturas mais amenas, houve aumento dos teores de COT e da fração humina na camada superficial do solo (0–0,03 m) sob SPD. Ademais, essas variáveis apresentaram relação positiva com os teores de Feo e razão Feo/Fed. Contrariamente, no Latossolo tropical (LVdf-2), com concentração das chuvas no verão (outubro a março), não houve efeito do SPD na distribuição do COT e das frações húmicas no solo. Neste solo, os teores de Feo e da razão Feo/Fed apresentaram relação positiva com a profundidade do solo e negativa com os teores de COT e da fração humina. Provavelmente esses resultados são conseqüência do reordenamento dos óxidos de Fe, possivelmente a partir da dissolução redutiva da hematita e da maghemita nas camadas mais superficiais e da neoformação de óxidos de Fe de baixa cristalinidade nas camadas mais profundas. The no-tillage system (NT) affects the rate of soil processes, but little is known about its effect on the mineralogy of tropical and subtropical soils. This study aimed to evaluate the long-term effect of NT system on pedogenetic iron oxides and their relationship with soil organic matter (SOM) fractions. Soil samples were taken at 14 depths within the top 0,20 m soil layer from two clayey Oxisols under NT and conventional tillage (CT) systems of the experimental areas located near the counties of Santo Ângelo (RS State, Southern Brazil) and Dourados (MS State, Center-Western Brazil). The soil mineralogy was analyzed by X ray diffraction, and the contents of sodium dithionite-citrate-bicarbonate (Fed), ammonium oxalate (Feo) iron oxides, total organic carbon (TOC), and humic fractions were evaluated. Kaolinite and hematite were the predominant minerals in both soils, and the NT system had not effect on the mean concentration of Fed, Feo, TOC and the Feo/Fed ratio in the 0–0.20 m soil layer, in comparison with CT soil. However, in the soil in southern Brazil, under well-distributed annual rainfall and cooler temperatures in the winter, the TOC content and humine fraction in the surface layer (0–0.03 m) of NT soil were higher. These variables were also closely related with the Feo contents and Feo/Fed ratio. On the contrary, in the Oxisol under tropical conditions, with rainfall concentrated from October to March, no effect of the tillage system was observed on TOC and humic fractions of SOM contents. In this soil, the Feo content and Feo/Fed ratio were positively related to soil depth and negatively to TOC and humine contents. These results probably are a consequence of iron oxide rearrangements, possibly through the reductive dissolution of hematite and maghmite from soil surface layer, and neo-genesis of low crystalline iron oxides in the deeper soil layers.

The carbon management index (CMI) is derived from the total soil organic C pool and C lability and is useful to evaluate the capacity of management systems to promote soil quality. However, the CMI has not been commonly used for this purpose, possible due to some limitations of the 333 mM KMnO4-chemical oxidation method conventionally employed to determine the labile C fraction. We hypothesized, however, that physical fractionation of organic matter is an alternative approach to determine the labile C. The objectives of this study were (i) to assess the physical fractionation with density (NaI 1.8 Mg m−3) and particle-size separation (53 μm mesh) as alternative methods to the KMnO4-chemical oxidation (60 and 333 mM) in determining the labile C and thus the CMI, and (ii) to evaluate the capacity of long-term (19 years) no-till cropping systems (oat/maize: O/M, oat + vetch/maize: O + V/M, oat + vetch/maize + cowpea: O + V/M + C, and pigeon pea + maize: P + M) and N fertilization (0 and 180 kg N ha−1) to promote the soil quality of a Southern Brazilian Acrisol, using the CMI as the main assessment parameter. Soil samples were collected from 0 to 12.5 cm layer, and the soil of an adjacent native grassland was taken as reference. The mean annual C input of the cropping systems varied from 3.4 to 6.0 Mg ha−1 and the highest amounts occurred in legume-based cropping systems and N fertilized treatments. The C pool index was positively related to the annual C input (r2 = 0.93, P

Conservation management systems can improve soil organic matter stocks and contribute to atmospheric C mitigation. This study was carried out in a 18-year long-term experiment conducted on a subtropical Acrisol in Southern Brazil to assess the potential of tillage systems [conventional tillage (CT) and no-till (NT)], cropping systems [oat/maize (O/M), vetch/maize (V/M) and oat + vetch/maize + cowpea (OV/MC)] and N fertilization [0 kg N ha−1 year−1 (0 N) and 180 kg N ha−1 year−1 (180 N)] for mitigating atmospheric C. For that, the soil organic carbon (SOC) accumulation and the C equivalent (CE) costs of the investigated management systems were taken into account in comparison to the CT O/M 0 N used as reference system. No-till is known to produce a less oxidative environment than CT and resulted in SOC accumulation, mainly in the 0–5 cm soil layer, at rates related to the addition of crop residues, which were increased by legume cover crops and N fertilization. Considering the reference treatment, the SOC accumulation rates in the 0–20 cm layer varied from 0.09 to 0.34 Mg ha−1 year−1 in CT and from 0.19 to 0.65 Mg ha−1 year−1 in NT. However, the SOC accumulation rates peaked during the first years (5th to 9th) after the adoption of the management practices and decreased exponentially over time, indicating that conservation soil management was a short-term strategy for atmospheric C mitigation. On the other hand, when the CE costs of tillage operations were taken into account, the benefits of NT to C mitigation compared to CT were enhanced. When CE costs related to N-based fertilizers were taken into account, the increases in SOC accumulation due to N did not necessarily improve atmospheric C mitigation, although this does not diminish the agricultural and economic importance of inorganic N fertilization.

A avaliação da qualidade do solo (QS) é importante estratégia no planejamento agrícola, possibilitando a identificação e o aprimoramento de sistemas de manejo com características de alta produtividade e de preservação ambiental. O presente estudo foi realizado em dois experimentos de longa duração (10 e 15 anos) conduzidos no Sul do Brasil e teve por objetivo avaliar o efeito de sistemas de manejo na QS, utilizando um kit de análise expedita de qualidade de solo (KQS), desenvolvido pelo Instituto de Qualidade do Solo-USDA-ARS. A eficiência desse kit foi avaliada pela comparação com os métodos tradicionais utilizados na ciência do solo. Nas duas áreas experimentais investigou-se um total de 12 tratamentos, os quais englobaram sistemas de preparo com diferentes intensidades de revolvimento do solo (preparo convencional, preparo reduzido e plantio direto) e sistemas de culturas com ampla faixa de adição de resíduos vegetais ao solo, além da aplicação de doses anuais de N-uréia, variando de 0 a 144 kg ha-1. Em cada base experimental uma área sob campo natural foi avaliada, servindo como referência da condição do solo na ausência de interferência antrópica. Como indicadores de QS, foram avaliados infiltração de água, respiração do solo, densidade do solo, teor de nitrato+nitrito (N-NO3 - + N-NO2 -), estabilidade de agregados em água e pH. De maneira geral, os coeficientes de correlação entre os métodos do KQS e os métodos tradicionais foram elevados, sendo o mais alto para o indicador pH (r = 0,98) e o menor para o indicador infiltração de água no solo (r = 0,42). Os tratamentos selecionados foram teoricamente ordenados em ordem crescente de QS, a qual foi reproduzida de forma eficiente pelo índice de estoque de carbono (IEC), calculado pela razão entre o estoque de C orgânico do solo, na camada de 0-5 cm, de cada tratamento e o estoque de C orgânico no solo sob campo natural. Os indicadores estabilidade de agregados, N-NO3 - + N-NO2 - e respiração do solo foram os mais eficientes em discriminar a QS. O KQS foi eficiente em avaliar a QS dos tratamentos nas duas áreas experimentais. Os níveis mais elevados de QS foram alcançados nos tratamentos com plantio direto e consórcio de gramíneas e leguminosas tropicais, devido à cobertura do solo e às elevadas adições de C e N via resíduos culturais. The soil quality (SQ) evaluation is an important part of agricultural planning. It allows the identification and improvement of high-yielding management systems with characteristics of environment preservation. This study was carried out in two long-term soil management experiments (10 and 15 years) in Rio Grande do Sul State, Brazil. The main objective of this study was to evaluate the effectiveness of the Soil Quality Kit (SQK) developed by the Soil Quality Institute – ARS –USDA, compared to traditional soil science methods. Twelve treatments of cropping and tillage systems in a range of different tillage intensities, biomass input amounts and urea-N fertilization (0 to 144 kg ha-1) were evaluated. A native vegetation field close to each experimental area was sampled as reference treatment. The following SQ indicators: water infiltration, soil respiration, soil density, N-NO3 - + N-NO2 -, water aggregate stability and pH were evaluated. The correlation between the SQK and soil science methods was generally high. The highest correlation was observed with pH (r = 0.98) and the lowest for infiltration (r = 0.42). The soil management treatments were theoretically classified by crescent SQ order. The carbon pool index (CPI) was obtained dividing soil organic carbon stock of each treatment by native vegetation soil organic carbon 0 to 5 cm deep. The CPI reproduces the SQ classification efficiently. Aggregate stability, soil respiration and N-NO3 - + N-NO2 - were the most efficient indicators at discriminating SQ. The Soil Quality Test Kit was an efficient tool to evaluate the soil quality in both experimental areas. Highest soil quality levels were achieved under notillage with a grass - tropical legume consortium, which provides soil cover and high carbon and nitrogen addition through crop residues.

This study aimed to quantify the nitrous oxide (N 2 O) and methane (CH 4 ) fluxes at sites with different vegetation covers and where bird activity was present or absent using the static chamber method, on Rip Point, Nelson Island, maritime Antarctic. The sites were soils covered by Sanionia uncinata , lichens, Prasiola crispa , Deschampsia antarctica and bare soil. Seabirds used the P. crispa and D. antarctica sites as nesting areas. Soil mineral N contents, air and soil temperature and water-filled pore space were measured, and the content of total organic C and particulate organic C, total N, bulk density and texture were determined to identify controlling variables of the gas emissions. The N 2 O and CH 4 flux rates were low for all sampling events. Mean N 2 O flux rates ranged from 0.11±1.93 up to 21.25±22.14 µg N 2 O m −2 h −1 for the soils under lichen and P. crispa cover, respectively. For the CH 4 fluxes, only the P. crispa site showed a low positive mean (0.47±3.61 µg CH 4 m −2 h −1 ). The bare soil showed the greatest absorption of CH 4 (−11.92±5.7 µg CH 4 m −2 h −1 ), probably favoured by the coarse soil texture. Bare soil and S. uncinata sites had N 2 O accumulated emissions close to zero. Net CH 4 accumulated emission was observed only at the P. crispa site, which was correlated with ( p< 0.001). These results indicate that seabird activity influences N 2 O and CH 4 soil fluxes, while vegetation has little influence, and bare soil areas in maritime Antarctica could be greenhouse gas sinks. Keywords : Soil greenhouse gases; seabirds; vegetal cover; maritime Antarctica. (Published: 3 February 2015) Citation: Polar Research 2015, 34 , 23584, http://dx.doi.org/10.3402/polar.v34.23584

O Estado do Paraná não dispõe de um sistema de recomendação de adubação para rotação de culturas em plantio direto (PD). Em razão disso, utiliza indicações geradas para culturas individuais há mais de 30 anos e em preparo convencional. Este estudo teve como objetivo consolidar a calibração de P e avaliar a resposta das culturas à adubação fosfatada, visando à proposição de um sistema de indicações técnicas para a adubação fosfatada das culturas da soja, do milho, do trigo e da cevada cultivadas em sistema de rotação em Latossolos com longo histórico de PD (>30 anos) na região centro-sul do Paraná, que se caracteriza por possuir alto potencial produtivo. Três experimentos de calibração foram conduzidos de 2008 a 2013 e consistiram na criação de níveis de P pela aplicação de doses a lanço de até 640 kg ha-1 de P2O5. Quarenta e quatro experimentos de resposta a P foram conduzidos entre as safras de 2011 a 2012/13, tendo como foco avaliar a resposta das culturas a P em solos com distinta disponibilidade do nutriente. Os rendimentos relativos [RR = (rendimento sem P/rendimento máximo) × 100] das culturas e os teores de P no solo (Mehlich-1) foram relacionados, obtendo-se os teores críticos e as classes de disponibilidade de P no solo. Para a estimativa das doses nas classes de disponibilidade Baixa e Média, foram utilizadas as curvas de resposta à adubação de P, seguindo a filosofia de suficiência (adubação de cultura). Nas classes de disponibilidade Alta e Muito Alta, as doses foram com base na exportação pelos grãos. Os cereais de inverno se evidenciaram mais exigentes e determinaram o teor crítico de P de 8 mg dm-3 para a rotação de culturas, considerando a camada de 0-20 cm. As doses de P indicadas para soja, milho, trigo e cevada em solos em PD de longa duração são superiores às de adubação atualmente indicadas no PR, o que, ao menos em parte, justificam-se pelas altas produtividades das culturas e alta capacidade de retenção de P dos solos da região. Embora adotada a filosofia de suficiência/adubação de cultura para a indicação das doses de adubação fosfatada em solos abaixo do teor crítico, estima-se que as doses estipuladas para as culturas elevem o teor de P no solo ao teor crítico após um ciclo da rotação de culturas (três anos). Although the State of Parana, Brazil, has adopted crop rotation and no-till (NT) systems, fertilizer application is still based on recommendations developed more than 30 years ago for monocropping under conventional tillage because fertilizer recommendations developed specifically for crop rotation under NT are lacking. The objective of our study was to consolidate P calibration and evaluate crop responses to P fertilization so as to propose a system of technical recommendations for P fertilization for soybean, maize, wheat, and barley grown in a crop rotation system in Oxisols under long-term (>30 years) NT systems in the high yield potential South-Central region of Parana. Three calibration trials were conducted from 2008 to 2013, consisting of P broadcast application rates of up to 640 kg ha-1 P2O5. Forty-four P fertilization trials were carried out over the 2011-2012/13 growing seasons to evaluate yield response to P fertilization rates in Oxisols with different levels of P availability. Relative crop yield [RR = (yield without P/maximum yield) × 100] and soil P availability (Mehlich-1) were compared to obtain P critical levels and generate soil P availability classes based on crop response. For soils in the Low and Medium availability classes, recommended P fertilizer application rates were based on the yield response curve following the nutrient sufficiency approach. For soils in the High and Very High availability classes, P fertilizer recommendations were based on P removal through grain harvest. The winter cereal crops were more demanding to achieve maximum yields - the soil critical P level for the crop rotation system was determined at 8 mg dm-3 based on the requirement of these crops, considering the 0-20 cm soil layer. The recommended P fertilization rates for soybean, maize, wheat, and barley in Oxisols under long-term NT developed in our study are higher than the current P fertilization rates used in Parana, which is explained in part by the high crop yields and high P adsorption capacity of soils in the region. Although the nutrient sufficiency approach was used to determine P fertilization rates in the soils below the critical level, it is estimated that the P rates recommended for the crops will raise soil P availability above the critical level after a full crop-rotation cycle (3 years).

The one-compartment C model C t = C 0 e − k 2 t + k 1 A / k 2 ( 1 − e − k 2 t ) is being long used to simulate soil organic C (SOC) stocks. C t is the SOC stock at the time t ; C 0 , the initial SOC stock; k 2 , the annual rate of SOC loss (mainly mineralization and erosion); k 1 , the annual rate to which the added C is incorporated into SOC; and A , the annual C addition. The component C 0 e − k 2 t expresses the decay of C 0 and, for a time t , corresponds to the remains of C 0 ( C 0 remains ). The component k 1 A / k 2 ( 1 − e − k 2 t ) refers, at time t , to the stock of SOC derived from C crops ( C crop ). We herein propose a simple method to estimate k 1 and k 2 coefficients for tillage systems conducted in long-term experiments under several cropping systems with a wide range of annual C additions ( A ) and SOC stocks. We estimated k 1 and k 2 for conventional tillage (CT) and no-till (NT), which has been conducted under three cropping systems (oat/maize −O/M, vetch/maize −V/M and oat + vetch/maize + cowpea −OV/MC) and two N -urea rates (0 kg N ha −1 −0 N and 180 kg N ha −1 −180 N) in a long-term experiment established in a subtropical Acrisol with C 0 = 32.55 Mg C ha −1 in the 0–17.5 cm layer. A linear equation ( C t = a + bA ) between the SOC stocks measured at the 13th year (0–17.5 cm) and the mean annual C additions was fitted for CT and NT. This equation is equivalent to the equation of the model C t = C 0 e − k 2 t + k 1 A / k 2 ( 1 − e − k 2 t ) , so that a = C 0 e − k 2 t and b A = k 1 A / k 2 ( 1 − e − k 2 t ) . Such equivalences thus allow the calculation of k 1 and k 2 . NT soil had a lower rate of C loss ( k 2 = 0.019 year −1 ) than CT soil ( k 2 = 0.040 year −1 ), while k 1 was not affected by tillage (0.148 year −1 under CT and 0.146 year −1 under NT). Despite that only three treatments had lack of fit (LOFIT) value lower than the critical 5% F value, all treatments showed root mean square error (RMSE) lower than RMSE 95% indicating that simulated values fall within 95% confidence interval of the measurements. The estimated SOC stocks at steady state ( C e ) in the 0–17.5 cm layer ranged from 15.65 Mg ha −1 in CT O/M 0 N to 60.17 Mg ha −1 in NT OV/MC 180 N. The SOC half-life ( t 1/2 = ln 2/ k 2 ) was 36 years in NT and 17 years in CT, reflecting the slower C turnover in NT. The effects of NT on the SOC stocks relates to the maintenance of the initial C stocks (higher C 0 remais ), while increments in C crop are imparted mainly by crop additions.

Molecular recalcitrance and organomineral interaction are factors that determine soil organic matter (SOM) stability. This study was based on a medium-term (5 years) experiment located in southern Brazil and aimed (i) at investigating the influence of native grassland and two no-till cropping systems [bare soil and fallow/maize + mucuna ( Stizolobium cinereum )—F/M + Mu] over the C and N contents in the whole soil down to 17.5 cm depth and in the particle-size fractions (> 150, 150–53, 53–20, 20–2, and − 1 clay) and (ii) at assessing the role of molecular recalcitrance and organomineral interaction in stabilizing SOM in this subtropical soil. Molecular recalcitrance of SOM was inferred through the concentration of semiquinone free radicals, as assessed by ESR (electron spin resonance) spectroscopy. Semiquinone radicals are supposed to derive from and be stabilized by recalcitrant aromatic structures and are also believed to relate to the recalcitrance imparted by disordered structural conformation of humic substances. Organomineral interaction was assessed through power saturation experiments of ESR spectroscopy. Compared to grassland, the legume-based F/M + Mu system increased the C and N stocks of the 0–17.5 cm layer at rates of 0.40 Mg C ha − 1 year − 1 and 0.06 Mg N ha − 1 year − 1 . Losses of 0.80 Mg C ha − 1 year − 1 and 0.02 Mg N ha − 1 year − 1 were observed in bare soil. Only the fine silt (20–2 μm) and clay ( − 1 ) and N (2.95 to 4.34 g N kg − 1 ) concentrations, and the lowest C:N ratios (10.1 to 11.6). The concentration of semiquinone free radicals in physical fractions increased in the order F/M + Mu

A considerable proportion of the 200 million hectares of the Brazilian Cerrado is suitable for annual crops but little is known about the effects of tillage on the C dynamics of Cerrado soils. We evaluated the role of two representative Cerrado Oxisols (350 and 650 g clay kg−1) as sources or sinks of atmospheric C when managed under three tillage systems (conventional tillage (CT), reduced tillage (RT), and no-till (NT)) in 8- and 5-year long-term experiments. A literature review was also carried out and the mean C sequestration rates in no-till soils of tropical and subtropical regions of Brazil were calculated and compared with values for soils from temperate regions of the world. The original C stocks in 0–20 cm layer of soils under native Cerrado were higher in the clayey (54.0 Mg ha−1) than in the sandy clay loam soil (35.4 Mg ha−1), suggesting a higher physical stability of organic matter associated with variable clay minerals in the clayey Oxisol. The original C stocks of the native Cerrado soils appear not to have decreased after 23 years of conventional tillage in the sandy clay loam Oxisol, except when the soil had been subjected to erosion (15% loss of C), or after 25 years in the clayey Oxisol. Compared to conventionally tilled soil, the C stocks in no-till sandy clay loam Oxisol increased by 2.4 Mg ha−1 (C sequestration rate = 0.30 Mg ha−1 year−1) and in the clayey Oxisol by 3.0 Mg ha−1 (C sequestration rate = 0.60 Mg ha−1 year−1). The mean rate of C sequestration in the no-till Brazilian tropical soils was estimated to be 0.35 Mg ha−1 year−1, similar to the 0.34 Mg ha−1 year−1 reported for soils from temperate regions but lower than the 0.48 Mg ha−1 year−1 estimated for southern Brazilian subtropical soils. Considering the large area (about 70 million hectares) of the Cerrado which is currently used and potentially available for cropland, the adoption of no-till systems could turn the Cerrado soils into a significant sink for atmospheric C and contribute to the mitigation of global climate change.

Two Ferralsols (350 and 600 g kg−1 clay) from the Brazilian Cerrado Region were evaluated for long‐term effects (5 and 8 years) of no tillage on carbon (C) stocks in particulate (>53 µm) and mineral‐associated (

Fluorescence spectroscopy relies on the fluorescence emitted by rigid conjugated systems and thus can be used to assess the soil organic matter (SOM) humification. This technique is generally applied to solution samples of humic substances, and so far no information exists about its applicability to whole untreated soil samples. The laser-induced fluorescence (LIF) spectroscopy is proposed as a novel technique to assess the organic matter humification in whole soil samples. We sampled the 0- to 2.5-, 2.5- to 5-, 5- to 10-, 10- to 15-, and 15- to 20-cm layers of three Oxisols of long-term experiments located in two sites of the Brazilian Cerrado. The humification index based on LIF spectroscopy (H L I F ) of whole soil samples showed a dose correlation with the humification indexes A 4 /A 1 , I 4 6 5 /I 3 9 9 , and A 4 6 5 obtained after fluorescence spectroscopy analysis of the dissolved humic adds. The H L I F in soils under native cerrado or subjected to no-tillage increased from the top to the deepest layer, which is consistent with the deposition of labile organic matter from plant residues on the soil surface. The soils subjected to conventional tillage, however, showed relatively constant H L I F along the profile, possibly because homogenization imparted by disturbance of the arable layer. Accordingly, for the two top layers, the soils under no-tillage showed a lower H L I F than for conventionally tilled soils. Laser-induced fluorescence spectroscopy is a promising technique to assess humification in whole soil samples, particularly in Oxisols, which due to high concentration of Fe 3 + are not feasible to electron spin resonance (ESR) and Carbon-13 nuclear magnetic resonance ( 1 3 C NMR) spectroscopy, unless previous treatment is employed.

O objetivo do presente estudo foi avaliar o efeito do preparo do solo e formas de aplicação de calcário em experimento de longa duração, nas características de um Latossolo Bruno aluminíco argiloso e nos componentes do rendimento da cultura da soja. O experimento com sistemas de preparo do solo foi instalado em 1978, e, em 1987, métodos de aplicação de calcário foram introduzidos. Os tratamentos avaliados foram: PC sem - preparo convencional sem calcário; PC inc - com calcário; PD sem - plantio direto sem calcário; PD sup - com calcário superficial e PD inc - com calcário incorporado. O solo e a planta foram analisados na safra de 2002-2003. Os sistemas plantio direto e preparo convencional não apresentaram restrições físico-estruturais no solo. Na camada superficial, o plantio direto sem incorporação de calcário apresentou maior estabilidade dos agregados do que o preparo convencional. No PD inc, a estabilidade dos agregados foi menor do que no PD sem e PD sup. A estabilidade dos agregados mostrou-se positivamente relacionada com o comprimento de micélio fúngico e com o teor de CO. A umidade volumétrica e a água disponível na camada superficial foram maiores no PD sem e PD sup e de 0,20 a 0,30 m o PD sem armazenou mais água do que o preparo convencional. O sistema plantio direto apresentou mais CO e P do que o preparo convencional. O maior teor de P no solo favoreceu sua absorção e acúmulo no tecido da soja. A calagem reduziu o Al e elevou os teores de Ca, Mg e o pH do solo, e, no preparo convencional, aumentou o Mg, P e N no tecido, a altura de plantas e o peso de mil grãos, enquanto, no plantio direto, a calagem aumentou os teores de Ca e N no tecido, a altura de plantas e o peso de mil grãos. No plantio direto, a incorporação de calcário não afetou os nutrientes no tecido nem a produtividade da cultura, apenas aumentou a altura das plantas em relação ao PD sup. Portanto, no ambiente avaliado, não houve necessidade de incorporar calcário. A produtividade da soja não foi afetada pela calagem, mas foi 16 % maior no plantio direto em relação ao preparo convencional. The objective of this study was to evaluate the long-term effects of soil tillage systems and methods of lime application on biological, physical and chemical attributes of a clayey aluminic Oxisol, and on soybean yield components. The experiment with tillage systems was installed in 1978 in Guarapuava, PR, southern Brazil, and liming methods began to be tested in 1987. The treatments were: conventional tillage (CT) without liming; CT with liming; no-tillage (NT) without liming; NT with surface liming and NT with incorporated lime. Soil and plant analyses were performed during the 2002-2003 soybean growing season. No soil physical-structural restrictions were observed under CT and NT. In the surface soil layer NT with and without surface liming showed higher aggregate stability than CT. Aggregate stability was lower in NT with incorporated liming than in NT without soil mobilization. The aggregate stability was positively related to mycorrhiza mycelial length and organic carbon contents. The volumetric soil moisture and available water were higher in the surface layer in NT without and NT with surface liming. In the 0.20 to 0.30 m layer, NT without liming stored more water than CT. NT presented higher soil organic carbon and P contents than CT. The higher P content in the soil favours plant uptake and P accumulation in soybean leaf tissue. Liming reduced soil Al levels and increased soil pH and Ca and Mg contents. Liming under CT increased Mg, P and N contents in plant tissues, plant height and weight of 1,000 grains. Lime incorporation under NT did not affect tissue nutrient concentrations or soybean yield, but increased plant height in relation to NT with surface liming. Therefore, under the studied conditions it is not necessary to incorporate limestone under NT system. Soybean yield was not affected by liming, but it was 16% higher under NT than in CT.

Despite the low mobility in soil, surface liming has increased plant growth and yield. Since only the topsoil is affected by this technique, the benefits may be caused by improvements in soil solution. This experiment aimed to assess chemical changes in the solid phase and leached solutions after addition of calcitic limes to a Humic Hapludox. Calcium carbonate or calcium hydroxide was throughly mixed with soil samples at rates of 0, 0.25, 0.50, 1.0, and 1.50-times that required to raise soil pH to 6.0 (equivalent to 0, 3.5, 7.0, 14, and 21 t ha−1). After 60 days, treated samples were transferred to the top (30 cm) of leaching columns, filled with unlimed soil in the bottom (23 cm). Water was percolated weekly through the columns during 12 weeks. Chemical determinations were performed on all leached solutions, and at different soil depths below the limed layer at the end of the experiment. Calcium (Ca), magnesium (Mg), and aluminum (Al) increased linearly in the percolated solution with increases...

A viabilidade da aplicação de calcário sobre a superfície de solos em plantio direto e seu efeito na acidez em subsuperfície são pouco conhecidos. O presente estudo foi realizado em experimento de longa duração (21 anos), instalado, em 1978, em Guarapuava (PR), e teve por objetivo avaliar o efeito do método de reaplicação de calcário nos componentes da acidez das fases sólida e líquida de um Latossolo Bruno alumínico em plantio direto. Os tratamentos avaliados foram: sem calcário, calcário incorporado por uma lavração e duas gradagens e calcário aplicado sobre a superfície do solo, sem incorporação. Reaplicações de calcário foram realizadas em 1987 e 1995 nas doses de 4,5 e 3,0 Mg ha-1 de calcário, respectivamente. A amostragem de solo foi feita manualmente, em abril de 1999, em nove camadas até 0,4 m de profundidade. A reaplicação de calcário promoveu melhoria no ambiente químico do solo em plantio direto, evidenciada pela elevação do pH em água, dos teores de Ca e Mg trocáveis e em solução, da saturação por bases, bem como pela diminuição dos teores de Al trocável. A aplicação de calcário sobre a superfície do solo em plantio direto foi eficiente na elevação do pH na camada de 0-0,15 m e na elevação dos teores de Ca e Mg trocáveis e da saturação por bases, bem como na diminuição dos teores de Al trocável na camada de 0-0,20 m, não diferindo do tratamento com incorporação de calcário ao solo. A eficiência da calagem superficial na correção da acidez da camada arável do solo constitui importante indicativo da viabilidade desta prática em solos sob plantio direto de longa duração. The effect of surface liming on acidity components in the soil profile under long-term no-tillage system is largely unknown. This study was carried out in a long-term experiment (21 years) initiated in 1978 on a Brown Latosol (Haplohumox) located in Guarapuava County, Paraná State, South of Brazil. The aim was to evaluate the effect of lime reapplication methods on soil acidity attributes of both solid and liquid phases. Treatments consisted of: no liming, lime broadcast over the soil surface with no incorporation and lime applied on the soil surface followed by incorporation into the soil through plowing and double disking. Lime was reapplied twice, in 1987 and in 1995, at rates of 4.5 and 3.0 Mg ha-1, respectively. Soil samples were collected manually in April 1999, at nine soil layers up to a depth of 0.40 m. Lime reapplication improved the chemical environment of the soil under no-tillage, as evidenced by increases in water pH, exchangeable and soluble forms of Ca and Mg, base saturation in the cation exchange sites and by a decrease in exchangeable Al. The application of lime on soil surface followed by no incorporation was efficient in increasing soil pH up to a 0.15 m depth and increased exchangeable and soluble Ca and Mg and base saturation and reduced exchangeable Al in the 0-0.20 m layer. These effects were similar to those in the treatment with lime incorporation. The effectiveness of surface liming on soil acidity correction in the subsurface soil layer show that this practice is technically viable in soils under no-tillage for a long period.

Plantas de cobertura de inverno são fontes de C e de N em sistemas de produção de arroz irrigado, mas pouco se conhece sobre o efeito do manejo e da qualidade dos seus resíduos culturais nas emissões de metano (CH4) e de óxido nitroso (N2O) do solo. O estudo consistiu de um experimento conduzido em casa de vegetação e teve como objetivo principal avaliar a influência do manejo (incorporado ou em superfície) e do tipo de resíduos culturais (azevém e serradela) de plantas de cobertura sobre as emissões de CH4 e de N2O de um Planossolo Háplico sob cultivo de arroz irrigado por inundação. Utilizou-se o método da câmara fechada, e as concentrações de CH4 e de N2O nas amostras de ar foram determinadas por cromatografia gasosa. Coletas da solução do solo em duas profundidades (2 e 20 cm) foram realizadas simultaneamente às coletas de ar. A manutenção dos resíduos culturais na superfície do solo resultou em menor emissão de CH4 e de N2O em comparação à sua incorporação. O tipo de resíduo cultural não teve efeito na emissão de CH4, enquanto para o N2O a distinção entre os resíduos ocorreu apenas quando estes foram mantidos na superfície do solo – condição na qual as maiores emissões ocorreram com a adição dos resíduos da leguminosa (serradela). O processo mais intenso de redução do solo em subsuperfície (20 cm), evidenciado pelos maiores teores de íons reduzidos (Mn2+ e Fe2+), e a estreita relação entre a emissão de CH4 e os teores de C orgânico dissolvido nessa profundidade indicam que a camada subsuperficial foi a principal fonte de CH4 quando da incorporação dos resíduos culturais. A adoção de estratégias de manejo que promovam a manutenção dos resíduos culturais na superfície do solo é fundamental quando se visa à mitigação das emissões de CH4 e N2O em solos sob cultivo de arroz irrigado. O CH4 compõe mais de 90 % do potencial de aquecimento global parcial (CH4 + N2O) nesses sistemas de produção e, portanto, deve ser o foco principal da pesquisa. Winter cover crops are sources of C and N in flooded rice production systems, but very little is known about the effect of crop residue management and quality on soil methane (CH4) and nitrous oxide (N2O) emissions. This study was conducted in pots in a greenhouse to evaluate the influence of crop residue management (incorporated into the soil or left on the soil surface) and the type of cover-crop residues (ryegrass and serradella) on CH4 and N2O emissions from a flooded Albaqualf soil cultivated with rice (Oryza sativa L.). The closed chamber technique was used for air sampling and the CH4 and N2O concentrations were analyzed by gas chromatography. Soil solution was sampled at two soil depths (2 and 20 cm), simultaneously to air sampling, and the contents of dissolved organic C (DOC), NO3 -, NH4 +, Mn2+, and Fe2+ were analyzed. Methane and N2O emissions from the soil where crop residues had been left on the surface were lower than from soil with incorporated residues. The type of crop residue had no effect on the CH4 emissions, while higher N2O emissions were observed from serradella (leguminous) than from ryegrass, but only when the residues were left on the soil surface. The more intense soil reduction verified in the deeper soil layer (20 cm), as evidenced by higher contents of reduced metal species (Mn2+ and Fe2+), and the close relationship between CH4 emission and the DOC contents in the deeper layer indicated that the sub-surface layer was the main CH4 source of the flooded soil with incorporated crop residues. The adoption of management strategies in which crop residues are left on the soil surface is crucial to minimize soil CH4 and N2O emissions from irrigated rice fields. In these production systems, CH4 accounts for more than 90 % of the partial global warming potential (CH4+N2O) and, thus, should be the main focus of research.

O ambiente menos oxidativo do solo em plantio direto diminui o grau de humificação da matéria orgânica. Para testar esta hipótese, avaliou-se a concentração de radicais livres semiquinona (RLS) na matéria orgânica da camada superficial (0-25 mm) de um Cambissolo Húmico, cultivado por 8 anos nos sistemas preparo convencional (PC), preparo reduzido (PR) e plantio direto (PD), em Lages (SC). A concentração de RLS na matéria orgânica foi determinada por ressonância paramagnética eletrônica (EPR) nas frações granulométricas > 53, 53-20, 20-2 e < 2 µm. Na média das frações granulométricas, a concentração de RLS na matéria orgânica do solo foi menor em PD (15,83 x 10(17) spins g-1 C) do que em PC (18,33 x 10(17) spins g-1 C) e PR (18,39 x 10(17) spins g-1 C). A matéria orgânica na fração 20-2 µm apresentou a maior concentração de RLS e a menor largura de linha do sinal de EPR, o que é consistente com um maior grau de humificação e, ou, maior interação com a fração mineral, em comparação às frações > 53 e < 2 µm. Na fração 53-20 µm, os baixos teores de carbono orgânico não permitiram a detecção do sinal de EPR do RLS. Em adição ao efeito nos estoques de matéria orgânica, o PD resulta no decréscimo do grau de humificação, o que pode ter importante implicação na qualidade do solo. The less oxidative environment in soils of no-tillage systems decreases the humification degree of organic matter. To test this hypothesis, the concentration of semiquinone free radicals (SFR) of organic matter from the surface layer (0 to 25 mm) of a Humic Cambisol (Lages, Santa Catarina State) was evaluated. The soil had been cultivated for 8 yrs under conventional tillage (CT), reduced tillage (RT), and no-tillage (NT). The SFR concentration in organic matter was assessed by electron spin resonance (ESR) in the granulometric fractions (> 53, 53-20, 20-2, and < 2 µm). Among the tillage systems, the lowest concentration of SFR in the whole soil organic matter was observed in no-tilled soil (15.83 x 10(17) 'spins' g-1 C), in comparison with CT (18.33 x 10(17) 'spins' g-1 C) and RT (18.39 x 10(17) 'spins' g-1 C). Organic matter of the 20-2 µm size fraction showed a higher concentration of SFR and a smaller line width, which is consistent with a higher humification degree and/or higher interaction with soil minerals, in comparison with the size fractions > 53 and < 2 µm. The ESR signal of SFR was not detected in the 53-20 µm granulometric fraction due to the low organic C contents. In addition to the effect on soil C and N stocks, no-tillage decreases the humification degree of organic matter which may have an important influence on the soil quality.

The humification process increases semiquinone-type free radical concentrations (SFRC) in humus. Their quantification by electron spin resonance spectroscopy (ESR) has been a good indicator of the degree of humification of soil organic matter. As an alternative to relatively complex and expensive ESR spectroscopy, fluorescence spectroscopy was used in this study to evaluate the humification degree of 18 humic acids (HA) extracted from four Brazilian soils under different land use, tillage, or cropping systems. Two fluorescence humification indexes of HA were calculated based on work done by Zsolnay et al. and Kalbitz et al. in 1999, and a third new fluorescence index was proposed. Our proposal is to use the blue wavelength (465 nm) as the HA fluorescence excitation source. As this wavelength is more resonant with the humificated groups present in soil HA samples, our hypothesis is that the resultant fluorescence will provide information about these structures and, therefore, on the degree of humification of the HA. The SFRC varied from 1.90 × 10(17) to 14.75 × 10(17) spins/g HA, characterizing a wide range of the degree of humification of soil HA. The lowest SFRC occurred in native forests (1.90 × 10(17) to 7.50 × 10(17) spins/g HA) and pasture soils (2.30 × 10(17) to 4.64 × 10(17) spins/g HA). In cultivated sites, soil HAs from no-tillage soil were less humified (2.41 × 10(17) to 13.30 × 10(17) spins/g HA) than those in conventionally tilled soil (5.68 to 14.75 × 10(17) spins/g HA). The three fluorescence indexes show the same tendency as SFRC. Our fluorescence method was closely related to procedures found in the works of Zsolnay et al. and Kalbitz et al. (R∼0.9, P < 0.0001) and with SFRC (R∼0.85, P < 0.02), showing their potential as a simple and sensitive technique for evaluating the effect of land use and soil management systems on the humification degree of soil humic acids.

O uso de leguminosas para cobertura do solo e suprimento de N é uma técnica importante na conservação do solo e redução dos custos em fertilizantes minerais. No sul do Brasil, o enfoque principal da pesquisa tem sido sobre espécies de ciclo hibernal. No presente estudo, avaliou-se o efeito do cultivo intercalar de quatro leguminosas estivais [feijão-de-porco (Canavalia ensiformis ), guandu anão (Cajanus cajan), mucuna cinza (Stizolobium niveum ) e soja preta (Glycine sp.)] no fornecimento de N e rendimento de grãos do milho, em três doses de N mineral (0, 60 e 120 kg ha-1), em comparação a um tratamento-testemunha, sem leguminosa. Dois experimentos foram realizados, em sistema de preparo mínimo-PM (1993 a 1997), com abertura de sulcos para semeadura do milho feita com arado de tração animal, e em sistema de preparo convencional-PC (1994 a 1997), com aração e duas gradagens na primavera-verão, num Latossolo Vermelho distroférrico, em Chapecó (SC). Na média das safras, a produção de matéria seca das leguminosas estivais variou de 1,26 a 5,48 Mg ha-1, e o N na fitomassa da parte aérea, de 31 a 132 kg ha-1. Em comparação ao tratamento-testemunha, sem N mineral, as leguminosas aumentaram o rendimento do milho em 17 a 93 % (423 a 2.256 kg ha-1), no PC, e em 12 a 43 % (281 a 1.030 kg ha-1), no PM, sendo estes incrementos equivalentes à aplicação de 12 a > 120 kg ha-1 de N mineral no PC e de 50 a 86 kg ha-1 de N mineral no PM. Portanto, o cultivo intercalar de leguminosas estivais, além de proteger o solo, representa uma técnica promissora no forneci-mento de N e aumento de rendimento do milho, recomendada principalmente para pequenas propriedades rurais, onde a colheita do milho é manual. The use of legume cover crops contributes to soil conservation and would be an economical N source to maize. Since only winter legumes were evaluated in southern Brazil, this study was carried out to assess the effect of four intercropped summer species (Canavalia ensiformis, Cajanus cajan, Stizolobium niveum and Glycine sp.) on N supply and maize yield increase, in comparison with a control treatment, without legume cover crops. Cropping system effects on maize crop were evaluated under three mineral N rates (0, 60 and 120 kg ha-1), in two individual long-term trials, under reduced tillage (RT) or conventional tillage (CT), from 1993 to 1998. Both experiments were conducted on a Hapludox in the northwest of Santa Catarina State. Averaged across years, dry matter yield of legume species varied from 1.26 to 5.48 Mg ha-1, and N in aboveground phytomass from 31 to 132 kg ha-1. In comparison with the control treatment, without cover crops and mineral N, the legumes increased maize yield in a magnitude that ranged from 17 to 93 % (423 to 2256 kg ha-1) on CT, and from 12 to 43 % (281 to 1031 kg ha-1) on RT, and these increments were equivalent to those promoted by amounts of mineral N varying from 12 to > 120 kg ha-1 under CT, and from 50 to 86 kg ha-1, under RT. Besides protecting the soil, cultivation of summer legumes in a maize-legume intercrop enhances N availability and maize yield in the following season. Thus, it is an alternative N source, especially for small farms where maize is manually harvested.

Tillage system affects many soil parameters that may influence plant growth. This study evaluated the effect of liming on corn (Zea mays L.) yield and chemical characteristics of a Humic Hapludox (clayey, kaolinitic, goethitic, termic) under both conventional tillage (CT) and no-tillage (NT) systems. Rates of dolomitic lime, from 0 to 18 t ha -1 , were plowed into the soil in 1992 in southern Brazil; our study was conducted from 1996 through 1999. Lime rate was allocated to subplots, and tillage systems to main plots, in a split-plot design. Corn yield increased with liming in all years and was higher with CT than with NT in 2 of 3 yr. Averaged across years and systems, liming increased yield by 66%, which ranged from 4.4 to 7.8 t ha -1 . The highest average yield (7.8 t ha -1 ) was obtained at pH 6.5; yields at pH 6.0 or 5.5 were 97 and 89% of the maximum, respectively. Liming reduced soil organic matter (SOM) in both systems, but nutrients (P, K, Ca, Mg, Fe, Cu, Zn, and Mn) remained above sufficiency on all treatments. Aluminum, pH, SOM, and other nutritional parameters did not differ between tillage systems, partly because limestone was initially incorporated in all plots and partly due to dilution effects in the plow layer because sampling was not stratified in small depths. Some soil restriction impaired by absence of plowing, probably increases in bulk density, offset the benefits of NT on plant growth and was responsible for the smaller yield in this tillage system compared with CT.

O uso e manejo do solo podem afetar as frações lábeis e humificadas da matéria orgânica (MO), mas a magnitude destas alterações é pouco conhecida em ambientes subtropicais. Este estudo avaliou os efeitos de quatro sistemas de uso e manejo do solo (mata, campo nativo, preparo convencional e plantio direto na sucessão trigo/soja) sobre (i) o estoque de carbono orgânico total (COT) (0-250mm), e nos (ii) estoques de carbono (C) em frações lábeis (grosseira, leve) e humificadas (associada aos minerais, substâncias húmicas) da MO na camada superficial (0-25mm) de um Latossolo bruno, no Sul do Brasil. Comparado à mata, o solo sob preparo convencional apresentou 36% (46,2Mg ha-1) menos COT na camada de 0-250mm, bem como um decréscimo generalizado no estoque de C em todas frações da MO na camada de 0-25mm. As frações grosseira (>53 m) e leve (53 mm) and light (

Assessment of particulate (>53-μm) and mineral-associated (

Long-term (5- and 9-year) effects were evaluated of two tillage regimes (conventional tillage: CT; and no-tillage: NT) and two cropping systems (oat/maize: O/M; and oat+vetch/maize+cowpea: O+V/M+C) on characteristics of humic acids (HAs) from surface layer (0 to 25 mm) of a subtropical Brazilian Paleudult soil. Generally, soil HA samples from conservation management systems with no soil disturbance (NT) and high crop residue addition (O+V/M+C) showed lowest humification degree, as demonstrated by lowest concentration of semiquinone-type free radicals, determined by electron spin resonance (ESR), and lowest total fluorescence (TF), which is proportional to area under fluorescence spectrum; however, cropping systems had less effect than tillage regimes on two spectroscopic parameters. Since all HA samples presented a maximum fluorescence emission peak around 518 nm, when excited with blue light, we believe that differences in the fluorescence intensity could be attributed to concentration of similar condensed aromatic moiety. This assumption was consistent with strong correlation with stable semiquinone-type free radicals (r=0.84, P

Soil carbon accumulation is largely dependent on net primary productivity. To our knowledge, there have been no studies investigating the dynamics of carbon accumulation in weathered subtropical soils, especially in managed eucalyptus plantations. We quantified the seasonal input of leaf litter, the leaf decomposition rate and soil carbon stocks in an commercial plantation of Eucalyptus saligna Labill. in southern Brazil. Our goal was to evaluate, through multiple linear regression, the influence that certain chemical characteristics of litter, as well as chemical and physical characteristics of soil, have on carbon accumulation in soil organic matter fractions. Variables related to the chemical composition of litter were not associated with the soil carbon stock in the particulate and mineral fractions. However, certain soil characteristics were significantly associated with the carbon stock in both fractions. The concentrations of nutrients associated with plant growth and productivity, such as phosphorus, sulfur, copper and zinc, were associated with variations in the labile carbon pool (particulate fraction). Clay content was strongly associated with the carbon stock in the mineral fraction. The carbon accumulation and stabilization in weathered subtropical Ultisol seems to be mainly associated with the intrinsic characteristics of the soil, particularly clay content, rather than with the quantity, chemical composition or decomposition rate of the litter.

Soil can be either source or sink of methane (CH4), depending on the balance between methanogenesis and methanotrophy, which are determined by pedological, climatic and management factors. The objective of this study was to assess the impact of drainage of a highland Haplic Histosol on CH4 fluxes. Field research was carried out in Ponta Grossa (Paraná, Brazil) based on the measurement of CH4 fluxes by the static chamber method in natural and drained Histosol, over one year (17 sampling events). The natural Histosol showed net CH4 eflux, with rates varying from 238 µg m-2 h-1 CH4, in cool/cold periods, to 2,850 µg m-2 h-1 CH4, in warm/hot periods, resulting a cumulative emission of 116 kg ha-1 yr-1 CH4. In the opposite, the drained Histosol showed net influx of CH4 (-39 to -146 µg m-2 h-1), which resulted in a net consumption of 9 kg ha-1 yr-1 CH4. The main driving factors of CH4 consumption in the drained soil were the lowering of the water-table (on average -57 cm, vs -7 cm in natural soil) and the lower water content in the 0-10 cm layer (average of 5.5 kg kg-1, vs 9.9 kg kg-1 in natural soil). Although waterlogged Histosols of highland areas are regarded as CH4 sources, they fulfill fundamental functions in the ecosystem, such as the accumulation of organic carbon (581 Mg ha-1 C to a depth of 1 m) and water (8.6 million L ha-1 = 860 mm to a depth of 1 m). For this reason, these soils must not be drained as an alternative to mitigate CH4 emission, but effectively preserved. O solo pode atuar como fonte ou sumidouro de metano (CH4), dependendo do balanço entre metanogênese e metanotrofia, definido por fatores pedológicos, climáticos e de manejo. O objetivo deste estudo foi avaliar as implicações da drenagem do Organossolo Háplico hêmico, típico em campo hidrófilo de altitude sobre os fluxos de CH4. A pesquisa de campo foi conduzida no município de Ponta Grossa, PR, e envolveu avaliações de fluxos de CH4 pelo método da câmara estática em Organossolo natural e Organossolo drenado, por um período de um ano (17 coletas). No Organossolo natural, ocorreu efluxo líquido de CH4, com taxas variando entre 238 µg m-2 h-1 de CH4, em épocas mais frias, e 2.850 µg m-2 h-1 de CH4, em épocas mais quentes, totalizando emissão acumulada de 116 kg ha-1 ano-1 de CH4. Na área drenada, ocorreu influxo líquido (-39 a -146 µg m-2 h-1 de CH4), que totalizou em consumo de 9 kg ha-1 ano-1 de CH4. O rebaixamento do nível freático (em média -57 cm, contra -7 cm no solo natural) e a menor umidade gravimétrica na camada de 0-10 cm (média de 5,5 kg kg-1, contra 9,9 kg kg-1 do solo natural) foram os principais fatores determinantes do consumo de CH4, na área drenada. Apesar de os Organossolos em campo hidrófilo atuarem como fonte de CH4, esses possuem importantes funções no ecossistema, como acumular carbono orgânico (581 Mg ha-1 de C até 1 m) e armazenar água (8,6 milhões de L = 860 mm até 1 m). Por essa razão, não devem ser drenados, como alternativa para redução da emissão de metano, mas efetivamente preservados.

Among the various sources with a potential negative impact on the environment, methane (CH4) emissions from livestock origin have been highlighted as important for the agricultural sector. Research to mitigate CH4 emissions and understand how integrated crop and livestock production systems may contribute to the reduction of greenhouse gases, is essential for the development of public policies for environmental preservation. We hypothesized that combinations of stocking methods and grazing intensities provokes differences in the quantity and quality of herbage ingested, thus altering animal production and CH4 emissions by the grazing animal. Experiments were carried out in 2011 (Experiment 1) and 2012 (Experiment 2), when the production of pasture and CH4 emissions from sheep were studied in a system that integrates soybean (Glycine max. (L.) Merr.) and maize (Zea mays L.) in the summer/autumn, in rotation with Italian ryegrass (Lolium multiflorum Lam.) in winter/spring. Two stocking methods (continuous or rotational) and two grazing intensities (herbage allowance: moderate and low, 2.5 and 5 times the potential daily dry matter intake, respectively) in a randomized complete block design with three replicates were studied. Lambs were used in the first experiment, while lactating ewes (all with a single lamb) were used in the second experiment. Average daily gain (ADG) of lambs was greater (P < 0.05) in continuous than in rotational stocking, regardless of grazing intensity (150 vs. 89 g day−1 and 241 vs. 209 g day−1 in Experiments 1 and 2, respectively). Ewe ADG did not differ (P > 0.05) between treatments. Live weight gain per hectare (LWGHA) showed the same response in both experiments, with greater LWGHA in moderate grazing intensity (P < 0.05). In Experiment 1, the dry matter intake (DMI) was on average 21% greater (P < 0.05) for continuous stocking than rotational stocking (1345 g day−1 vs. 1075 g day−1, respectively), while in Experiment 2, no differences (P > 0.05) between stocking methods and grazing intensities were observed (1673 ± 83 g day−1). The CH4 emissions per animal did not differ (P > 0.05) among treatments in both experiments (22.7 ± 1.0 and 39.9 ± 1.3 g day−1, Experiments 1 and 2, respectively), but when expressed in g CH4 kg ADG−1 emissions were on average 35 and 15% greater (Experiments 1 and 2, respectively) (P < 0.05) under rotational than continuous stocking, independent of grazing intensity (171 vs. 263 g CH4 kg ADG−1 and 171 vs. 202 g CH4 kg ADG−1 in Experiments 1 and 2, respectively). Stocking method was more important than grazing intensity in determining methane production by grazing sheep. Continuous stocking was the most efficient grazing management in reducing methane emissions per unit animal production. Fil: Savian, Jean Victor. Universidade Federal do Rio Grande do Sul; Brasil Fil: Barth Neto, Armindo. Universidade Federal do Rio Grande do Sul; Brasil. Universidade Federal do Paraná; Brasil Fil: Bitencourt de David, Diego. Universidade Federal do Rio Grande do Sul; Brasil. Fundação Estadual de Pesquisa Agropecuária; Brasil Fil: Bremm, Carolina. Universidade Federal do Rio Grande do Sul; Brasil. Fundação Estadual de Pesquisa Agropecuária; Brasil Fil: Marinho Três Schons, Radael. Universidade Federal do Rio Grande do Sul; Brasil Fil: Moraes Genro, Teresa Cristina. Ministerio da Agricultura Pecuaria e Abastecimento de Brasil. Empresa Brasileira de Pesquisa Agropecuaria; Brasil Fil: Amaral, Glaucia Azevedo do. Fundação Estadual de Pesquisa Agropecuária; Brasil. Universidade Federal do Rio Grande do Sul; Brasil Fil: Gere, José Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: McMagnus, Concepta Margaret. Universidade Federal do Rio Grande do Sul; Brasil Fil: Bayer, Cimélio. Universidade Federal do Rio Grande do Sul; Brasil Fil: Faccio Carvalho, Paulo César de. Universidade Federal do Rio Grande do Sul; Brasil

7 páginas.-- 4 tablas.-- 40 referencias, Integrated crop-livestock (ICL) is a promising land use system for the Brazilian Cerrado, but little is known about what this system might change in chemical composition of soil organic matter. In three long-term experiments (9–11 years old), located on Cerrado Ferralsols in Dourados, Maracaju and Campo Grande (Mato Grosso do Sul State, Brazil), we assessed the impact of continuous cropland (CC), ICL, and permanent pasture of Brachiaria decumbens (PP) on the C concentration and composition of the free light fraction (FLF), occluded light fraction (OLF) and heavy fraction (HF) of soil in the 0–5 cm layer. CPMAS13C NMR spectroscopy was used to determine the percentage of alkyl, O-alkyl, aromatic and carboxyl C types. In Dourados and Maracaju, PP had the highest concentrations of organic C in whole soil and physical fractions, while ICL was intermediate and CC lowest. In Campo Grande, soil organic C concentration was similar among management systems. Distribution of organic C across physical fractions was not affected by management nor by experimental site, and on average the FLF, OLF and HF contained 7%, 26% and 67% of the total storage, respectively. Signal peaks of the four main C types appeared in all CPMAS 13C NMR spectra, but at different intensities. O-alkyl was the major C type (about 50%), carboxyl was the minor representative (generally less than 10%) and alkyl and aromatic C were intermediates. From FLF to OLF, the alkyl and aromatic C concentrations increased, possibly due to selective preservation of waxes, resins, cutin, suberin and lignin. The HF had greater O-alkyl and lower aromatic C concentrations than OLF, which might have been related to the accumulation of microbial carbohydrates on mineral surfaces of the HF. Along the sequence CC–ICL–PP, the most evident changes were greater of O-alkyl and lower alkyl C types, practically in all fractions and sites. In FLF and OLF, these changes were attributed to greater biomass input and less seed drill-induced disturbance of soil surface (lower decomposition of residues) in the PP and ICL. Additionally, in OLF, greater O-alkyl concentration in PP and ICL was attributed to physical protection of particulate organic matter derived from grass roots occluded inside soil aggregates. Our results suggest that PP and ICL systems increased or maintained soil organic C concentrations compared to CC, associated with a qualitative increase of the chemically labile O-alkyl C type which was possibly related to greater biomass addition and less soil disturbance.

The low phosphorus availability in tropical and subtropical soils, normally related to adsorption of phosphate to the minerals surfaces, can be attenuated when organic matter (OM) accumulates in the soils. Herein, we report the results of long-term experiments (18-32 years) aimed at quantifying the maximum phosphorus adsorption capacity (MPAC) and its determinant mineralogical variables in Brazilian soils and at assessing the effect of no-tillage (NT) in mitigating the phosphorus adsorption of soils. The MPAC of soils ranged from 297 to 4,561 mg kg-1 in the 0.00-0.10 m layer and from 285 to 4,961 mg kg-1 in the 0.10-0.20 m layer. The MPAC was correlated with the concentrations of iron oxides, goethite and ferrihydrite, gibbsite/(gibbsite+kaolinite) ratio and the specific surface area. The OM increased in the 0.00-0.10 m layer of NT soils, which was not reflected on the decrease of MPAC for the no-tillage soils. A baixa disponibilidade de fósforo em solos tropicais e subtropicais, normalmente relacionada à adsorção de fosfato pelas superfícies minerais, pode ser atenuada quando matéria orgânica (MO) é acumulada nos solos. Em experimentos de longa duração (18-32 anos) em solos brasileiros, o estudo objetivou quantificar a capacidade máxima de adsorção de fósforo (CMAP) e as variáveis mineralógicas determinantes, bem como verificar o efeito do plantio direto em mitigar a adsorção de fósforo nos solos. A CMAP dos solos variou de 297 a 4.561 mg kg-1 na camada 0,00-0,10 m e de 285 a 4.961 mg kg-1 na camada 0,10-0,20 m. A CMAP apresentou relação com a concentração de óxidos de ferro, de goethita e de ferrihydrita, com a razão gibbsita/(gibbsita+caulinita) e com a área superficial específica do solo. O conteúdo de MO aumentou na camada 0,00-0,10 m dos solos em plantio direto e não afetou a CMAP em comparação aos solos em sistema de preparo convencional.

Os benefícios do calcário aplicado sobre a superfície do solo no rendimento vegetal podem estar associados à melhoria na composição química das águas de percolação. Esse trabalho objetivou avaliar alterações na fase sólida e na solução percolada em dois solos ácidos (Latossolo Bruno Álico e Cambissolo Húmico Álico), ocasionadas pelo método de aplicação (na superfície ou incorporado) de corretivos da acidez (CaCO3 e MgCO3) e de gesso agrícola. O CaCO3 foi utilizado na dose equivalente a 0,25 daquela necessária para elevar o pH a 6,0, e os demais em doses molares equivalentes. O CaCO3 foi ainda incorporado nas doses de 0; 0,5; 1,0 e 1,5 vez a necessidade de calcário para pH 6,0. Em colunas de lixiviação, com 1,5 kg de solo, percolou-se água destilada durante 12 semanas num volume de 200 mL semana-1. Os corretivos da acidez, quando incorporados aos solos, aumentaram o pH das duas fases, diminuíram o Al trocável, porém não afetaram o Al percolado; quando foram aplicados na superfície, não afetaram nenhum parâmetro da solução percolada, e alteraram a composição química somente da camada de 0 a 2,0 cm de profundidade. O gesso agrícola diminuiu o pH do solo e da solução percolada, não afetou o Al trocável, mas percolou muito mais Ca, Mg e Al que os corretivos da acidez, principalmente quando foi incorporado ao solo. A mobilidade dos cátions integrantes dos corretivos foi muito pequena, e a aplicação de calcário na superficie dos solos não afetou a composição química da solução coletada 30 cm abaixo. The increase on crop yield caused by lime addition on the soil surface may be associated to improvements in the chemical composition of the percolating water. This study was carried out to evaluate chemical changes in the solid phase and in the percolating water in two acid soils (Oxisol and Inceptisol) caused by the application method (incorporated or on soil surface) of gypsum, CaCO3, or MgCO3. Calcium carbonate was used at a rate equivalent to 0.25 of that recommended by the SMP method to raise soil water pH to 6.0; gypsum and MgCO3 were used at the same molarity rate. Additional CaCO3 were (0, 0.50, 1.0 and 1.5 times that recommended by the SMP method) was also incorporated. Treated soil samples (1.5 kg) were transferred to leaching columns, and distilled water (200 mL column-1 week-1) were added on soil surface during twelve weeks. Incorporation of lime (CaCO3 and MgCO3) into the soils increased pH of both phases, decreased exchangeable Al, but had no effect on Al in the percolated solution. When carbonates were applied on soil surface, they had no effect on the leached solution, and affected the chemical composition of the solid phase only in the top 2.0 centimeters. Addition of gypsum decreased soil and solution pH, had no effect on exchangeable Al, but leached greater amounts of Ca, Mg and Al than limestone, especially when gypsum was incorporated. Cation mobility from limestone materials was negligible, and surface liming had no chemical effects in the solution collected 30 cm below soil surface.

Apesar da baixa mobilidade do P no solo, os fertilizantes fosfatados estão sendo aplicados sobre a superfície, em alguns sistemas de cultivo. Pouco se conhece sobre a eficiência dessa forma de aplicação, a qual pode ser influenciada pela característica dos fosfatos e pelo pH do solo. Este trabalho objetivou avaliar o efeito do método de aplicação (superficial ou incorporado) de alguns fertilizantes fosfatados (diamônio fosfato - DAP, superfosfato triplo e fosfato natural ARAD), em dois valores de pH (com e sem calcário), em algumas características químicas do solo e no rendimento de massa seca de milho. Cultivou-se milho durante 21 dias, em câmara de crescimento, em unidades experimentais com 3,0 kg de solo (base seca). Na ausência de calcário (pH 4,7), a aplicação dos fosfatos na superfície do solo proporcionou maiores rendimentos de massa seca e maior absorção de P pelo milho do que a incorporação dos fosfatos, sendo o DAP o fertilizante mais eficiente. Na presença de calcário (pH 5,7), não houve diferença entre os métodos de aplicação, e os maiores rendimentos foram obtidos com as fontes solúveis. A aplicação dos fosfatos na superfície do solo aumentou a concentração de P até 3 cm de profundidade. Na ausência de déficit hídrico, o milho foi eficiente em absorver o P aplicado sobre a superfície do solo a partir de fontes solúveis em água, mesmo tendo havido baixa mobilidade vertical do nutriente. Phosphorus has very low mobility into the soil, but in spite of this, it has been applied on the soil surface on some soil tillage systems. The efficiency of this form of application is not well known yet but can be affected by the soil pH and type of phosphate applied. This study aimed to assess the effect of the application method (mixed into the soil or on the surface, without incorporation) of phosphate fertilizers (diammonium phosphate, triple superphosphate, and ARAD rock phosphate), at two pH values (with and without lime), on some soil chemical characteristics and on corn dry matter yield. Corn plants were grown during 21 days after seed emergence in a growth chamber, in experimental units of 3.0 kg of soil (dry basis). In absence of liming (pH-H2O 4.7), addition of phosphates on the soil surface gave better yield and higher P uptake than their incorporation into the soil, and diammonium phosphate was the most efficient source. On limed soil (pH-H2O 5.7), there was no difference between the application methods, and the best yields were obtained with the soluble phosphate sources. Addition of phosphate fertilizers on the soil surface increased P in the soil up to 3 cm depth. In absence of water deficit, corn plants could obtain enough P from soluble phosphates added to the soil surface, despite their low mobility.

O uso de leguminosas constitui boa alternativa para suprir N e aumentar o rendimento das culturas comerciais. A aceitação desta prática por agricultores e extensionistas, entretanto, depende da demonstração de sua vantagem econômica em relação ao sistema tradicional. Neste estudo, avaliou-se o efeito do cultivo intercalar de quatro leguminosas estivais de cobertura do solo [feijão de porco (Canavalia ensiformis L.), guandu (Cajanus cajan L.) cv. roxo anão, mucuna cinza (Stizolobium niveum Kuntze) e soja preta (Glycine sp)] sobre a receita líquida da cultura do milho, em três doses de N (0, 60 e 120 kg ha-1), comparativamente ao sistema tradicional de milho exclusivamente (testemunha). Dois experimentos foram realizados, durante quatro e cinco anos, respectivamente, em sistemas de preparo convencional (PC) e preparo reduzido (PR), num Latossolo Vermelho distroférrico, em Chapecó (SC), sendo os resultados apresentados na média das safras. A cultura do milho, sem leguminosa e sem adubação nitrogenada, apresentou uma receita líquida de 45 R$ ha-1 no PC e de 72 R$ ha-1 no PR. O cultivo intercalar das leguminosas promoveu incrementos na receita líquida da cultura do milho que variaram de 64 a 312 R$ ha-1 (142 a 693%), no PC, e de 57 a 147 R$ ha-1 (79 a 204%), no PR, na ausência de adubação nitrogenada. Mesmo com aplicação de N, as leguminosas promoveram aumento na receita líquida da cultura do milho, porém de menor magnitude. O cultivo intercalar de leguminosas estivais de cobertura do solo demonstrou-se uma alternativa viável para aumentar a receita líquida da cultura do milho. Os benefícios econômicos obtidos com esta prática provavelmente compensam o aumento em mão-de-obra. Legumes cover-crops represent a good alternative to supply N as well as to improve yield of commercial crops. The acceptance of this technique by growers and extension agents, however, depends on its economical advantage in relation to traditional systems. In this study, the effect of four summer legumes cover-crops (Canavalia ensiformis, Cajanus cajan, Stizolobium niveum and Glycine sp), was evaluated in association with three N rates (0, 60 and 120 kg ha-1), on the net income of corn. Two medium-term (4- and 5-yr) experiments were carried out, respectively, under conventional tillage (CT) and reduced tillage (RT), in the Northwest of Santa Catarina State, Brazil. In absence of cover-crops and mineral N, corn production gave a net income of 25 and 40 U$ ha-1 (1 U$ = 1.80 R$), respectively, on CT and on RT. The use of cover-crops raised the net income from 35 to 173 U$ ha-1 (142 a 693%) under CT, and from 32 to 82 U$ ha-1 (79 a 204%) under RT, in absence of N. When N was applied, the economic benefits of such crops were smaller, but still advantageous. Thus, cultivation of summer legumes in the inter-rows of corn, as cover-crops, has economical advantages, probably enough to off-set the higher costs of family labor involved.

Conservation management systems increase soil C and N pools. However, their effects on particulate (>53 μm) and mineral-associated (

A interação de substâncias húmicas com minerais no solo pode influir na dinâmica da decomposição da matéria orgânica e na sua estabilidade. A adsorção de dois ácidos húmicos em Latossolo Roxo natural (LR natural) e tratado com oxalato de amônio (LR tratado) foi efetuada, com vistas em investigar os mecanismos de adsorção e os principais grupos funcionais envolvidos, bem como relacionar a capacidade adsortiva de acordo com as características químicas e moleculares dos adsorbatos. Os ácidos húmicos extraídos com solução de NaOH 0,5 N de uma amostra de carvão (AHc) e de um solo Brunizém (AHs) foram caracterizados por análise elementar e espectroscopia de 13C-RMN. A parametrização dos dados experimentais das isotermas de adsorção foi do tipo y = A tanh Bx, e o modelo de Langmuir também foi aplicado. As amostras adsorvidas foram analisadas por espectroscopia no Infra-Vermelho por Reflectância Difusa com Transformada de Fourier (DRIFT). A adsorção dos ácidos húmicos no LR natural foi de natureza química, sendo evidenciado por DRIFT que a reação de troca de ligantes das carboxilas com a superfície dos minerais foi um mecanismo importante. O AHc, que apresentou caráter aromático mais elevado e maior teor de carboxilas na molécula, foi adsorvido em maior quantidade do que o AHs nos dois adsorventes, o que indica a possível participação de estruturas aromáticas na interação organomineral No LR tratado, cuja área superficial específica foi superior (ASE = 140,9 m2 g-1), a adsorção foi mais elevada do que no LR natural (ASE = 66,1 m2 g-1). A maior ASE no LR tratado foi relacionada com o rompimento de microagregados no tratamento com oxalato de amônio que extraiu a porção cimentante dos óxidos de ferro que unia os minerais. A interação neste tipo de adsorvente, estimada segundo a equação y = A tanh Bx, foi mais forte do que na amostra natural, o que pode estar relacionado com a presença de sítios de adsorção hidrofóbica pela presença do oxalato na superfície, com a exposição de sítios mais reativos após tratamento e pH mais ácido. O modelo de Langmuir mostrou-se adequado para explicar a adsorção na amostra natural, enquanto, no LR tratado com oxalato de amônio, o ajuste não foi satisfatório. Em geral, a aplicação da equação y = A tanh Bx forneceu melhor ajuste (R2 maior) do que a equação de Langmuir. The adsorption of two humic acids (HA) was carried out on a natural Oxisol (natural LR) and on an ammonium-oxalate treated sample (treated LR), in order to investigate the adsorption mechanisms and the main functional groups involved and relate the adsorptive capacity with the chemical and molecular characteristics of the adsorbates. The HA extracted with 0.5 N NaOH solution from a coal sample (HAc) and from a Mollisol sample (HAs) were characterized by elemental analysis and 13C-NMR spectroscopy. The experimental data were fitted according to the equation y = A tanh Bx and the model of Langmuir was also applied. The adsorbed samples were analyzed by Diffuse Reflectance Fourier Transformed Infrared Spectroscopy (DRIFT). The HA adsorption on the natural LR was of a chemical nature, with the ligand exchange reaction between the carboxyl groups and the mineral surfaces being an important mechanism, as shown by DRIFT. The AHc had a higher aromatic character and a higher carboxyl content in its molecule and was adsorbed in greater quantity than the AHs in both adsorbents. This result also suggests a possible participation of aromatic moieties in the organo-mineral interaction The treated LR, which had a higher specific surface area (SSA = 140.9 m2 g-1), showed a greater adsorptive capacity than the natural LR (SSA = 66.1 m2 g-1). The higher SSA in the treated sample was related to the breakup of microaggregates by the oxalate treatment, caused by the extraction of the cementing portion of iron oxides that bonded the particles together. The interaction in this adsorbent, as estimated by the parametrization y = A tanh Bx, showed higher chemical affinity than in the natural sample. This can be related to the adsorbed oxalate that created hydrophobic adsorption sites, the exposure of more reactive sites after the treatment and the lower pH value. The Langmuir model was adequate to explain the adsorption in the natural sample, while in the treated sample, the results obtained were not satisfactory. Generally, the proposed parametrization y = A tanh Bx yielded the better fit (i.e. higher R2) in comparison to the Langmuir equation.

A calagem altera algumas propriedades eletroquímicas em solos de carga variável e isso pode afetar a dispersão da argila e a estabilidade dos agregados. Essa hipótese foi avaliada por meio da aplicação de quantidades crescentes de calcário (0, 4,5, 9,0, 13,5 e 18,0 t ha-1) num Latossolo Bruno (Haplohumox). O calcário foi aplicado em parcelas de campo e incorporado até 17 cm de profundidade, na primavera de 1992, e as amostras para as determinações deste estudo foram coletadas na primavera de 1997. Durante esse período, o solo foi cultivado com milho no verão e permaneceu em pousio no inverno. A calagem aumentou o ponto de efeito salino nulo, PESN (R² = 0,85*), o potencial elétrico negativo superficial (R² = 1,00**) e a argila dispersa em água (R² = 0,93**), diminuiu os teores de matéria orgânica (R² = 0,83*) e não afetou o diâmetro médio ponderado dos agregados. O aumento do PESN ocorreu, provavelmente, pela diminuição dos teores de matéria orgânica. A argila dispersa em água foi positivamente correlacionada com o potencial elétrico superficial (R² = 0,93**) e o seu aumento deveu-se, provavelmente, a maior repulsão entre as partículas do solo em conseqüência do incremento das cargas negativas e da espessura da dupla camada elétrica difusa. Liming influences some electrochemical properties of soils of variable charge that may affect clay dispersion and aggregate stability. This hypothesis was tested after five years of incorporation of increasing rates of limestone (0, 4.5, 9.0, 13.5 and 18 t ha-1) into a Brown Latosol (Haplohumox). Dolimitic limestone was plowed down to 17 cm depth into the soil during the spring of 1992 when field plots began to be cultivated annually with continuous corn. Soil samples used in this work were collected in the spring of 1997. Liming increased the amount of clay dispersed in water (R² = 0.93**), negative surface electric potential (R² = 1.00**), point of zero salt effect PZSE (R² = 0.85*) and slightly decreased soil organic matter (R² = 0.83*), but had no effect on soil aggregate stability. The increase on PZSE was probably caused by the decrease of soil organic matter. Clay dispersion was positively associated with surface electric potential (R² = 0.93**) and its increase was probably due to higher repulsive forces among soil particles as a consequence of either increases on CEC and on thickness of electric double layer.

Soil organic matter decline and associated degradation of soil and environmental conditions under conventional tillage in tropical and subtropical regions underline the need to develop sustainable soil management systems. This study aimed first to evaluate the long-term effect (9 years) of two soil-tillage systems (conventional tillage: CT, and no-tillage: NT) and two cropping systems (oat (Avena strigosa Schreb)/maize (Zea mays L.): O/M; and oatacommon vetch (Vicia sativa L.)/ maizeacowpea (Vigna unguiculata (L.) Walp): OaV/MaC without N fertilization on total organic carbon (TOC) and total nitrogen (TN) concentrations in a sandy clay loam Acrisol in southern Brazil. The second objective was to assess soil potential for acting as an atmospheric CO2 sink. Under NT an increase of soil TOC and TN concentrations occurred, in both cropping systems, when compared with CT. However, this increase was restricted to soil surface layers and it was higher for OaV/MaC than for O/M. The OaV/MaC under NT, which probably results in the lowest soil organic matter losses (due to erosion and oxidation) and highest addition of crop residues, had 12 Mg ha ˇ1 more TOC and 0.9 Mg ha ˇ1 more TN in the 0‐30.0 cm depth soil layer, compared with O/M under CT which exhibits highest soil organic matter losses and lowest crop residue additions to the soil. These increments represent TOC and TN accumulation rates of 1.33 and 0.10 Mg ha ˇ1 per year, respectively. Compared with CT and O/M, this TOC increase under NT and OaV/MaC means a net carbon dioxide removal of about 44 Mg ha ˇ1 from the atmosphere in 9 years. NT can therefore be considered, as it is in temperate climates, an important management strategy for increasing soil organic matter. In the tropicals and subtropicals, where climatic conditions cause intense biological activity, in order to maintain or increase soil organic matter, improve soil quality and contribute to mitigation of CO2 emissions, NT should be associated with cropping systems resulting in high annual crop residue additions to soil surface. # 2000 Elsevier Science B.V. All rights reserved.

In weathered tropical and subtropical soils organic matter is crucial for soil productivity and its quantity depends heavily on soil management systems. This study evaluated the effect of no-till cropping systems on organic matter content and quality in a sandy clay loam Acrisol soil (Paleudult in US taxonomy) from Southern Brazil. Ten cropping systems with varying additions of C and N were conducted for 12 years (from 1983 to 1994). The addition of crop residues increased total organic carbon (TOC) and total nitrogen (TN) in the soil at 0‐17.5 cm depth, and this increase was directly related with C and N added or recycled by the systems. The crop residues added to the soil were associated with reduced semiquinone free radical concentration, detected by electron spin resonance (ESR), in the organo-mineral aggregates

A associação de preparos conservacionistas com culturas de cobertura é importante estratégia de melhoria da qualidade do solo. Quando leguminosas são utilizadas, verifica-se incremento na disponibilidade de nitrogênio (N) para a primeira cultura em sucessão (efeito imediato). Todavia, o uso de leguminosas por vários anos pode se refletir no incremento da capacidade do solo em suprir N (efeito residual). Com o objetivo de distinguir o efeito residual do efeito imediato do uso de culturas de cobertura foi realizada esta pesquisa. Utilizou-se um experimento de longa duração (1985 a 1995) instalado na Estação Experimental Agronômica da UFRGS, RS. O delineamento experimental foi o de blocos casualizados com parcelas subsubdivididas e três repetições. As parcelas principais incluíram três sistemas de preparo: convencional, reduzido e direto; as subparcelas abrangeram três sistemas de cultura: aveia/milho (A/M), aveia + ervilhaca/milho (A + E/M) e aveia + ervilhaca/milho+caupi (A + E/M + C) e as subsubparcelas doses de N. O solo da área experimental é um Podzólico Vermelho-Escuro. No ano desta pesquisa (1995), os sistemas de cultura utilizados foram aveia/milho, ervilhaca/milho e aveia + ervilhaca/milho. Visando avaliar o efeito residual do uso de culturas de cobertura, um segmento da parcela foi mantido descoberto durante o inverno que antecedeu o cultivo do milho. A associação de preparos conservacionistas (reduzido e direto) com o uso de leguminosas aumentou o estoque de N total na camada superficial do solo. O efeito residual das leguminosas no sistema A + E/M + C promoveu incrementos de 26 e 19% na quantidade de N absorvido e rendimento de grãos, respectivamente, em relação ao histórico de uso de A/M. Contudo, a presença de resíduos de ervilhaca ainda foi a principal responsável pelo fornecimento de N ao milho (efeito imediato). The association of conservation tillage with cover crops is an important tool for improving soil quality. When legumes are used as cover crops there is an increase in nitrogen (N) availability for the first crop in succession (immediate effect). However, the long term use of legumes as cover crop increases soil N availability (residual effect). This long-term experiment was carried out to evaluate the immediate effect and residual effect of cover crops on a Paleadulf from Rio Grande do Sul, Brazil. The experimental design was a split split plot with three replications. The main plots were three tillage systems: conventional, minimum and no-tillage; the subplot consisted of three crop productions: black oat/corn (A/M), oat + common vetch/corn (A + E/M), oat + common vetch/corn + cowpea (A + E/ M + C), and the subsubplots consisted of two N fertilizer rates: 0 and 120 kg ha-1. The crop production systems used were: oat/corn, vetch/corn and oat + vetch/corn. In order to evaluate the residual effect of cover crop, the plots were split in bare soil before corn cropping and cover with cover crop. Conservation tillage plus legume cover crop increased total N at soil surface. The use of legumes in A + E/M + C, regardless of the tillage system, increased corn N uptake by 26% and increased corn yield by 19%, when compared to A/M. Despite that, cover crop biomass in the presence of corn was considered the most important N source to corn.

This study evaluated the chemical composition and distribution patterns of soil organic matter (SOM) of Oxisol under native pasture without burning for the last 41 years (NP), native pasture without burning for the last eight years (BP), native pasture in soil amended by liming and fertilization and without burning for the last 41 years (AP), and native forest (NF). Stocks of carbon (C) and nitrogen (N) in the whole soil and in physical pools were determined and SOM composition was investigated by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis. Among the pasture environments, AP presented the greatest C and N stocks in soil and in the light fractions. The heavy fraction of BP presented the greatest aromaticity index, and this can be related to the presence of pyrogenic carbon. Concerning soil carbon accumulation, AP represents a sustainable alternative in relation to the practice of vegetation burning in the management of native pastures in southern Brazil. Este estudo investigou a composição química e distribuição da matéria orgânica do solo (SOM) em compartimentos de Oxissolo sob pastagem nativa sem queima há 41 anos (NP), pastagem nativa sem queima há oito anos (BP), pastagem nativa em solo com calcário e adubado, sem queima há 41 anos (AP), e mata nativa (NF). Os estoques de carbono (C) e nitrogênio (N) no solo e nos compartimentos físicos foram determinados e a composição química da SOM foi investigada por espectroscopia de infravermelho com transformada de Fourier (FTIR) e análise termogravimétrica. Entre os ambientes sob pastagem, AP apresentou maiores estoques de C e de N no solo e nas frações leves. A fração pesada de BP apresentou maior índice de aromaticidade, o que pode ser devido à presença de carbono pirogênico. O sistema AP apresenta uma alternativa sustentável para sequestrar carbono em comparação com as práticas de queima da vegetação em sistemas de pastagens nativas no sul do Brazil.

O cultivo de arroz irrigado pode contribuir com a emissão de metano (CH4), em razão das condições anaeróbicas, após o alagamento do solo. Alternativas ao alagamento contínuo da irrigação na cultura do arroz têm sido desenvolvidas a fim de mitigar o efluxo de CH4 para a atmosfera. O objetivo deste estudo foi verificar o efeito do regime de irrigação contínua, intermitente e por banhos no efluxo de CH4 em arroz irrigado. Para tal, foi conduzido um experimento no Departamento de Fitotecnia da Universidade Federal de Santa Maria, durante os anos agrícolas 2007/2008 e 2009/2010. Os tratamentos consistiram em irrigação contínua e intermitente, em 2007/2008, e irrigação contínua, intermitente e por banhos, em 2009/ 2010. A prática da irrigação intermitente é eficiente em abrandar o efluxo de CH4 no cultivo do arroz irrigado, quando as condições climáticas permitem a ausência da lâmina de água durante o cultivo. A eficiência em suavizar o efluxo de CH4 pelo manejo intermitente da irrigação na cultura do arroz depende das condições eletroquímicas do solo, durante a intermitência dos ciclos de alagamento da cultura. Paddy rice fields may contribute to methane (CH4) emission from soil due to anaerobic conditions after flooding. Alternatives to continuous flooding irrigation in rice have been developed to mitigate CH4 efflux into the atmosphere. This study aims to investigate the effects of irrigation managements in the CH4 efflux during the rice growing season. An experiment was carried out at in Santa Maria, Rio Grande do Sul State, Brazil, during 2007/08 and 2009/10 growing seasons. The treatments were continuous flooding and intermittent irrigation in 2007/08 and continuous flooding, intermittent irrigation and flush irrigation in 2009/10. Intermittent irrigation is effective in mitigating CH4 efflux from rice fields when climatic conditions enable water absence during cultivation, but its efficiency depends on the electrochemical soil conditions during the flooding cycles.