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Potassium (K) fertilization guidelines often oversimplify, overlooking factors like soil mineralogy and K application methods. This study aimed to evaluate the influence of K fertilizer rates and application methods on crop yields and the forms of K in soils with different textural and mineralogical features. In 2020, two field trials were conducted to evaluate the impact of varying K rates, added through band or broadcast methods, in Planosol and in Ferralsol. Soybean yield was evaluated in both trials, while flooded rice yield was evaluated only in the Planosol. Soil samples collected from the 0–10 and 10–20 cm layers and soil K content was determined using Mehlich-1, nitric acid (HNO3), and sodium tetraphenylborate. In the Ferralsol, K desorption by HNO3 in the 10–20 cm soil layer was 1.4 times higher the in band application (171 mg kg−1) compared to broadcast method (92 mg kg−1). The Mehlich-1 extractor proved insensitive to detecting K rates in the Planosol (91 and 43 mg kg−1 in the 0–10 and 10–20 cm layers, respectively), while it exhibited responsiveness in the Ferralsol, demonstrating positive increases with K rates. Using a proper chemical extractor is crucial for accurate detection and recovery of applied K in the soil. Grain yields were 4.50 Mg ha−1 for soybeans in the Ferralsol and 9.72 and 5.55 Mg ha−1 for rice and soybeans, respectively, in the Planosol. The findings reveal that applied K distributes into preexisting pools, persisting in the applied location, thereby reducing the anthropogenic K gradient with band reapplication. [ABSTRACT FROM AUTHOR]

Phosphorous is a limiting nutrient in sugarcane cultivated in Argisols in the Northeast of Brazil, and understanding its availability in the soil, as well as determining sufficiency ranges in the plants is essential when recommending levels of phosphorus fertiliser. The aim of this study was to: (i) Define class es for interpreting P availability in Argisols of the Northeast using the Mehlich-1 and Anion Exchange Resin (AER) extractors; (ii) Evaluate P extraction by the same extractors; and (iii) Correlate the P content of the soil with the P content of the plants, and establish sufficiency ranges in the plants. Three field trials were carried out in a sandy (PVAd1), medium (PAdx) and clayey (PVAd2) Argisol, applying the following amounts of P: 0, 40, 80, 120, 160 and 200 kg ha-1 P2O5. The AER extracted more P than did Mehlich-1 from each of the soils. The P content of the classes for interpreting P availability determined by the AER were higher than those determined by Mehlich-1. AER was the best extractor to represent P availability in the Argisol with the clayey texture (PVAd2), and Mehlich-1 in the Argisol with the sandy texture (PVAd1). The ranges of P sufficiency in the leaves of the sugarcane varied between soils, with values of 0.66-0.73 g kg-1 in PVAd1, 0.59-0.69 g kg-1 in PVAd2 and 0.34-0.47 g kg-1 in PAdx. As such, the texture of Argisols cultivated with sugarcane in the Northeast of Brazil should be a criterion for choosing the P extractor used in assessing its availability. [ABSTRACT FROM AUTHOR]

ABSTRACT Phosphorous is a limiting nutrient in sugarcane cultivated in Argisols in the Northeast of Brazil, and understanding its availability in the soil, as well as determining sufficiency ranges in the plants is essential when recommending levels of phosphorus fertiliser. The aim of this study was to: (i) Define classes for interpreting P availability in Argisols of the Northeast using the Mehlich-1 and Anion Exchange Resin (AER) extractors; (ii) Evaluate P extraction by the same extractors; and (iii) Correlate the P content of the soil with the P content of the plants, and establish sufficiency ranges in the plants. Three field trials were carried out in a sandy (PVAd1), medium (PAdx) and clayey (PVAd2) Argisol, applying the following amounts of P: 0, 40, 80, 120, 160 and 200 kg ha-1 P2O5. The AER extracted more P than did Mehlich-1 from each of the soils. The P content of the classes for interpreting P availability determined by the AER were higher than those determined by Mehlich-1. AER was the best extractor to represent P availability in the Argisol with the clayey texture (PVAd2), and Mehlich-1 in the Argisol with the sandy texture (PVAd1). The ranges of P sufficiency in the leaves of the sugarcane varied between soils, with values of 0.66-0.73 g kg-1 in PVAd1, 0.59-0.69 g kg-1 in PVAd2 and 0.34-0.47 g kg-1 in PAdx. As such, the texture of Argisols cultivated with sugarcane in the Northeast of Brazil should be a criterion for choosing the P extractor used in assessing its availability.

There are several methods for determining boron (B) in soil for soil testing purposes, yet variability among methods can lead to inconsistencies in determined concentrations for the same soil sample. The most typical method used to determine B in soil is hot-water B (HWB) extraction, but this method has reduced efficiency when dealing with large sets of soil samples along with other disadvantages such as non-uniformity in the boiling of samples. As a result, universal extractants have become increasingly popular for the extraction of B due to enhanced efficiency in a high throughput laboratory setting. This study uses a Deming regression model to compare the traditional HWB extraction method with two common universal extractants, Mehlich-1 (M1), and Mehlich-3 (M3), for coastal plain sandy soils. Results showed M3-B extractability is consistently higher than M1-B and HWB for all tested soils. The M3 method was then verified for precision using blind extension soil samples. The hot-water method was unsuccessful in producing reliable extractable B concentration in soils with high calcium carbonate and organic matter contents. Results from this study can be used to optimize B determination for high throughput production laboratory settings. [ABSTRACT FROM AUTHOR]

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ABSTRACT Mehlich-1 is the most used method in Brazil for extracting available phosphorus (P) from the soil. Given the heterogeneity of soils in the semi-arid region of the Northeast, and the need for an analytical protocol for P extraction, the Mehlich-1, Olsen and ion-exchange resin methods were compared in samples of ten representative soils taken from the semi-arid region between the valley of the River Piranhas-Açu (Rio Grande do Norte) and the valley of the River Jaguaribe (Ceará), where the soil pH ranges from 4.1 to 8.0. The soil samples received four doses of P based on the phosphate buffering capacity (PBC) of the soils, and were incubated for 30 days. The treatments were divided into randomised blocks, in a 10×4 factorial arrangement of ten soils and four doses of phosphorus, with three replications. Each experimental unit comprised one plastic pot containing 3.0 dm3 of soil, where two maize plants were grown for 31 days in a greenhouse. The P extracted by each method was correlated with the P accumulated in the aerial part of the plants. The mixed-resin and Olsen methods showed the best correlation with the P accumulated in the plants, irrespective of the pH or PBC of the soil. Neutralisation of the acidity of Mehlich-1 was significant in alkaline soils with high levels of CaCO3 equivalent. Mehlich-1 was suitable for strongly acidic soils with a low PBC, however, the use of this extractor in pH neutral to alkaline soils with a high Ca2+ content can overestimate P availability when the soils are rich in P-Ca, or underestimate the availability in soils rich in CaCO3.

The Mehlich-1 extractor is the most used in Brazil, however it extracts low phosphorus (P) levels in soils with high clay levels and iron-bound (Fe) and aluminum (Al) fractions. Thus, we aimed to evaluate the P availability and fertility classes in Yellow Latosol (YL) and Gleysol Haplicum (GH) soils using Mehlich-1, Mehlich-3 and anion exchange resin extractors, as well as to estimate the critical P levels in the soil and in plants for establishing Urochloa humidicola cv. Common. All extractors were efficient in evaluating the availability of P in the soil, however the anion exchange resin showed a high correlation with the P accumulation in the shoot, which can be considered the most efficient method in P extraction. However, we recommend the Mehlich-3 extractor due to its high efficiency in extracting the P linked to the Fe and Al fractions, in addition to being a multi-element extractor. The critical level of P in the soil for establishing U. humidicola by Mehlich-3 in YL is 10.32 mg dm-3, while it is 7.46 mg dm-3 in GH. The critical P level in plants grown in YL is 1.20 mg dm-3, and it is 1.54 mg dm-3 in GH. The estimated phosphate doses can be recommended for cultivating U. humidicola and can serve as a reference for future research on correlating and calibrating P doses. [ABSTRACT FROM AUTHOR]

Increasing interest focuses on utilizing wetlands to reduce nutrient loading to surface waters. The current study examines soil P storage capacity in three treatment wetlands designed to decrease N loading from an agricultural tile drainage system in Illinois. Adjacent farm field and restored floodplain wetland soils were also evaluated. Results demonstrate that wetland soils sequestered P; however, the magnitude of P retention varied significantly across treatment systems and floodplain wetlands related to differences in soil properties. Soil P storage capacity increased in the direction of water flow, but varied across treatment wetlands; soils ranged from P sinks (5.8 ± 1.5 mg P kg−1) to potential P sources (−17.2 ± 2.0 mg P kg−1). Farm fields displayed the highest water soluble P levels (11.3 ± 1.5 mg P kg−1) and represented the largest potential source of P with a mean storage capacity of −48.6 ± 6.8 mg P kg−1. A phosphorus saturation ratio threshold value of 0.10 differentiated between potential P sources and sinks. Findings suggest wetlands receiving P loadings from tile drainage accumulate soil P over time, but maintaining P removal efficiency in treatment wetlands may require periodic management to decrease soil P concentrations via nutrient removal and/or soil amendments. [ABSTRACT FROM AUTHOR]

ABSTRACT In areas cultivated under no-tillage system, the availability of phosphorus (P) can be raised by means of the gradual corrective fertilization, applying phosphorus into sowing furrows at doses higher than those required by the crops. The objective of this work was to establish the amount of P to be applied in soybean crop to increase content of P to pre-established values at the depth of 0.0 to 0.10 m. An experiment was carried out on a clayey Haplorthox soil with a randomized block experimental design distributed in split-split plot, with four replications. Two soybean crop systems (single or intercropped with Panicum maximum Jaca cv. Aruana) were evaluated in the plots. In addition, it was evaluated four P levels (0, 60, 120 and 180 kg ha-1 P2O5) applied in the first year in the split plots; and four P levels (0, 30, 60 and 90 kg ha-1 P2O5) applied in the two subsequent crops in the split-split plot. Contents of P were extracted by Mehlich-1 and Anion Exchange Resin methods from soil samples collected in the split-split plot. It was found that it is necessary to apply 19.4 or 11.1 kg ha-1 of P2O5, via triple superphosphate as source, to increase 1 mg dm-3 of P extracted by Mehlich-1 or Resin, respectively, in the 0.0 to 0.10 m layer of depth. The soil drain P character decreases as the amount of this nutrient supplied in the previous crops is increased.

In comparison with other micronutrients, the levels of nickel (Ni) available in soils and plant tissues are very low, making quantification very difficult. The objective of this paper is to present optimized determination methods of Ni availability in soils by extractants and total content in plant tissues for routine commercial laboratory analyses. Samples of natural and agricultural soils were processed and analyzed by Mehlich-1 extraction and by DTPA. To quantify Ni in the plant tissues, samples were digested with nitric acid in a closed system in a microwave oven. The measurement was performed by inductively coupled plasma/optical emission spectrometry (ICP-OES). There was a positive and significant correlation between the levels of available Ni in the soils subjected to Mehlich-1 and DTPA extraction, while for plant tissue samples the Ni levels recovered were high and similar to the reference materials. The availability of Ni in some of the natural soil and plant tissue samples were lower than the limits of quantification. Concentrations of this micronutrient were higher in the soil samples in which Ni had been applied. Nickel concentration differed in the plant parts analyzed, with highest levels in the grains of soybean. The grain, in comparison with the shoot and leaf concentrations, were better correlated with the soil available levels for both extractants. The methods described in this article were efficient in quantifying Ni and can be used for routine laboratory analysis of soils and plant tissues.

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).

The accumulation of potentially toxic elements (PTEs) in the soil can pose risks to human health, and precise risk assessment dealing with the production and consumption of plants is required. The 0.43 M of nitric acid (HNO3) solution was suggested by the International Organization for Standardization for reactive fraction of PTEs in the soil. The efficiency of some extractors was evaluated in tropical soils. Contents of barium (Ba), cadmium (Cd), copper (Cu), nickel (Ni) and zinc (Zn) were extracted in accordance with the methods of Environmental Protection Agency (EPA) 3051A, Aqua Regia, Diethylenetriaminepentaacetic acid (DTPA), Mehlich-1, Mehlich-3, 0.43 M HNO3 and 0.01 M of calcium chloride (CaCl2), and these contents correlated with the contents of PTEs in roots, shoots, and fruits of vegetables. Mehlich-3 had the highest correlation with Ni and Zn contents extracted by the plants. Contents extracted with 0.43 M HNO3 had high correlation with the amounts extracted by DTPA and Mehlich-3, as well as with the amounts of PTEs accumulated by plants. [ABSTRACT FROM AUTHOR]

In Brazil, a steady increase in phosphorus (P) fertilizer application and agricultural intensification has been reported for recent decades. The concomitant P accumulation in soils potentially threatens surface water bodies with eutrophication through diffuse P losses. Here, we demonstrated the applicability of a soil type-independent approach for estimating the degree of P saturation (DPS; a risk parameter of P loss) by a standard method of water-soluble phosphorus (WSP) for two major soil types (Oxisols, Entisols) of the São Francisco catchment in Brazil. Subsequently, soil Mehlich-1P (M1P) levels recommended by Brazilian agricultural institutions were transformed into DPS values. Recommended M1P values for optimal agronomic production corresponded to DPS values below critical thresholds of high risks of P losses (DPS = 80%) for major crops of the catchment. Higher risks of reaching critical DPS values due to P accumulation were found for Entisols due to their total sorption capacities being only half those of Oxisols. For complementary information on soil mineralogy and its influence on P sorption and P binding forms, Fourier transformation infrared (FTIR) spectroscopic analyses were executed. FTIR analyses suggested the occurrence of the clay minerals palygorskite and sepiolite in some of the analyzed Entisols and the formation of crandallite as the soil specific P binding form in the investigated Oxisols. Palygorskite and sepiolite can enhance P solubility and hence the risk of P losses. In contrast, the reshaping of superphosphate grains into crandallite may explain the chemical processes leading to previously observed low dissolved P concentrations in surface runoff from Oxisols. To prevent high risk of P losses, we recommend avoiding superficial fertilizer application and establishing environmental thresholds for soil M1P based on DPS. These measures could help to prevent eutrophication of naturally oligotrophic surface waters, and subsequent adverse effects on biodiversity and ecosystem function. [ABSTRACT FROM AUTHOR]

Zinc is an important micronutrient to plant growth, but when present in large quantities it can become a toxic element to plants. This study was aimed to evaluate the growth, concentration, accumulation and availability of Zn to forage grasses (Megathyrsus maximus cvs. Aruana and Tanzania, Urochloa brizantha cvs. Xaraés and Marandu and Urochloa decumbens cv. Basilisk) cultivated in Zn contaminated soils. The experiments were conducted under greenhouse conditions over a 90-day evaluation period, and Zn rates were 0, 100, 300 and 900 mg kg−1 of soil. The Zn rates in soil caused growth reduction in all evaluated forage grasses. The cultivar Aruana was generally more tolerant to Zn, while the Marandu was generally more susceptible to the addition of Zn. The cultivar Aruana proved to be superior to others due to its higher growth and higher critical level toxicity of Zn. None of the forage grasses evaluated can be considered a Zn hyperaccumulator. The extraction order was DTPA at pH 7.3 < Mehlich-1 < USEPA 3051 < USEPA 3052 in the soil independent of forage grasses cultivation. The USEPA 3051 extractor was similar to Mehlich-1 in predicting the availability of Zn in soil. [ABSTRACT FROM AUTHOR]

O P tem baixa mobilidade no solo resultando em altas concentrações nas regiões adjacentes aos grânulos de fertilizantes fosfatados. Isso pode interferir na disponibilidade de P e na composição química do solo nesses locais. O objetivo deste estudo foi avaliar a composição química do solo e a mobilidade de P nas adjacências de regiões fertilizadas com fosfatos de amônio ou de cálcio, em solos ácidos. Este trabalho foi realizado em 2009, com amostras de dois solos catarinenses. Os tratamentos consistiram de combinações de superfosfato triplo (SFT) ou de fosfato diamônico (DAP) com KCl, além de um controle somente com KCl. As unidades experimentais foram constituídas por colunas de PVC com 10,0 cm de diâmetro e 12,0 cm de comprimento, preenchidas com 1,60 kg de solo (base úmida). Foram aplicadas quantidades equivalentes a 200 kg ha-1 de P2O5 e de K2O, considerando a área de contato superficial de solo de 10(4) m². Tentando simular a aplicação localizada de fertilizantes, essas quantidades foram estipuladas para contatarem com 357 m² de solo, tendo sido aplicadas 10,47; 9,56; e 7,33 g por coluna de SFT, DAP e KCl respectivamente, numa área de contato de 0,00785 m². Quarenta e cinco dias após a aplicação dos fertilizantes, as colunas foram desmontadas e o solo foi analisado a cada centímetro distante do local de aplicação dos grânulos. O P foi quantificado pelos métodos Mehlich-1 e da resina trocadora de ânions (RTA), numa sequencia de nove extrações cumulativas. O DAP aumentou o pH e diminuiu o Al nas adjacências dos grânulos, porém o SFT aumentou Ca e Mg. A quantidade cumulativa extraída de P variou com o tipo de adubo fosfatado, a distância dos grânulos, o tipo de solo e o método de extração. Na camada distante até 1,0 cm dos adubos, o SFT proporcionou os maiores valores de P, que chegaram a atingir 10.276 mg dm-3; nas duas camadas seguintes (1,0-2,0 e 2,0-3,0 cm), isso normalmente ocorreu com o DAP. O Mehlich-1 quantificou sempre mais P do que a RTA nas adjacências dos fertilizantes fosfatados. A movimentação do P nos dois solos ocorreu até o quarto centímetro distante do local de aplicação dos adubos, e a composição química nessas adjacências variou com o fertilizante fosfatado, o tipo de solo, o método de extração e a distância dos grânulos, mas necessita ser mais bem estudada.

Em muitos laboratórios de análises de solos, o ácido 1-Amino-2-naftol-4-sulfônico (ANS) é usado como agente redutor para determinação do P por espectrometria de UV/Visível. Porém, devido aos riscos à saúde dos laboratoristas, uma alternativa é o uso do ácido ascórbico (AA). Entretanto, modificações no protocolo de análise podem induzir a variações nos resultados, havendo a necessidade de padronizá-las e calibrá-las. O objetivo do trabalho foi avaliar o ANS e AA nos extratos de Mehlich-1 e 3 nos intervalos de 15, 30, 45, 60 e 120min de reação. Não houve diferença na concentração de P determinado com ambos redutores quando comparados dentro de cada extrator. O ácido ascórbico pode substituir a solução ANS para determinação de P e o intervalo de tempo de reação sugerido para a quantificação colorimétrica é de 30 a 60min, para ambos redutores.

The objectives of this study were to assess the concentrations of available phosphorus (P) extracted using the Mehlich-1 (M1), ion exchange resin (IER) and modified Morgan (MM) methods after 36 months of experimentation with the application of phosphates in a crop-livestock integration system (CLIS). Moreover, this study aimed to assess which extraction method provides the best correlation of P concentrations with the maize crop attributes. The treatments consisted of applying annual doses of P2O5 on the soil surface of the total area during the sowing of winter forage crops in the form of triple superphosphate (TSP), rock phosphate (RP) or magnesium thermophosphate (MTP). After 36 months of experimentation, soil samples were collected from the 0-5, 5-10, 10-15 and 15-20 cm layers to assess the concentrations of available P. The dry matter yield (DMY), the grain yield (GY), the accumulation of phosphorus in the dry matter (P-DM) and the export of phosphorus (P-Ex) were quantified in maize. The IER method extracted greater amounts of available P, followed by the M1 and MM extractions. The treatments that included the application of TSP and either the M1 or IER extractions had similar efficacies when correlated with the DMY, GY, P-DM and P-Ex attributes of maize. The P extracted by the IER was most correlated with P-DM and P-Ex for the water-insoluble P sources (RP and MTP). The MM solution was ineffective at predicting the availability of P for maize grown in a soil with that had received varying doses and sources of P applications in a CLIS.

We assessed the sensitivity of mixed exchange resin (MER) and Mehlich-3 (M3) to calcium-bound phosphate (Ca-P) in Oxisols. These methods were compared with Mehlich-1 (M1) and anion exchange resin (AER), which have high and low sensitivity, respectively, to this soil P form. We used maize (Zea mays L.) as a test plant. Three samples from two Oxisols were treated with five ratios of Triple Superphosphate—TS and Bayóvar Phosphate Rock—BPR (0 + 100; 25 + 75, 50 + 50, 75 + 25 and 100 + 0% TS + BPR). The MER extracted more P than AER and M3 at the highest BPR:TS ratios (high Ca-P) and similar quantities at the higher TS:BPR ratios (low Ca-P) for two soil samples. Unlike M1-extracted P, M3-P, AER-P, and MER-P positively correlated with maize dry matter production and P uptake. Mehlich-3 and MER were suitable to assess P availability in high Ca-P Oxisols. [ABSTRACT FROM AUTHOR]

ABSTRACT Mehlich-1 soil extract is currently used in Rio Grande do Sul (RS) and Santa Catarina (SC) States, in Brazil, to evaluate soil phosphorus available to plants and Mehlich-1 is sensitive to soil buffering capacity. This limitation is overcome partly by soil separation into buffering classes based on soil clay content. However, soil clay content has some technical and operational limitations, such as the underestimation of soil clay levels in soils under no-till. The aim of this study was to evaluate the remaining phosphorus (P-rem) compared to soil clay content as an index of the buffering capacity in soils of RS. The relationship between P-rem and soil clay content was assessed using 200 soil samples from a wide range of locations across the state. In 20 representative soil types, P-rem, soil clay content, P maximum adsorption capacity, total and pedogenic Fe contents, amount of P2O5 needed to increase soil P in 1 mg kg-1 extracted by Mehlich-1 and -3 methods and P capacity factor were determined. Furthermore, a pot experiment was carried out with plants to determine soil P content extracted by Mehlich-1 and -3 at the maximum technical efficiency (MET) and the maximum absorption efficiency (MEA). Correlation analyses were performed between P-rem and soil clay content and, with the attributes of soils involving the P buffering capacity. The relationship between P-rem and soil clay content was described as a decreasing exponential function; however, the adjustment was not adequate to propose critical levels for P-rem. The P-rem index was superior to soil clay index in practically all relationships with the attributes related to the soil buffering capacity of the soils. In some cases, the indexes were similar; however, P-rem was not lower than the soil clay content in any case. The P-rem is a more reliable index to represent soil buffering capacity than the soil clay content in soils from RS, and P-rem might be used to implement soil classes for Mehlich-1 and Mehlich-3 determinations of soil P.

No Brasil, com a expansão da silvicultura clonal, o plantio de materiais genéticos mais produtivos e exigentes nutricionalmente tem aumentado o aparecimento de sintomas de deficiência de micronutrientes, principalmente de B, e, mais recentemente, de Cu e de Zn, sobretudo em áreas de Cerrado. Este trabalho teve por objetivo avaliar três métodos de determinação da disponibilidade de Zn (Mehlich-1, Mehlich-3 e DTPA pH 7,3) para mudas de eucalipto cultivadas em casa de vegetação, em amostras de seis solos de Cerrado, bem como a influência de propriedades do solo na eficiência desses extratores. Os tratamentos foram arranjados no esquema fatorial 6 x 5, correspondendo a seis solos e cinco doses de Zn (0, 2,5, 5, 10 e 20 mg dm-3), com quatro repetições, em blocos ao acaso. Os níveis críticos de Zn em solos de Cerrado, para o crescimento de mudas de eucalipto, são iguais ou inferiores a 0,23 e 0,05 mg dm-3, pelos extratores Mehlich-1 e DTPA, respectivamente. Os teores de Zn no solo pelos três extratores, assim como os teores e conteúdo na planta, aumentam com a elevação das doses adicionadas de Zn e são altamente correlacionados entre si. A avaliação da disponibilidade de Zn para mudas de eucalipto pode ser feita com qualquer um dos três extratores; entretanto, o Mehlich-1 é o mais recomendado, pela facilidade operacional deste método em relação aos outros e por ele já ser usado na grande maioria dos laboratórios do país.

In studies on the evaluation of methodologies for the analysis of soil, phosphorus (P) has been the single most studied aspect, due to the complexity of this dynamic element in soil. However, these studies have been limited regarding soil conditions in Paraná. The present study aimed to evaluate the efficiency of the Mehlich-1, Mehlich-3 and ion exchange resin methods in the evaluation of available P for soybean (Glycine max) in the soils of Paraná State. Twelve soil samples collected from the upper 0-20 cm were planted with soybean for a period of 42 days in the greenhouse. The ability to extract soil P followed the order of decreasing average amount of extracted P: Mehlich-3 > resin > Mehlich-1. The correlation coefficients between the content of P extracted by Mehlich-1, Mehlich-3 and resin and the amount of P accumulated in the plants were 0.86, 0.90 and 0.93, respectively. Mehlich-1, Mehlich-3 and resin showed similar efficiency in the evaluation of P availability to plants and, under conditions of natural fertility and in soils that had received no application of poorly natural reactive phosphates, can be used to quantify the concentrations of P in the soils of Paraná State. Nos estudos de avaliação de metodologias de análise de solo, o fósforo (P) tem sido o elemento mais estudado, em decorrência da complexidade da dinâmica do elemento no solo. No entanto, estes estudos são escassos para as condições de solos paranaenses. O presente estudo teve como objetivo avaliar a eficiência dos extratores Mehlich-1, Mehlich-3 e resina de troca iônica na avaliação do P disponível para plantas de soja (Glycine max) em solos do Estado do Paraná. Amostras de doze solos coletadas da camada de 0-20 cm de profundidade foram cultivadas com plantas de soja por um período de 42 dias, em casa de vegetação. A capacidade de extração de P dos solos seguiu a seguinte ordem decrescente da quantidade média de P extraído: Mehlich-3 > resina > Mehlich-1. Os coeficientes de correlação entre o teor de P extraído pelo Mehlich-1, Mehlich-3 e resina e as quantidades de P acumulada nas plantas foram, respectivamente, de 0,86, 0,90 e 0,93. Os extratores Mehlich-1, Mehlich-3 e resina de troca iônica apresentaram eficiência semelhante na avaliação da disponibilidade de P às plantas e, em condições de fertilidade natural e em solos que não receberam aplicação de fosfatos naturais poucos reativos, podem ser utilizados para quantificar os teores de P em solos do Estado do Paraná.

Foram comparadas as concentrações de Na, K e P em extratos de solos, obtidas por um método de extração convencional, no qual é utilizada uma razão solo:extrator (Mehlich-1) de 1:10, com aquelas encontradas utilizando uma razão solo:extrator (Mehlich-1) de 1:5. Também, foram comparados os resultados obtidos por técnicas de quantificação convencionais, nas quais Na e K são quantificados por fotometria de chama e P por espectrofotometria de absorção molecular, com aqueles encontrados por espectrometria de emissão óptica com plasma indutivamente acoplado (ICP OES). Foram analisadas 15 amostras de solo brasileiro. No estudo de repetibilidade aplicado a todos os resultados, os maiores CVs foram encontrados para P e Na, principalmente quando as concentrações dos analitos foram menores (< 9 mg dm-3 para P e < 10 mg dm-3 para Na). Esse fato foi devido provavelmente à heterogeneidade dos extratos, que continham partículas coloidais. Filtração ou centrifugação em vez de decantação dos extratos provavelmente resultaria em menores CVs. No estudo de reprodutibilidade, realizado para três amostras, foram obtidos resultados não reprodutíveis somente para K em uma amostra. Todos os resultados obtidos por ICP OES foram semelhantes aos obtidos por espectrofotometria de absorção molecular UV-Vis. e fotometria de chama, indicando que a primeira técnica foi adequada para determinação de Na, K e P nos extratos de solos tropicais obtidos com solução de Mehlich-1. Os resultados de Na, K e P obtidos com razão solo:extrator de 1:5 foram estatisticamente diferentes daqueles em que se utilizou razão solo:extrator de 1:10. A maioria dos resultados obtidos com razão solo:extrator de 1:5 foi menor que os obtidos com razão solo:extrator 1:10, sobretudo nas amostras com concentrações de analitos mais elevadas. Portanto, para estudos comparativos envolvendo macronutrientes, deve-se utilizar o método convencional com razão solo:extrator de 1:10.

Considerations on the interactions of P in the soil-plant system have a long history, but are still topical and not yet satisfactorily understood. One concern is the effect of liming before or after application of soluble sources on the crop yield and efficiency of available P under these conditions. The aim of this study was to evaluate the effect of soil acidity on availability of P from a soluble source, based on plant growth and chemical extractants. Nine soil samples were incubated with a dose of 200 mg kg-1 P in soil with different levels of previously adjusted acidity (pH H2O 4.5; 5.0; 5.5; 6.0 and 6.5) and compared to soils without P application. After 40 days of soil incubation with a P source, each treatment was limed again so that all pH values were adjusted to 6.5 and then sorghum was planted. After the first and second liming the P levels were determined by the extractants Mehlich-1, Bray-1 and Resin, and the fractionated inorganic P forms. In general, the different acidity levels did not influence the P availability measured by plant growth and P uptake at the studied P dose. For some soils however these values increased or decreased according to the initial soil pH (from 4.5 to 6.5). Plant growth, P uptake and P extractable by Mehlich-1 and Bray-1 were significantly correlated, unlike resin-extractable P, at pH values raised to 6.5. These latter correlations were however significant before the second liming. The P contents extracted by Mehlich-1 and Bray-1 were significantly correlated with each other in the entire test range of soil acidity, even after adjusting pH to 6.5, besides depending on the soil buffering capacity for P. Resin was also sensitive to the properties that express the soil buffering capacity for P, but less clearly than Mehlich-1 and Bray-1. The application of triple superphosphate tended to increase the levels of P-Al, P-Fe and P-Ca and the highest P levels extracted by Bray-1 were due to a higher occurrence of P-Al and P-Fe in the soils.Considerações históricas sobre a interação do P no sistema solo-planta são ainda atuais e não satisfatoriamente resolvidas. Uma delas diz respeito ao efeito da calagem antes ou após a aplicação de fontes solúveis de P no rendimento das culturas e na eficiência do P disponível nessas condições. O objetivo desse trabalho foi avaliar o efeito da acidez do solo sobre a disponibilidade de P de uma fonte solúvel, por meio do crescimento de plantas e extratores químicos. Amostras de nove solos foram incubadas com uma dose de P (200 mg kg-1) em diferentes níveis de acidez previamente ajustados (pH H2O 4,5; 5,0; 5,5; 6,0 e 6,5), comparativamente à não-adição de P nos solos. Após 40 dias de incubação do solo com a fonte de P, cada tratamento recebeu uma nova calagem de maneira que todos os valores de pH fossem elevados igualmente para 6,5 e, após essa etapa, foi cultivado sorgo. Após a primeira e a segunda calagem foram determinados os teores de P pelos extratores Mehlich-1, Bray-1 e Resina e, realizado o fracionamento das formas inorgânicas de P. De modo geral, para a dose de P aplicada, os diferentes níveis de acidez não alteraram a disponibilidade deste nutriente, medida pelo crescimento de plantas e pelo P absorvido, porém para alguns solos houve aumentos ou decréscimos dessas medidas com o aumento inicial do pH do solo (de 4,5 a 6,5). Correlações significativas foram encontradas entre crescimento de planta, P absorvido e o P-extraível pelo Mehlich-1 e pelo Bray-1, mas não para a Resina quando todos os valores de pH foram elevados para 6,5. Todavia, essas mesmas correlações foram significativas antes da realização da segunda calagem. Os teores de P pelos extratores Mehlich-1 e Bray-1 correlacionam-se significativamente entre si para toda a faixa de acidez do solo testada, inclusive após o ajuste do pH para 6,5, além de terem se mostrado dependentes do poder tampão de P do solo. A Resina também se mostrou sensível à propriedades que refletem o poder tampão de P no solo, porém de maneira menos expressiva que o Mehlich-1 e o Bray-1. Com a aplicação do superfosfato triplo ocorreu uma tendência de aumentos nos teores de P-Al, P-Fe e P-Ca e, os maiores teores de P recuperados pelo Bray-1 deve-se à maior ocorrência de P-Al e P-Fe nos solos.

The eutrophication of aquifers is strongly linked to the mobility of P in soils. Although P mobility was considered irrelevant in a more distant past, more recent studies have shown that P, both in organic (Po) and inorganic forms (Pi), can be lost by leaching and eluviation through the soil profile, particularly in less weathered and/or sandier soils with low P adsorption capacity. The purpose of this study was to determine losses of P forms by leaching and eluviation from soil columns. Each column consisted of five PVC rings (diameter 5 cm, height 10 cm), filled with two soil types: a clayey Red-Yellow Latosol and a sandy loam Red-Yellow Latosol, which were exposed to water percolation. The soils were previously treated with four P rates (as KH2PO4 ) to reach 0, 12.5, 25.0 and 50 % of the maximum P adsorption capacity (MPAC). The P source was homogenized with the whole soil volume and incubated for 60 days. After this period the soils were placed in the columns; the soil of the top ring was mixed with five poultry litter rates of 0, 20, 40, 80, and 160 t ha-1 (dry weight basis). Treatments consisted of a 4 x 5 x 2 factorial scheme corresponding to four MPAC levels, five poultry litter rates, two soils, with three replications, arranged in a completely randomized block design. Deionized water was percolated through the columns 10 times in 35 days to simulate about 1,200 mm rainfall. In the leachate of each column the inorganic P (reactive P, Pi) and organic P forms (unreactive P, Po) were determined. At the end of the experiment, the columns were disassembled and P was extracted with the extractants Mehlich-1 (HCl 0.05 mol L-1 and H2SO4 0.0125 mol L-1) and Olsen (NaHCO3 0.5 mol L-1; pH 8.5) from the soil of each ring. The Pi and Po fractions were measured by the Olsen extractant. It was found that under higher poultry litter rates the losses of unreactive P (Po) were 6.4 times higher than of reactive P (Pi). Both the previous P fertilization and increasing poultry litter rates caused a vertical movement of P down the soil columns, as verified by P concentrations extracted by Mehlich-1 and NaHCO3 (Olsen). The environmental critical level (ECL), i.e., the P soil concentration above which P leaching increases exponentially, was 100 and 150 mg dm-3 by Mehlich-1 and 40 and 60 mg dm-3 by Olsen, for the sandy loam and clay soils, respectively. In highly weathered soils, where residual P is accumulated by successive crops, P leaching through the profile can be significant, particularly when poultry litter is applied as fertilizer.A eutroficação de aquíferos está fortemente ligada à mobilidade de P nos solos. Embora essa mobilidade tenha sido considerada, num passado mais distante, como inexpressiva, estudos mais recentes têm mostrado que o P, tanto na forma orgânica (Po) quanto na inorgânica (Pi), pode se perder por percolação e eluviação de partículas através do perfil de solos, particularmente naqueles menos intemperizados e, ou, arenosos com menor adsorção de P. O objetivo deste trabalho foi verificar perdas por lixiviação e eluviação de formas de P em colunas de solos, constituídas por cinco anéis de PVC sobrepostos, com 5 cm de diâmetro e 10 cm de altura cada, submetidas a fluxos de percolação de água. Foram utilizadas amostras de dois Latossolos Vermelho-Amarelos, texturas argilosa e média. Os solos receberam, previamente, quatro doses de P na forma de KH2PO4, correspondentes a 0; 12,5; 25 e 50 % da capacidade máxima de adsorção de P (CMAP), homogeneizadas com todo o volume de solo das colunas e deixados em incubação por 60 dias. No anel superior, aplicou-se, homogeneamente, cama de aviário nas doses equivalentes a 0, 20, 40, 80 e 160 t ha-1; com base no peso do material seco. O experimento foi constituído pelo esquema fatorial: quatro níveis da CMAP, cinco doses de cama de aviário, dois solos, com três repetições dispostas em blocos casualizados. As colunas foram submetidas a 10 percolações com água deionizada, em duas aplicações semanais, durante 35 dias, de modo que se atingisse um volume aproximado de 1.200 mm. Nos lixiviados de cada coluna, foram determinados: P reativo (Pi) e P não reativo (Po). No final do experimento, o P no solo de cada anel foi extraído com Mehlich-1 e com NaHCO3 0,5 mol L-1; pH 8,5 (Olsen), sendo determinadas, para este último extrator, as formas Pi e Po. Com o aumento das doses aplicadas de cama de aviário, as perdas de P por lixiviação foram, em média, 6,4 vezes maiores na forma de P não reativo (Po) que no P-reativo (Pi). Tanto a fertilização mineral prévia com P quanto a aplicação de doses crescentes de cama de aviário causaram movimentação descendente de P nas colunas de solo, extraído tanto pelo Mehlich-1 quanto pelo NaHCO3 (Olsen). O nível crítico ambiental (NCA), teor de P disponível no solo acima do qual a percolação de P-reativo aumenta exponencialmente, foi de 100 e 150 mg dm-3 para o Mehlich-1 e de 40 e 60 mg dm-3 para o Olsen, para os solos de textura média e argilosa, respectivamente. Em solos intemperizados, com acúmulo de P residual ao longo dos cultivos, as perdas de P por lixiviação no perfil podem ser significativas, de modo particular quando fertilizados com cama de aviário.

As quantidades extraídas de cobre (Cu) e de zinco (Zn) pelas soluções de HCl 0,1mol L-1 (HCl) foram comparadas com as extraídas pelas soluções de Mehlich-1 (M1) e de Mehlich-3 (M3). Foram utilizadas 130 amostras de solo representando as principais áreas agrícolas do Estado do Rio Grande do Sul, as quais foram extraídas do banco de solos do Laboratório de Análises de Solo da Universidade Federal do Rio Grande do Sul. A correlação entre as quantidades extraídas pelos métodos indicou alto grau de associação e de significância. A quantidade de Cu extraída pela solução de M3, em média, não diferiu do HCl. A quantidade extraída de Zn pela solução de M3, entretanto, foi inferior à extraída por HCl. As quantidades extraídas de Cu e Zn pelas soluções de HCl e de M1 não diferiram estatisticamente. As soluções de M1 e de M3 são eficientes para a extração multielementar simultânea de Cu e Zn dos solos e são alternativas viáveis para serem utilizadas em laboratórios de análises de solo dos Estados do Rio Grande do Sul e de Santa Catarina.Copper (Cu) and zinc (Zn) amounts extracted with 0.1molar L-1 HCl (HCl) for the most representative soil types of Rio Grande do Sul State (Brazil) were compared with those extracted with Mehlich-1 (M3) and Mehlich-3 (M3) solutions. The nutrients' amounts extracted by different methods indicated high correlation degree. The M3 solution extracted similar copper amounts than HCl; however, lower amounts of Zn. The M1 and M3 solutions are efficient for simultaneous multielement extraction and can be used in soil testing laboratories for RS and SC states.

The amounts of macro (P, K, Ca and Mg) and micronutrients (Cu and Zn) extracted with the Mehlich-1 (M1) solution, by the 1.0 mol L-1 KCl (KCl) and with the 0.1 mol L-1 HCl (HCl) for representative soil types of the Rio Grande do Sul state (Brazil) were compared with those extracted with the Mehlich-1 solution determined with the inductively coupled plasma optical emission spectroscopy (ICP). The amounts of nutrients extracted by the different methods showed high correlation coefficients. On average, the Mehlich-1 solution extracted similar amounts of P, determined with colorimetric and ICP methods, and, K determined with emission and ICP. The amounts of Ca and Mg extracted with the Mehlich-1 solution, determined by ICP, were similar to those extracted with the KCl solution determined by the atomic absorption spectrophotometry. The amounts of Cu and Zn extracted with the Mehlich-1 solution, determined by the ICP, were higher than those extracted with the 0.1 mol L-1 HCl determined by the atomic absorption spectrophotometry. The results indicate that the Mehlich-1 solution and ICP can be used for simultaneous multielement extraction and determination for Southern Brazilian soils. However, a conversion factor for values interpretation is needed. The use of the conversion factor to determine the K availability index in soils is adequate and does not affect the K recommendations for crops in southern Brazilian soils.As quantidades de macro (P, K, Ca e Mg) e micronutrientes (Cu e Zn) extraídos com a solução de Mehlich-1 (M1), por KCl 1,0 mol L-1 (KCl) e com o HCl 0,1 mol L-1 (HCl), em solos representativos do Rio Grande do Sul, foram comparadas com as quantidades de nutrientes extraídos com a solução de Mehlich-1 determinados por espectrofotometria de emissão ótica por plasma induzido (ICP-OES). Os teores de nutrientes extraídos pelos diferentes métodos tiveram alto grau de correlação. Em média, a solução de Mehlich-1 extraiu quantidades semelhantes de P determinado por colorimetria e por ICP, bem como de K determinado por emissão e ICP. Os teores de Ca e Mg extraídos com a solução de Mehlich-1, determinados por ICP, foram semelhantes aos dos extraídos com a solução de KCl determinada por espectrofotometria de absorção atômica. Os teores de Cu e Zn extraídos com a solução de Mehlich-1, determinados por ICP, foram maiores do que os extraídos com a solução de HCl determinada por espectrofotometria de absorção atômica. Os resultados indicam que a solução de Mehlich-1 e o ICP podem ser usados para extração e determinação multielementar simultânea de solos do sul do Brasil, porém o uso de um fator de conversão para interpretação de valores é necessário em alguns casos. O uso do fator de conversão para determinar o índice de disponibilidade de K no solo é adequado e não altera as recomendações de K para as culturas.

The deficiency or excess of micronutrients has been determined by analyses of soil and plant tissue. In Brazil, the lack of studies that would define and standardize extraction and determination methods, as well as lack of correlation and calibration studies, makes it difficult to establish limits of concentration classes for analysis interpretation and fertilizer recommendations for crops. A specific extractor for soil analysis is sometimes chosen due to the ease of use in the laboratory and not in view of its efficiency in determining a bioavailable nutrient. The objectives of this study were to: (a) evaluate B concentrations in the soil as related to the fertilizer rate, soil depth and extractor; (b) verify the nutrient movement in the soil profile; (c) evaluate efficiency of Hot Water, Mehlich-1 and Mehlich-3 as available B extractors, using sunflower as test plant. The experimental design consisted of complete randomized blocks with four replications and treatments of five B rates (0, 2, 4, 6, and 8 kg ha-1) applied to the soil surface and evaluated at six depths (0-0.05, 0.05-0.10, 0.10-0.15, 0.15-0.20, 0.20-0.30, and 0.30-0.40 m). Boron concentrations in the soil extracted by Hot Water, Mehlich-1 and Mehlich-3 extractors increased linearly in relation to B rates at all depths evaluated, indicating B mobility in the profile. The extractors had different B extraction capacities, but were all efficient to evaluate bioavailability of the nutrient to sunflower. Mehlich-1 and Mehlich-3 can therefore be used to analyze B as well as Hot Water.A deficiência ou o excesso de micronutrientes tem sido observada por meio de análises de solo e de tecido vegetal. No Brasil, a falta de estudos para definição e padronização de método de extração e determinação, assim como a falta de estudos sobre correlação e calibração, dificulta o estabelecimento de limites de classes de teores para a interpretação das análises e recomendações de adubação para as culturas. A opção por determinado extrator para a análise de solos, em algumas situações, ocorre em razão da facilidade de execução no laboratório e não devido à sua eficiência em determinar o nutriente biodisponível. Os objetivos deste trabalho foram: avaliar o teor de B no solo em função da dose do fertilizante, da profundidade do solo e do extrator; verificar a movimentação do nutriente no perfil do solo; e avaliar a eficiência da Água Quente, Mehlich-1 e Mehlich-3 como extratores de B disponível, tendo o girassol como planta-teste. O delineamento experimental foi em blocos completos ao acaso com quatro repetições, e os tratamentos, compostos por cinco doses de B (0, 2, 4, 6 e 8 kg ha-1), aplicadas na superfície do solo e avaliadas em seis profundidades (0 a 0,05, 0,05 a 0,10, 0,10 a 0,15, 0,15 a 0,20, 0,20 a 0,30 e 0,30 a 0,40 m). Os teores de B no solo, extraídos pelos extratores Água Quente, Mehlich-1 e Mehlich-3, aumentaram linearmente em função das doses de B, em todas as profundidades avaliadas, indicando que ele apresenta mobilidade no perfil. Os extratores foram diferentes na capacidade de extração do B, mas eficientes na avaliação da biodisponibilidade do nutriente para o girassol. Portanto, o Mehlich-1 e o Mehlich-3 podem ser utilizados na análise de B, assim como a Água Quente.

As soluções extratoras multielementares possibilitam avaliar a disponibilidade de vários nutrientes de plantas no mesmo extrato; dentre estes o P merece especial atenção. As soluções Mehlich-1 (M1) e Mehlich-3 (M3) enquadram-se nesta categoria. Neste estudo, foram comparados os teores de P extraídos por estas soluções em 360 amostras de solos do Estado do Rio Grande do Sul. Os coeficientes de correlação entre os teores de P extraído pelas mesmas indicaram alto grau de associação e de significância. Os teores de P extraído pela solução Mehlich-3 foram, em média, 50 % maiores que os extraídos pela solução Mehlich-1. O teor de argila, entretanto, influenciou a capacidade extrativa de P pela solução Mehlich-3, sendo necessária uma tabela de ajuste para a interpretação dos valores do P extraído por esta solução.Multielement soil extractant solutions are used by several soil testing laboratories to determine the plant availability of several nutrients by the same extractant, to decrease costs and labor. The Mehlich-1 (M1) and Mehlich-3 (M3) solutions are often used for this purpose. In this study, they were used to evaluate soil P availability using 360 soil samples of the State of Rio Grande do Sul (Southern Brazil). The correlation coefficients between the P concentrations extracted by these solutions were strongly associated and highly significant. The P concentrations extracted by the M3 solution were on average 50 % higher than those extracted by M1. The soil clay content affected the P extraction capacity of the M3 solution, requiring an adjustment table for the interpretation of the P value by this method, as proposed here.

Trace elements are potentially toxic to the environment. Their toxicity in soils relies on their type of chemical associations. Hence it is important to determine the chemical form they occur in the soils in order to assess their quantities. The objective the present work was to evaluate the possibility of using the concentrations of Cu and Zn in different soil fractions and the total concentration as predictors of their quantification by comparing the classical extractants DTPA, Mehlich-1 and HCl. Comparisons were made also with the concentrations of absorbed by rice and soybean in contaminated soil. Seven soil samples with a different degree of contamination were studied using a randomized experimental design, with four replicates. By using an ICP-OES we analyzed the concentrations of Cu and Zn in the diagnostic leafs, at the end of the cycle (LCE) and several of its content in the soil: available extracted with the DTPA, Mehlich-1 and HCl extractants, soluble+exchangeable contents, bound to organic matter, to oxides and the total content. For both, soybean and rice, the concentrations of Cu and Zn extracted from the sequential extraction was found to be correlated with the concentration in LCE. For soybean, Zn concentration extracted with DTPA was correlated with the total concentration, while Cu concentration extracted with three extractors, DTPA, Mehlich-1 and HCl, correlated with the total concentration, probably due to the high concentration of Cu and Zn in this soil. For rice, both Cu and Zn concentration as extracted by the three extracting solutions correlated with the concentration of all the fractions and with the total concentration.Os elementos traços são potencialmente tóxicos para o meio ambiente. Estas toxicidades dependem de suas associações químicas. Por isso a determinação da forma química destes elementos no solo é importante para quantificá-lo. O objetivo do presente trabalho foi avaliar a possibilidade de se utilizar teores de Cu e Zn nas diferentes frações do solo para prognosticar suas disponibilidades. Para isso, compararam-se as mesmas com soluções extratoras clássicas, como DTPA, Mehlich-1 e HCl, e com teores absorvidos por plantas de arroz e soja em materiais de solos contaminados. Foram estudadas sete amostras de solos com diferentes graus de contaminação empregando delineamento experimental inteiramente casualizado, com quatro repetições. Utilizando a técnica de ICP-OES, foram avaliados teores de Cu e Zn em folha diagnóstico e folha em final de ciclo (LCE) e no solo: teores disponíveis utilizando as soluções extratoras DTPA, Mehlich-1 e HCl, teores nas frações de solo solúvel+trocável, ligados à matéria orgânica e ligados a óxidos e o teor total. Para a soja e arroz, os teores de Cu e Zn extraídos do fracionamento correlacionaram significativamente com os teores obtidos na LCE. Para a soja, os teores de Zn extraídos com DTPA apresentaram alta correlação com os teores totais, enquanto que os teores de Cu extraídos pelos três extratores, DTPA, Mehlich-1 e HCl, correlacionaram com o teor total, provavelmente devido aos altos teores de Cu e Zn neste solo. Para o arroz, os teores de Cu e Zn extraídos pelas três soluções correlacionaram com teores em todas as frações e com o teor total.

A mudança no sistema de preparo do solo e cultivo das plantas, do sistema convencional para o plantio direto, na profundidade de amostragem e o aumento de rendimento das culturas, ao longo do tempo podem alterar os teores críticos de P, as faixas de fertilidade e as quantidades de fertilizante para as culturas. Este trabalho teve por objetivo calibrar os teores de P disponível, determinado pelos métodos Mehlich-1, Mehlich-3 e resina de troca iônica, nas culturas de soja, trigo e milho cultivadas no sistema plantio direto, e estimar as doses de P para a máxima eficiência econômica dessas culturas. Para isso, utilizaram-se amostras de solo e resultados de rendimento de grãos de experimentos em sistema plantio direto, com doses de P, realizados por instituições de ensino, pesquisa e extensão no Rio Grande do Sul. A partir da produção, determinaram-se a curva de calibração, as faixas de fertilidade e as doses de P para a máxima eficiência econômica. Os resultados indicam que o aumento médio no rendimento de grãos de milho, trigo e soja foi de 47,10, 12,37 e 7,20 kg ha-1 kg-1 de P2O5, respectivamente. Os coeficientes de determinação entre o rendimento relativo e os teores de P no solo aumentaram quando se agruparam os solos por classes texturais e foram maiores na camada de 0-10 cm em relação à de 0-20 cm; os teores críticos de P com o método de Mehlich-1 foram de 7,5, 15,0 e 21,0 mg kg-1 na camada de 0-20 cm de profundidade e de 16,0; 28,0 e 40,0 mg kg-1 na camada de 0-10 cm, nas classes texturais 1, 2 e 3, respectivamente. As faixas de fertilidade de P foram maiores nos métodos de Mehlich-3 e resina, se comparados ao método Mehlich-1. As doses do fertilizante fosfatado para as culturas de soja e milho foram maiores que as atualmente recomendadas para produção de 90 % do rendimento máximo. Verificou-se que os teores críticos de P são maiores em solos cultivados sob sistema plantio direto com soja, trigo e milho tanto na camada de 0-20 cm como na de 0-10 cm de profundidade e que os métodos da resina e Mehlich-3 apresentaram faixas de fertilidade mais amplas do que o método Mehlich-1.The change of cultivation systems from conventional to no-tillage, the change in soil sampling depth and the higher crop yields over time can influence the critical P content, fertility ranges and fertilizer doses recommended for crops. The objective of this work was to calibrate the soil P tests, Mehlich-1, Mehlich-3 and anion-exchange (AER) resin for soybean, wheat and corn plants cultivated under no-tillage system, and to estimate the P fertilizer amounts for a maximum economic yield. For this purpose soil samples and yield results from several experiments under no-till and different P doses, conducted by institutions of education, research and extension of the state of Rio Grande do Sul. The calibration curves were fitted using non-linear model functions, and the levels of soil fertility and fertilizer doses for a maximum economic yield were inferred. Results indicate that the average increases in corn, wheat and soybean yields were 47.1, 12.4 and 7.2 kg ha-1 kg-1 P2O5, respectively; the determination coefficients between the relative yield and soil P concentrations were higher when the soils were separated by texture classes and were highest in the 0-10 cm than the 0- 20 cm layer; the critical values of P, based on Mehlich-1 were 7.5; 15.0 and 21.0 mg kg-1the 0-20 cm layer, and of 16.0, 28.0 and 40.0 mg kg-1 in the 0-10 cm layer in the clay classes 1, 2 and 3, respectively; P fertility ranges were wider by Mehlich-3 and AER as compared to Mehlich-1; the quantities of P fertilizer were higher for soybean and corn when compared to the currently recommended quantities. The critical P concentrations are higher in soils under no-tillage with soybean, wheat and corn in the 0-20 as well as the 0-10 cm layer; the fertility ranges by resin and Mehlich-3 were wider than by Mehlich-1; the fertilizer P quantities are higher for soybean and corn grown under no-tillage.

No Brasil são cultivadas duas espécies de café: Coffea arabica L. e Coffea canephora Pierre. As pesquisas com adubação com Zn têm sido feitas, principalmente, com cultivares arábica. Esta pesquisa foi realizada com objetivo de obter a relação entre os teores de Zn disponível pelos extratores DTPA e Mehlich-1 em plantas de C. arabica cv. Mundo Novo IAC 379-19 (MN) e C. canephora cv. Apoatã IAC 2258 (AP), bem como em plantas enxertadas (MN/AP). Os tratamentos foram obtidos pelo fatorial 3 x 3, entre materiais genéticos (MN, AP e MN/AP) e doses de Zn (0, 10 e 20 mg dm-3). O teor de Zn na planta, em relação à disponibilidade do nutriente no solo, independentemente dos extratores, varia com a espécie e a combinação entre espécies e a enxertia. Os extratores DTPA e Mehlich-1 apresentaram eficiência semelhante para determinar o teor de Zn disponível no solo, independentemente da espécie (C. arabica e C. canephora). A absorção máxima de Zn ocorreu com teor disponível de 5,6 mg dm-3 (DTPA) e 6,6 mg dm-3 (Mehlich-1) para a cultivar Mundo Novo (C. arabica). Para a espécie C. canephora cv. Apoatã e nas plantas enxertadas (MN/AP), não foi estabelecida a máxima absorção de Zn, independentemente dos extratores, nas doses utilizadas no experimento.Two species of coffee (Coffea arabica L. and Coffea canephora Pierre) are cultivated in Brazil, but most research on Zn fertilization to date has focused on C. arabica. This study was carried out to determine the functional relationship between soil Zn availability determined by DTPA and Mehlich-1 extractors and Zn content in coffee plants belonging to the species C. arabica, cv. Mundo Novo IAC 379-19 (MN) and C. canephora, cv. Apoatã IAC 2258 (AP), as well as grafted plants (MN/AP). The treatments were a 3 x 3 factorial combination of cultivars (MN, AP and MN/AP) and Zn doses (0, 10 and 20 mg dm-3). The plant Zn content, in relation to soil Zn availability, does not depend on the extractant, but varies with the coffee species or grafted species combination. The DTPA and Mehlich-1 extractants were similarly efficient to quantify the soil Zn availability, independent of the coffee species (C. arabica and C. canephora). Zn uptake peaked at soil Zn contents of 5.6 mg dm-3 (DTPA) and 6.6 mg dm-3 (Mehlich-1) for Mundo Novo (C. arabica) cultivar. Based on the Zn doses employed in the present study, the maximum Zn uptake of C. canephora (cv. Apoatã) and grafted plants (MN/AP) could not be determined, independently of the soil extractants.

It is important to know the mechanisms for forage development, especially those related to the tolerance of potentially toxic elements, when considering their use in phytoremediation in heavy metal contaminated areas. In this study, we evaluated plant growth, concentration, and the availability of cadmium (Cd) for forage grasses (Panicum maximum Jacq. cv. Aruana and cv. Tanzânia; Brachiaria decumbens cv. Basilisk; Brachiaria brizantha cv. Xaraés and cv. Marandu) cultivated in Cd contaminated soils. The experiments were performed under greenhouse conditions over a 90-day evaluation period, and the Cd rates were 2, 4, and 12 mg/kg of soil. The relative growth rate of the forage grasses decreased as Cd rates increased, and the following descending order of susceptibility was observed: Marandu > Xaraés > Aruana > Tanzânia > Basilisk, with regard to phytotoxicity in these plants. The forage Cd concentration increased in line with increases in the Cd rates. Cd contents extracted by Mehlich-1 and by diethylenetriaminepentaacetic acid presented high positive correlation with forage relative growth. The forage plants did not block Cd entry into the food chain because they were not capable of limiting Cd absorption. [ABSTRACT FROM AUTHOR]

A avaliação do método modificado da resina de troca de íons para extração de Mn e Fe dos solos foi o objetivo desta pesquisa. Foram utilizadas 44 amostras de solo, cujos teores de Mn variaram de baixos a altos e de Fe de médios a altos. Como plantas-teste, utilizaram-se o milho e a soja, cultivadas em casa de vegetação. O Fe e o Mn do solo foram determinados, usando o método modificado da resina de troca de íons, DTPA, AB-DTPA, Mehlich-1 e Mehlich-3. Os coeficientes de correlação entre Mn no solo e Mn acumulado na parte aérea da soja foram: resina (0,62*), DTPA (0,58*), Mehlich-3 (0,54*), Mehlich-1 (0,51*) e AB-DTPA (0,26NS). Para o milho, houve correlação entre Mn-solo e Mn-planta somente nas amostras de solo com baixos teores desse elemento, para todos os extratores, exceto para AB-DTPA. Concluiu-se que a resina foi tão eficiente quanto os extratores DTPA, M-1 e M-3 em avaliar a disponibilidade de Mn para a soja, e que nenhum extrator foi eficiente em avaliar a disponibilidade de Fe para as plantas de milho e soja, com 53 dias de idade, cultivadas em casa de vegetação.The objective of this research was to evaluate a modified ion exchange resin method for Mn and Fe extraction from soils. Forty-four soil samples presenting low, medium, and high Mn and medium to high Fe concentrations were used. Maize and soybeans plants were grown as test plants in a pot experiment in a greenhouse. Soil samples were analyzed for Mn and Fe using the modified ion exchange resin, DTPA, AB-DTPA, Mehlich-1, and Mehlich-3 methods. The correlation coefficients between soil Mn and Mn accumulated in the soybean shoot were: ion exchange resin (0.62*), DTPA (0.57*), Mehlich-3 (0.54*), Mehlich-1 (0.51*), and AB-DTPA (0.26). For maize, significant correlation coefficients between soil Mn and plant-Mn were obtained only when low-initial Mn soil samples were considered for all extractants, except for AB-DTPA. For soybeans, the modified ion exchange resin method was as efficient as DTPA, Mehlich-1 and Mehlich-3 for the evaluation of soil Mn availability. None of the methods was efficient for evaluating the soil Fe availability for the 53 day-old maize and soybean plants grown in greenhouse.

A influência de características físicas e químicas relacionadas com o fator capacidade de P (FCP) na determinação dos níveis críticos de P pelos extratores Mehlich-1, Mehlich-3 e Bray-1 e na parte aérea de plantas foram estudadas em amostras superficiais de seis solos de Pernambuco cultivadas com Brachiaria brizantha (Hochst ex A. Rich.) Stapf. cv Marandu. O estudo foi realizado em casa de vegetação, com amostras de solos de diferentes teores de argila, nas quais foram aplicadas doses de P definidas pelos valores do P remanescente (P-rem). O experimento consistiu de um fatorial 6 x 6 (seis solos e seis doses de P), com os tratamentos distribuídos em blocos ao acaso, com três repetições. O teor de argila não foi tão estreitamente correlacionado com o FCP, com o nível crítico de P no solo, nem com os níveis críticos de P em B. brizantha. As características que melhor refletiram o FCP foram a capacidade máxima de adsorção de P (CMAP) e o P-rem. Como a CMAP é uma análise de difícil operacionalização, a determinação do P-rem é indicada para estimar o FCP do solo em laboratório de rotina. Dentre os extratores utilizados para quantificar o P disponível, o Bray-1 apresentou a maior recuperação do P aplicado e o Mehlich-1 a menor. Os extratores que melhor se correlacionaram com o P absorvido pelas plantas foram o Mehlich-1 e o Mehlich-3. Os valores dos níveis críticos nos solos variaram de 15,2 a 138,5 mg dm-3, no primeiro corte, e de 2,1 a 62,3 mg dm-3, no segundo corte. Características químicas como CMAP e P-rem influenciaram os níveis críticos de P nos solos e planta. Os níveis críticos de P no solo e em plantas de B. brizantha foram menores em solos com maior CMAP e com menor P-rem.

A determinação do fósforo potencialmente disponível por meio dos extratores químicos é dificultada em solos de carga variável, uma vez que existem diversos graus de energia de ligação com os colóides. O objetivo do presente trabalho foi avaliar o número mínimo de extrações sucessivas necessárias para estimar o fósforo potencialmente disponível, com os métodos de Mehlich-1 e Mehlich-3 e resina de troca aniônica (RTA). Foram realizadas treze extrações sucessivas com os três métodos em amostras de um Latossolo Vermelho distroférrico típico sob sistema plantio direto com doses crescentes de fósforo. Os resultados mostraram que uma única extração com Mehlich-1, Mehlich-3 ou RTA extrai apenas 29, 35 e 37 % do fósforo potencialmente disponível, respectivamente. Para obter o fator quantidade, foram necessárias sete extrações sucessivas com a RTA e quatro com os métodos Mehlich-1 e 3. O método da RTA foi mais eficiente no diagnóstico dos teores de fósforo nos tratamentos com baixa disponibilidade, enquanto os métodos Mehlich-1 e 3 foram mais eficazes naqueles com alta disponibilidade de fósforo.

Os fosfatos naturais reativos têm sido utilizados como fonte alternativa de fósforo (P) à cultura de arroz irrigado no estado do Rio Grande do Sul. O extrator Mehlich-1 é o método oficial de avaliação na disponibilidade de P em solos adubados com fonte solúveis, mas pode ser inadequado para solos adubados com fosfatos naturais, devido à possibilidade de dissolução excessiva das partículas de fosfatos naturais reativos por este extrator. Desenvolveu-se um experimento em casa de vegetação no Campus da PUC, RS, em Uruguaiana, no período de novembro a dezembro de 2009, com o objetivo de avaliar a disponibilidade de P em solos adubados com fosfato natural reativo, extraído pelo método da resina de troca aniônica (RTA), Mehlich-1 e Mehlich-3. Os solos foram previamente incubados com quatro doses de P (0; 9,82; 19,65 e 39,30 mg kg-1 de P) e cultivados com arroz irrigado durante 40 dias. Foram determinados os teores de P disponível extraído pelos diferentes extratores após o período de incubação. Durante o alagamento, foram analisados as concentrações de Fe, P e Ca e o pH na solução do solo. Após 40 dias de alagamento, foi avaliada a produção de matéria seca e a concentração de P na parte aérea das plantas. Os coeficientes de determinação (r2) obtidos entre P acumulado pelas plantas de arroz e o P extraído foram: 0,84 para a Resina de troca iônica (RTA); 0,58 para o Mehlich-1 e 0,61 para o Mehlich-3. Dentre os métodos testados, o método da RTA foi mais eficiente na extração de P do solo para avaliar a disponibilidade de P para a cultura de arroz irrigado em solos adubados com fosfatos naturais. A separação dos solos em grupos, segundo o material de origem e os teores de óxidos de ferro de baixa cristalinidade extraídos com oxalato a pH 6,0, resultou em melhor eficiência de todos os métodos testados para avaliar a disponibilidade de P para o arroz irrigado em solo adubado com fosfato natural reativo.

Procedimentos baseados em alterações nas propriedades químicas podem atuar como agentes mitigadores da fitotoxidez de metais pesados no solo. No entanto, é difícil predizer os efeitos de diferentes materiais sobre a disponibilidade de metais em solo contaminado simultaneamente por vários metais. O presente estudo, desenvolvido em solo proveniente de área de rejeitos de uma unidade de extração e industrialização de zinco da Companhia Mineira de Metais-CMM, em Três Marias (MG), objetivou avaliar os teores, a distribuição entre diferentes frações e a biodisponibilidade de Zn, Cd, Cu e Pb nesse solo, após incubação por seis meses com diferentes doses de carbonato, gesso, vermicomposto, serragem e Solomax. Após a incubação, retiraram-se amostras de cada tratamento para análises químicas de fracionamento de metais e extrações simples com DTPA e com Mehlich-1 e repicaram-se plântulas de Mimosa caesalpiniaefolia Benth. (sabiá) para o solo onde cresceram por 90 dias. Os tratamentos causaram alterações nas principais formas dos elementos no solo. Para o Zn, que apresenta os maiores teores nesse solo, houve efeito da aplicação de carbonato, que reduziu a fração trocável de 842 mg kg-1, no controle, para 32 mg kg-1. Houve também uma redução do Zn-trocável com a aplicação de Solomax. Os teores de Zn na parte aérea das plantas reduziram-se de 544,85 mg kg-1, no controle, para 32,20 mg kg-1 com a aplicação de carbonato. O Solomax reduziu em 87% o teor deste elemento nas plantas. Os demais materiais não exerceram efeitos consistentes sobre os teores dos metais na planta. A adição de materiais orgânicos aumentou o teor de Cu e de Pb na fração orgânica e residual, sem efeito na biodisponibilidade. O gesso aumentou a biodisponibilidade dos metais estudados, com exceção do Pb. Ao contrário do que foi verificado para os outros elementos, os teores de Cd na planta correlacionaram-se com as quantidades deste extraídas por DTPA (0,82**) e por Mehlich-1 (0,60**), e os de Zn com MgCl2 (0,49*) e DTPA (0,49*). As extrações seqüencial e simples, com DTPA e Mehlich-1, evidenciaram efeitos diferenciados dos materiais sobre os metais no solo. O Cd foi o elemento com melhor previsão de biodisponibilidade pelos extratores utilizados. O emprego de carbonato foi o tratamento mais eficaz em reduzir a disponibilidade dos metais para M. caesalpiniaefolia.

Soil phosphorus (P) availability was compared with Mehlich-1 soil testing and P fractionation at a research farm ( RF) and 32 private farms ( PFs) in north Florida. The environmental risks caused by P release were evaluated using the P saturation ratio ( PSR). Soil Mehlich-1 P at the RF and the PFs was 41.9 ± 4.1 and 278 ± 13 mg/kg, respectively. The dominant inorganic P fraction for all farms was Na OH-Pi (Al/Fe-bound P) followed by HCl-Pi (Ca/Mg-bound P) at most of the PFs but by Na OH-Po for the RF. Furthermore, the high PSR at the PFs indicated high risks of P loss from soil. To improve P use efficiency and enhance ecological sustainability, better P nutrient management should be implemented for Florida crop production. [ABSTRACT FROM AUTHOR]

Com o objetivo de avaliar a eficiência de três extratores de P em dois latossolos (LEa e LRa) do Mato Grosso do Sul, foi conduzido um experimento em casa de vegetação, com três fontes de P (superfosfato triplo, fosfatos naturais de Araxá e de Gafsa), em cinco doses (0, 50, 150, 450 e 600 mg P kg-1 de solo). Utilizou-se o feijoeiro como planta-teste. Os parâmetros produção de matéria seca, P acumulado na parte aérea, altura das plantas e número de folhas trifolioladas foram correlacionados com os teores de P extraídos pelos métodos de Mehlich-1, Mehlich-3 e resina trocadora de íons. Os métodos da resina e Mehlich-3 foram mais sensíveis às variações de solos. Quanto à eficiência, os extratores classificaram-se na seguinte ordem: resina > Mehlich-3 > Mehlich-1. O método da resina, independentemente do tipo de solo e da fonte de P utilizada, apresentou as melhores correlações com as características das plantas avaliadas, mostrando-se mais adequado em estimar o P disponível. Os teores de P extraídos entre Mehlich-3 e resina são altamente correlacionados entre si.With the objective of evaluating the efficiency of three phosphorus extractors in two Mato Grosso do Sul State oxisols, in Brazil, one greenhouse experiment was carried out with three P sources (triple superphosphate, Araxá rock phosphate and Gafsa rock phosphate), all in five levels (0, 50, 150, 450, and 600 mg per kg of soil). Common bean was used as test plant. In order to evaluate the phosphorus availability in the soils, the dry matter yield, the above ground phosphorus content, the plants height and the number of trifoliate leaves were correlated with the extracted phosphorus by Mehlich-1, Mehlich-3 and ion exchange resin methods. Mehlich-3 and resin were more sensitive to soil variations. According to their efficiencies, the extractors were classified in the following order: resin > Mehlich-3 > Mehlich-1. The resin method showed the best correlations with the plants characteristics, thus showing to be the most suitable in forecasting the available P in different soils and P sources. The best correlations were yielded by the resin and Mehlich-3 methods.

Com o objetivo de avaliar a disponibilidade de fósforo em amostras de solos representativos da Amazônia, desenvolveu-se um experimento em casa de vegetação do Centro de Energia Nuclear na Agricultura, Piracicaba (SP), de outubro de 1993 a março de 1994, utilizando-se amostras da camada superficial de cinco solos (LA-médio, LA-argiloso, LA-muito argiloso, PV-argiloso e PV-muito argiloso). Foram usados, como fontes de P, superfosfato triplo, termofosfato yoorin em pó, termofosfato yoorin semi-acabado e fosfato natural da Carolina do Norte, nas doses de P equivalentes a 0, 40, 80 e 120 mg kg-1 de solo. Caupi e arroz foram usados como plantas-testes, e os resultados de produção de matéria seca e de P acumulado na parte aérea foram correlacionados com os de teores de P nas amostras de cada solo. A extração de P foi efetuada por meio dos métodos da resina trocadora de ânions, Mehlich-1, Mehlich-3 e Bray-I. Os resultados obtidos demonstraram que o extrator Mehlich-1 extraiu grandes quantidades de fósforo nos tratamentos com fosfato natural da Carolina do Norte. Independentemente da fonte de fósforo utilizada, o extrator Mehlich-3 apresentou as melhores correlações com o caupi e o arroz. Os extratores Mehlich-3 e Bray-I apresentaram maior sensibilidade às variações de solo. O extrator Mehlich-3 mostrou-se adequado na avaliação da disponibilidade de fósforo para as plantas, em diferentes condições de solos e fontes de fósforo.

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In soil laboratory testing, the acid 1-amino-2- naphthol-4-sulfonic (ANS) is used as reducing agent to determine P by UV/Visible spectrometry. However, there are risks to laboratory technician healthy and an alternative is the use of ascorbic acid (AA). But, changes in the analytical protocol may induce variations in results, been necessary to standardize and calibrate. The objective of this study was to evaluate the ANS and AA in extracts of Mehlich-1 and 3 in ranges 15, 30, 45, 60 and 120min of reaction. There was no difference in P concentration determined by both reducers when compared within each extractor. Ascorbic acid can substitute the ANS solution for P determination and the suggested reaction interval for colorimetric quantification is between 30 and 60min for both substances. [ABSTRACT FROM AUTHOR]

When applied to agricultural soils, phosphate fertilizers and the mineral or organic compounds present in solid and/or liquid waste may raise phosphorus (P) content and increase soil P saturation. The degree of phosphorus saturation (DPS) is a good indicator of potential P loss from agricultural soils. The purpose of this study was to calculate the DPS of samples from an Oxisol amended for 5 years with biosolids and mineral fertilizer. DPS was calculated based on P, iron, and aluminum extracted by ammonium oxalate and oxalic acid (DPS) or by Mehlich-1 solution (DPS). Treatments included NPK mineral fertilization (175 kg ha of P), B1 = 19.02 t ha of biosolids (350 kg ha of P), B2 = 38.17 t ha of biosolids (703 kg ha of P), B3 = 76.26 t ha of biosolids (1,405 kg ha of P), and a control (no P added). Water-extractable P (WEP) was also measured. Critical levels of DPS and DPS (21 and 24 %, respectively) were only achieved in the topsoil (0-0.1 m) at the highest biosolid dose. Concentration of WEP was positively correlated to DPS and DPS. The DPS method may be an alternative to DPS for assessing the environmental risk of P loss from soil into surface runoff. [ABSTRACT FROM AUTHOR]

Conduziu-se um experimento com o objetivo de determinar a disponibilidade de P em solos cultivados com Brachiaria brizantha pelos extratores Mehlich-1, Mehlich-3 e Bray-1, e de correlacionar o P absorvido e acumulado pelas plantas com o P extraído. Utilizaram-se amostras superficiais, com diferentes teores de argila, às quais foram aplicadas doses de P definidas pelos valores do P remanescente. O experimento consistiu de um fatorial 6 solos e 6 doses de P, em blocos ao acaso, com 3 repetições. O extrator Bray-1 apresentou a maior recuperação do P aplicado, e o Mehlich-1, a menor. Os níveis críticos variaram de 15,03 a 138,52mg dm-3, no primeiro corte, e de 2,07 a 62,31mg dm-3, no segundo corte. Os extratores que melhor se correlacionaram com o P absorvido e acumulado pelas plantas foram o Mehlich-1 e o Mehlich-3.

This study compares the effect of lime additions on the spatial variability of Fe, Mn and Zn extracted by Mehlich-1 during three different growth stages from an acid paddy soil, a Typic Plintacualf, in Corrientes, Argentina. Field trials were set up involving three treatments: control, without lime addition, plus two different dolomite doses of 625 and 1250 kg ha. Soil was sampled first before sowing in aerobic conditions and then two more times in anaerobic conditions, i.e. by bunch formation and flowering. Ninety-six samples per plot were taken per lime treatment and sampling period, using a nested sampling strategy. Liming significantly increased extractable Fe and Mn, but decreased extractable Zn. The spatial variability of the studied soil properties was assessed using semivariogram analysis and examination of kriging maps. Models were fitted to experimental semivariograms for 27 data sets, i.e. three different soil properties, each of them sampled in three treatments and during three dates. Soil extractable and Fe, Mn and Zn exhibited a rather strong spatial dependence, as nugget variance was either null or a small proportion of the total variance, and this all over the three different study periods and for the three lime treatments. Geostatistical analysis provided insight into possible processes responsible of the observed spatial variability patterns within the rice soil. Kriging was useful in mapping soil micronutrient variability allowing identifying microrregions with high or low Fe, Mn and Zn concentrations, which showed the presence of small scale variability. These findings indicate the potential for applying the principles of precision agriculture to control spatiotemporal variability in rice fields. [ABSTRACT FROM AUTHOR]

Abstract: The spatial variability and temporal stability of Fe extracted by Mehlich-1 was investigated on an acid rice soil, a typic Plintacualf, under different lime doses and redox potential (Eh) conditions in Corrientes, Argentina. Soil was sampled firstly in aerobic conditions, before sowing and then twice more in anaerobic conditions, i.e. 4 and 8weeks after flooding. Three liming treatments were imposed: control (without any lime addition) and two dolomite doses (625 and 1250kgha−1). Ninety-six samples were taken for each sampling period and dolomite treatment. Flooding caused a decrease in Eh and an increase in pH. Increasing dolomite dose produced pH increase, while it enhanced Eh decrease, both in aerobic and in anaerobic conditions. Mehlich-1 extractable Fe was 4 to 12 times higher 8weeks after flooding than in aerobic conditions. Increasing dolomite amendment slightly decreased Mehlich-1 extractable Fe in aerobic conditions, but sharply increased it in anaerobic conditions. Soil extractable Fe exhibited a rather strong spatial dependence over the three different study periods and for the three lime treatments, which was modelled by exponential and spherical models with low to moderate nugget effect. Kriging was useful in mapping variability of Mehlich-1 Fe, allowing description of microrregions with contrasting concentrations. Semivariogram parameters and kriging maps also showed a lack of temporal stability in the patterns of spatial dependence of extractable Fe for all the studied dolomite treatments. [Copyright &y& Elsevier]

Eucalyptus is the most widely planted forest species in Brazil (∼3.4 million hectares). Ongoing rotations and high yields lead to the occurrence of copper (Cu), manganese (Mn), iron (Fe), and zinc (Zn) deficiency symptoms. The objectives of this work were to identify the most appropriate extractant for evaluating micronutrient availability in commercial Eucalyptus plantations and to evaluate the influence of soil properties on Eucalyptus foliar micronutrient contents. Soil micronutrient contents were extracted by Mehlich 1, Mehlich 3, and diethylenetriaminepentaacetic acid (DTPA). Mehlich 1 and Mehlich 3 extracted the greatest amounts for all micronutrients analyzed. Foliar Cu, Mn, and Zn contents showed significant and positive relationships with soil Cu, Mn, and Zn contents extracted by the three solutions. Soil organic carbon (SOC), soil clay content, and soil pH improved significantly the power of regression models in estimating foliar micronutrient contents. The improvement was greater for Mehlich 3 and DTPA extractants than for Mehlich 1. [ABSTRACT FROM AUTHOR]

Copper (Cu) and zinc (Zn) amounts extracted with 0.1molar L-1 HCl (HCl) for the most representative soil types of Rio Grande do Sul State (Brazil) were compared with those extracted with Mehlich-1 (M3) and Mehlich-3 (M3) solutions. The nutrients' amounts extracted by different methods indicated high correlation degree. The M3 solution extracted similar copper amounts than HCl; however, lower amounts of Zn. The M1 and M3 solutions are efficient for simultaneous multielement extraction and can be used in soil testing laboratories for RS and SC states. [ABSTRACT FROM AUTHOR]

A cotton ( Gossypium hirsutum )–peanut ( Arachis hypogaea L.) rotation is widely practiced in the southern coastal plain following the reemergence of cotton as a major crop in the 1990s. Very few plant nutrition studies have been conducted in the coastal plain (CP) with modern cotton varieties and none with the cotton–peanut rotation. Experiments with varying rates of nitrogen (N), phosphorus (P), and potassium (K) were conducted to determine if the recommendations from soil tests provide adequate nutrition for maximizing profit when yield goals are Georgia state averages, due to other conditions. From 1996 through 1998, N, P, and K experiments were conducted in cotton crops, and P and K experiments were conducted in peanut crops on Tifton loamy sand. Initial Mehlich‐1 P was 2 to 3 mg/kg (“low”) and Mehlich‐1 K was 50 to 64 mg/kg (“medium” for cotton and “high” for peanut). Each crop was grown each year. State average yields of cotton and peanuts were produced. There was no response in cotton yield to N rates from 34 to 136 kg N/ha. Lack of response may have been due to the fact that the field had not been in production for several years prior to 1996 and there was ample soil mineral N. In 1997 and 1998, residual N provided by N fixation by the previous peanut crop appeared to be sufficient. Maximum profit from P fertilization in cotton was attained at 50 kg P/ha, the recommendation from the soil test. However, a University of Georgia Cooperative Extension Service recommendation to double the P rate for new land with a “low” Mehlich‐1 P soil test was not validated. Cotton yield did not respond to K fertilization even though an application of 55 kg K/ha/year was recommended from the soil test. Peanut yield and grade did not respond to either P or K fertilization. The recommendation from the soil test was 40 kg P/ha/year and no K. Estimates of P removal were 11 kg/ha for cotton and 8 mg/ha for peanut crops. Estimates of K removal were 25 kg/ha for cotton and 22 kg/ha for peanut crops. Over 3 years, soil P was not depleted, but soil K was depleted. Approximately 12 kg P/ha were required to raise soil test P 1 mg/kg and 18 kg K/ha were required to raise soil test K 1 mg/kg (49 lb. P 2 O 5 to increase the P test 1 lb./acre, 38 lb. K 2 O to raise the K test 1 lb./acre). Additional studies are needed, but the current studies suggest that revisions in recommendations are needed for both cotton and peanut crops. [ABSTRACT FROM AUTHOR]