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The study was designed to quantify the contents of Pi fractions and correlate them with the P capacity factor of soils in the Brazilian semiarid region. We also evaluated the effect of soil P doses contact time and P availability for maize plants in alkaline soils of the Brazilian semiarid region. Soil samples were collected between the Piranhas-Açu (RN) and Jaguaribe (CE) rivers valleys. The maximum phosphate sorption capacity was highly correlated with the values of remaining P, indicating that it can be used as a measure to estimate the P capacity factor of these soils. Maximum P sorption capacity correlated with Fe2O3 and Ca2+ contents and pH values. These results demonstrate that P sorption is explained by P adsorption on the surface of iron oxides and by its precipitation with Ca2+ in alkaline soils. The contact time increases promote plant P contents decreased substantially in the first 30 to 60 days after fertilization and decreased until 120 days of incubation but then tended to stabilize at the longest soil P contact times. The clay content and P-remnant estimate the P capacity factor in alkaline soils. In alkaline soils, there is a predominance of P–Ca and P–Fe. The availability of P stabilizes after 120 days. The largest corn biomass occurs between the P doses of 256–288 mg dm−3. [ABSTRACT FROM AUTHOR]

Cultivating naturally colored fiber cotton has excellent potential for the Northeast of Brazil. However, its cultivation in the semiarid occurs with low use of technology and inputs in soils with the low phosphorus content. This work evaluated the productivity and fiber quality of naturally colored cotton cultivars under phosphorus fertilization in the Brazilian semiarid region. The experimental design was randomized blocks, with treatments arranged in split plots and four replications. The five P doses were allocated in the main plot, and four cotton cultivars were in the subplots. Variance analyses were performed for the characteristics evaluated in each agricultural harvest. Tukey test was used to compare the averages for cultivars and agricultural harvests. Increased P availability increased productivity and fiber quality of naturally colored cotton cultivars. Maximum fiber yield was obtained at 240; 240; 199.11, and 60 kg ha−1 in the first crop, respectively. The maximum fiber length was reached at 80.86 kg ha−1 in the BRS Verde cultivar. The maximum uniformity was obtained with the 138.49 kg ha−1, and the cultivar BRS Topázio obtained greater uniformity. Fiber strength increased with the application of P2O5. [ABSTRACT FROM AUTHOR]

In soils with adequate levels of fertility, it is possible to manage phosphate fertilization aiming at the grain production system, instead of each isolated crop. The objective was to evaluate the effects of the management of phosphate fertilization, place and time, on the soil and leaf P content, and crop yield in grain production systems. An experiment was conducted at the farm level in the municipality of Nazareno, state of Minas Gerais, Brazil, for four years on soil with adequate level of fertility. The treatments consisted of the management of phosphate fertilization by broadcast or furrow and dose for each crop or for the production system (spring/summer and autumn/winter crops), being: Control = without phosphate fertilization; Conventional = phosphate fertilization in the furrow in each crop; BTP = phosphate fertilization of the grain production system to broadcast; TPS = phosphate fertilization of the grain production system in the furrow of the spring/summer crop; TPW = phosphate fertilization of the grain production system in the furrow of the autumn/winter crop. Soil P content was evaluated in the third year of implantation, and the crops yield every season crop (maize, soybean, common bean and wheat). The P content in the leaves of maize and soybeans were evaluated in the spring/summer crops. The application of the total dose of phosphate fertilization for both crops in the sowing furrow of the spring/summer or autumn/winter crops (TPS and TPW) promoted operational advantages and increased soil P content in the 0-0.20 m layer, without reducing the yield of the spring/summer crops. Leaf P content was not affected. The Conventional management (phosphate fertilization in the furrow in each crop) provide greater yield of common beans and wheat during autumn/winter crops, which are more subject to water restriction due to less rainfall, even without increasing the soil P content. [ABSTRACT FROM AUTHOR]

No-tillage (NT) and no-tillage systems (NTS) are widely used conservation agriculture practices in Brazil, and in the state of Paraná, nearly 80% of annual crops are cultivated using these methods. Compared with NT, NTS sites permanently include: minimum soil disturbance, soil cover (straw and living vegetation) and crop rotation and diversification with cover crops. These practices often increase earthworm populations, that can be used to indicate soil health. Herein, we review soil health classification of NT sites, and the species found in Paraná state. We compiled information from 130 sites with NT or NTS, located in 29 counties, of which 93 had biomass and 91 had species richness data, aiming to compare NT with NTS sites, and the effect of the age of these practices on earthworm populations. Overall, 29 earthworm species were recorded, of which 17 were native, including many new to science. Mean abundance and biomass in NT + NTS were 104 ind m−2 and 2.5 g m−2, respectively, and richness 2.5 species per site. Abundance was significantly higher in NT than NTS in the initial phase of adoption, and both abundance and biomass decreased with increasing age of NT. Earthworm abundance and species richness were positively correlated with clayey soils and phosphorus content, while higher biomass was associated with soil carbon content and pH. A new classification system was proposed, with the categories poor (<50 ind. m−2, 1 species), moderate (≥50 to <100 ind m−2, 2 species), good (≥100 to <150 ind m−2, 3 species), very good (≥150 to 200 ind m−2, 4 species) and excellent (≥200 ind m−2, ≥5 species) soil health, using earthworm abundance and species richness, respectively. Most of the sites sampled showed poor or moderate soil health, with few displaying very good or excellent health, indicating the need for improved management practices, in order to promote earthworm populations and their potential benefits to soil fertility and plant production. • Overall 29 earthworm species (17 native) were found in no-tillage in Paraná state. • Abundance and biomass decreased with increasing no-tillage age. • Sites under no-tillage system in the consolidation phase, had higher earthworm abundance. • Farmers can classify their soil's health using earthworm abundance and species richness. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is one of the most important elements used in fertilizing soils in tropical regions due to the low efficiency of phosphate fertilization. This work aimed to fractionate inorganic P (Pi) in tropical soils of different mineralogical compositions and to relate these fractions with their respective phosphate buffer capacity (PBC) indicators. The soils were characterized physically, chemically and mineralogically. Additionally, we evaluated the P concentration that remained in solution of soil after equilibrium was met; this was termed P remaining (P-rem). In general, the Pi fractions of soils did not correlate with the PBC indicators. The P-H2O fraction showed a negative correlation with the P-Al fraction. Ferric minerals did not influence P fixation. P-rem showed a strong correlation with the maximum P adsorption capacity, adsorption energy, and the amorphous and crystalline forms of Fe. The minerals of aluminum contributed the most to P fixation. P-rem was the best estimator of PBC. The soils with high, moderate and low rates of P fixation showed high amounts of the fractions P-Al, P-Ca, and P-Fe, respectively. The results showed that P fixation was influenced by the fractions of P in the soil, suggesting that the efficiency of phosphate fertilizers in tropical soils depends on the mineralogy of the clay fraction within those soils. [ABSTRACT FROM AUTHOR]

Onion is an important vegetable crop, predominantly grown under conventional tillage system management. Alternatively, the vegetable no-tillage system uses cover crops to form a residue layer, which improves soil physical, chemical, and biological attributes. Aiming to understand the interaction of mycorrhizal and non-mycorrhizal cover crops, phosphatase activity, and soil phosphorus availability and uptake by plants, a no-tillage vegetable production system experiment with onion was carried out in Ituporanga, Southern Brazil. The treatments were black oats (Avena strigosa); rye (Secale cereale); oilseed radish (Raphanus sativus); rye + oilseed radish; black oats + oilseed radish, and a control with spontaneous plants. Additionally, two plots, a conventional tillage system area and a forest, both adjacent to the experiment, were evaluated. We measured cover crop biomass, onion yield, acid phosphatase activity, and resin-extracted phosphorus in the soil, shoot and root phosphorus content, and root colonization in cover crops, spontaneous plants, and onions. The treatments with cover crops had the highest plant biomass in winter and onion yield. Available soil phosphorus and acid phosphatase activity were higher in no-tillage plots than in the conventional tillage system area. The presence of non-mycorrhizal oilseed radish was associated with decreased colonization of rye and onion roots by arbuscular mycorrhizal fungi. No-tillage areas with cover crops or spontaneous plants in winter accumulated more phosphorus than conventional tillage system areas. The conventional tillage system showed adverse effects on most soil attributes, as shown by a Principal Component Analysis. [ABSTRACT FROM AUTHOR]

The anthropization of terrestrial environments has increased the production and concentration of nutrients and organic compounds in shallow bodies of water and in the soil along river banks, thereby causing changes in both water and soil quality. To examine the impact of anthropization on river environments, the phosphorus, potassium, and carbon content in the water and the phosphorus, potassium, and organic matter in the soil were analyzed at eighteen sites. The experimental area is located in an urbanized drainage basin located in the municipality of Lages, Santa Catarina (southern Brazil). The water samples were collected in two field surveys. The first one occurred between August and December 2016, and the second took place from March to June 2017. The soil samples were collected in one field survey from August 2016 and June 2017. The 18 sites were regularly distributed across forests, native grasslands, and urban areas. The dissolved phosphorus and potassium in the water were obtained by applying the methodology proposed by MURPHY & RILEY (1962), whereas the dissolved carbon in the water was mineralized by combustion using an oven at 800 ºC and calculated with the Analytik Jena Multi N/C 2100 TOC/TN Analyzer. On the other hand, the extractable phosphorus and potassium from the soil and organic matter were determined with the methodology described by TEDESCO et al. (1995). The results demonstrated that the concentration of dissolved phosphorus, potassium, and carbon in the water was greater in the parts of the river that cross through urban areas than in the parts of the river that course through grasslands and forests throughout practically the entire year. The same trend was observed with the phosphorus and potassium content in the soil along the river banks. However, the organic matter content in the soil was lower in the sections located in urban areas. The findings indicate that in urban areas where sewage treatment is either nonexistent or deficient, the release of domestic wastewater containing household detergents and soaps contributes to the increase in the content of phosphorus, potassium, and carbon in the water and phosphorus and potassium in the soil. [ABSTRACT FROM AUTHOR]

Successive applications of swine manure (SM) in agriculture may contribute to environmental contamination by excess of phosphorus (P). In this study, we analyzed the dynamics of P fractions in soil cultivated with Ilex paraguariensis, following successive applications of SM over a long period (> 40 years) in southern Brazil. Soil samples in the 0–5, 5–10 and 20–40 cm layers were collected in areas subjected to 35 (A35) and 45 (A45) years of SM application and an area with no anthropogenic intervention (M). The content of organic and inorganic P in the soil samples was quantified by sequential extraction with NaHCO3 0.5 mol L−1 (labile), H2SO4 (moderately labile), and NaOH 0.5 mol L−1 (recalcitrant). The potential of P adsorption was assessed using the solution of KH2PO4 which remained in contact with the soil for a night. Data were compared by Tukey test at 5% probability. The results showed that 35 and 45 years of successive SM application did not increase total P content in soil. In contrast, an increase in inorganic form of P was observed. In comparison to the forest area, SM application for 45 years increased the content of the labile inorganic P fraction by 168%, 162% and 290% in the 0–5, 5–10 and 20–40 cm soil layers, respectively. The accumulation of this fraction promoted the reduction of P adsorption in soil by 99%, 180% and 175% in the 0–5, 5–10 and 20–40 cm soil layers, respectively, increasing the risk of contamination of groundwater by P excess. [ABSTRACT FROM AUTHOR]

Large reserves of phosphorus (P) in Brazilian soils can be potentially used by crops. However, it is not well known how different tillage systems and past P fertilizer management strategies affect legacy P utilization. A trial was conducted in an Oxisol (Rhodic Haplustox) at Embrapa Cerrados, Federal District, Brazil to investigate the effects of different soil residual P conditions on maize yield. For 17 yr, annual summer crops were fertilized with 80 kg ha-1 yr-1 P2O5 in a split-plot design consisting of eight treatments: no-tillage system (NT) or conventional tillage (CT), fertilized with triple superphosphate (TSP) or reactive rock phosphate (RRP), applied to the crop furrow or broadcast. P fertilization was then discontinued and maize grown for 4 seasons relied on the residual soil P under NT or CT. Residual P use efficiency, calculated as a ratio between grain yield and total residual P in the soil, was greater under NT than CT, as a consequence of higher availability of P determined by Bray-1, Mehlich-1 and Olsen methods. Past use of RRP sustained better yields and higher residual P use efficiency, especially in NT, due to its lower solubilizing rate. P placement strategy did not change residual P use efficiency. We recommend assess amount of available P to identify sites in which residual P may sustain crop needs. Finally, the use of RRP, especially under NT, is a recommended management strategy for reducing phosphate fertilizer demand in heavily weathered soils of Central Brazil. [ABSTRACT FROM AUTHOR]

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Abstract In areas with extensive soil erosion, there is a need to identify the sources supplying sediment to rivers in order to improve our understanding of erosion processes and to guide the implementation of effective soil management measures. Geochemical elements are often used as tracers in sediment fingerprinting studies. Among them, P has often been used as it may specifically trace sediment originating from cropland. Although P-fractions can provide more detailed information than the total P content, their potential to distinguish between different potential sources of sediments has rarely been tested. The objective of the current research was to evaluate the contribution of sediment sources in a rural catchment (Arvorezinha, 1.23 km2) of Southern Brazil, using different sets of tracers (i.e. P-fractions only, geochemical tracers only, and a combination of both tracers). Three potential sediment source types were identified in the catchment: (i) cropland, (ii) unpaved roads and (iii) stream channel banks. Thirty-one suspended sediment samples were collected in the river draining this catchment during 9 significant floods between 2009 and 2011. Estimates of P-fractions were obtained by Hedley fractionation using anion exchange resin membrane (P resin); 0.5 mol L−1 NaHCO 3 (pH 8.5) (P bic); 0.1 mol L−1 NaOH (P NaOH0.1); 1.0 mol L−1 HCl (P HCl); 0.5 mol L−1 NaOH (P NaOH0.5); and residual P (P residual). Total organic (P org) and inorganic P (P inorg) were obtained by the ignition method. The concentrations of P HCl , P NaOH0.5 and P inorg in suspended sediments were higher than those found in the sources. Accordingly, these fractions were considered not to be conservative and were excluded from further analysis. With the exception of P residual , all P-fractions passed the Kruskal-Wallis H -test and were considered as potential tracers of sediment sources. When the P-fractions were combined with geochemical tracers, the discrimination power was much higher than when using geochemical tracers only. The Mahalanobis distance was 9% higher than that observed in the geochemical approach. The calculated contribution of sediment sources using the three approaches was very similar, and cropland was the dominant source of sediment, with calculated contributions of 56 ± 19, 46 ± 16 and 48 ± 16% for those approaches based on geochemical elements, P-fractions, and geochemical + P-fractions, respectively. These results demonstrate the effectiveness of some P-fractions to trace potential sediment sources in rural catchments, as they have a high discriminant power while remaining conservative during sediment transport in the catchment. Graphical abstract Unlabelled Image Highlights • Combining P-fractions with geochemical tracers increased the discrimination power. • P-fractions alone provided results similar to those obtained with geochemical tracers. • Three P-fractions in suspended sediments were considered non-conservative. • All P-fractions were considered as potential tracers of sediment, except residual P. [ABSTRACT FROM AUTHOR]

Strongly weathered soils (such as Oxisols), are inherently phosphorus (P) limiting and highly P-sorptive thus requiring continued P inputs for productive agriculture. Constant P inputs result in accumulation of soil P with increasing risk of eutrophication of waterways. The state of Santa Catarina is the largest pork producer in Brazil. Production is concentrated in confined systems, with large generation of nutrient rich waste, commonly utilised as fertiliser. The objective of this work was to investigate and quantify the impact of long-term P inputs in pig slurry to a high P-sorbing Oxisol under cropping in southern Brazil. Fifteen years of pig-slurry addition resulted in P accumulation and vertical movement down the soil profile in proportion to application rates, but significant effects were confined to the 0–20 cm soil layer. Phosphorus accumulated mainly in inorganic forms. Slurry input rates of 25, 50, 100, and 200 m 3  ha −1  y −1 resulted in accumulations of 25, 57, 106, and 159 kg P ha −1  y −1 (0–40 cm), of which only 8, 10, 23, and 28 kg P ha −1  y −1 were organic P forms. Mass balance showed that between 62 and 94% of the P inputs in slurry were accounted for in grain exports (7–35%), soil storage (58–83%), minimal amounts were estimated in crop residues (<1%), while the remainder (6–38%) was presumed to have been lost in drainage by overland flow. [ABSTRACT FROM AUTHOR]

Soil phosphorus (P) availability commonly limits the productivity of tropical croplands. While large fertilizer inputs can alleviate P limitation, this strategy is costly and relies on finite phosphate rock resources subject to price volatility. Nevertheless, high-P-input agriculture on P-poor and P-fixing soils is spreading rapidly in some regions of the tropics, particularly in Brazil, where farmers on average add twice as much P to soils as they harvest to ensure high yields. Here we ask whether P fertilizer inputs to tropical soils in excess of harvested P outputs will eventually build up a residual pool of soil P that crops can tap into if fertilizer inputs are decreased – a phenomenon observed in the U.S. and Western Europe, albeit on very different soils. We pose this question in Mato Grosso, Brazil, where we quantified soil P input-output budgets, total P, Bray-extractable P, P sorption capacity, P saturation, and other characteristics from a chronosequence of 31 plots that had been in soybean production for 0–31 years. Farmer interviews revealed ongoing annual additions of P fertilizer greater than P removals in crops, with an average farm P balance in the most recent year, including soybeans and a second harvest, of +14 kg P ha −1 y −1 . Soil total P and Bray-P 1 have increased, and P sorption capacity has decreased, with time in production. However, clayey soils rich in iron- and aluminum-oxides still have high P sorption capacity and low P saturation, even after three decades of intensive fertilization and residual P build-up. Our findings suggest that commodity crop producers farming on this soil type in Mato Grosso and other tropical regions may need to add annual inorganic P fertilizer inputs greater than the quantity of P recovered in harvests for up to a century or more before soil P budgets can be balanced without endangering yields. This result has implications for the sustainability of agricultural intensification in the tropics. [ABSTRACT FROM AUTHOR]

Phosphorus (P) retention capacity of soils directly affects the management of phosphate fertilization, and has economic and environmental importance. Brazil has expressive agricultural production and high edaphoclimatic variability; still, the detailed spatial distribution of P retention capacity is not known. Thus, machine learning models were created to estimate the P retention capacity of soils at superficial horizons using the variables: clay content, sand content, soil organic matter, pH, base saturation. The four best models were combined to create an ensemble (a combination of models), which was applied in a dataset (5524 samples) that comprises a sample data from the entire Brazilian territory. The ensemble was used to build a map of P retention capacity. Most of the country presented soils with medium P retention (40–60%), and large areas with very high retention capacity were found in the south of Brazil, a subtropical region mostly associated with clayey soils. High P retention was observed for Histosols, probably related to humic-Al(Fe) complexes. Nitisol, Ferralsol, Gleysol and Cambisol classes presented high P retention, especially for clayey soils with qualifiers related to bases/weathering (Dystric) and organic matter (Umbric and Humic). The correlation between Fe oxide minerals and P retention varied with soil color and drainage conditions mainly associated to redoximorphic reactions; the same was not observed for Al oxide minerals. This pioneer study revealed the distribution of P retention capacity across different soil classes in Brazil, which can help to define land use suitability and soil P management strategies that ensure profitable agricultural exploration. [Display omitted] • In 34% of the country, soils had P retention capacity framed as Low and 22% as High. • The Histosol class presenting soils with elevated P retention capacity (>60%). • For mineral soils, the highlighted classes were Nitisol, Ferralsol, Gleysol and Cambisol. • Soil color and drainage conditions had little effect on soil P retention capacity. [ABSTRACT FROM AUTHOR]

Soil phosphorus (P) utilization may be affected by agricultural complexity, in particular when combining annual crops and livestock grazing on the same land area and at overlapping times. Our objectives were to qualify and quantify soil organic and inorganic P compounds using sodium hydroxide-ethylenediaminetetraacetic acid (NaOH-EDTA) extraction and 31 P nuclear magnetic resonance spectroscopy ( 31 P NMR) in response to increasing complexity with integrated crop-livestock systems (ICLS) in subtropical Brazil. Soil at a depth of 0–5 cm was collected from three long-term (7 to 12 years) cropping studies with and without ruminant grazing of cover crops. All sites were managed under no tillage, and treatments with livestock were managed with moderate grazing intensity. In these agro-ecosystems, grazing compared with no-grazing had greater soil P content as total and bioavailable orthophosphate and lower soil organic P and fewer monoesters, including inositol phosphates. Grazing increased P bioavailability and reduced recalcitrant organic P concentration in soil; therefore, cropping systems that integrate livestock (ICLS) can be a sustainable alternative to improve P use in farming systems of subtropical Brazil. [ABSTRACT FROM AUTHOR]

Without proper management, land-use change (LUC) associated with producing sugarcane ( Saccharum officinarum ) for bioenergy in Brazil can lead to soil degradation and have negative implications on ecosystem functions. Phosphorus (P) depletion is one of the most frequent causes of land degradation in tropical environments, and as such, soil P pools have been identified as potential indicators of negative environmental impacts. We quantified soil P dynamics for the most common LUC sequence in sugarcane expansion areas [i.e., native vegetation (NV) to pasture (PA) to sugarcane (SC)], to determine if and how these changes could be used to evaluate environmental impacts of LUC in weathered Brazilian soils. Soil samples were collected from three areas in central-southern Brazil, representing the primary sugarcane-producing region of the world. Soil P fractionation was performed, and P stocks were calculated for the surface 30 cm. Soil chemical attributes and macrofauna data were correlated with P pools. Long-term conversions from natural ecosystems (Cerrado and Atlantic forest biome) to extensive PA decreased total P stocks by 31.2% indicating progressive soil degradation in these areas. In contrast, the LUC from PA to SC increased total P stocks by 35.6%; nevertheless, fertilization management altered the soil P-cycle, causing P accumulation in less plant-available forms. Available P increases to support adequate SC growth are still needed. Applying P using organic residues increased labile organic P and may be a complementary strategy for increasing nutrient supplies in SC fields. Phosphorus availability showed significant positive correlations with other soil chemical properties and clay content, while the functional diversity of soil macrofauna was strongly correlated with labile and biological P. We conclude that P pools can be useful indicators for assessing LUC modifications on soil quality in the tropics, and recommend they be used to assess land degradation and environmental sustainability within SC expansion areas in Brazil. [ABSTRACT FROM AUTHOR]

Crop production in the Brazilian Cerrado is limited by soil phosphorus (P) supply without large inputs of inorganic P fertilizer, which may become more costly and scarce in the future. Reducing dependency on fertilizer P requires a greater understanding of soil P supply in the highly weathered soils in this important agricultural region. We investigated the impact of no tillage (NT) and conventional tillage (CT) agriculture on accumulated (legacy) soil P and P forms in four long-term sites. Compared to the native savanna soils, tilled soils receiving regular annual P fertilizer inputs (30–50 kg P ha − 1 ) increased all forms of inorganic and organic P, except highly recalcitrant P associated with the background lithology. However, 70–85% of the net added P was bound in moderately labile and non-labile forms associated with Fe/Al oxyhydroxides rather than in plant available forms. Under NT agriculture, organic P forms and labile and non-labile inorganic P forms were all significantly (P < 0.05) increased in the surface soil, except for one site with maize residues where labile inorganic P was increased more under CT agriculture. The contribution of organic P cycling in these tropical soils increased after conversion to agriculture and was proportionally greater under NT. The results highlight the large amounts of unutilized legacy P present in Brazil's Cerrado soils that could be better exploited to reduce dependency on imports of finite phosphate rock. No tillage agriculture confers a positive albeit relatively small benefit for soil P availability and overall soil function. [ABSTRACT FROM AUTHOR]

In this paper, soil carbon, nitrogen and phosphorus concentrations and stocks were investigated in agricultural and natural areas in 17 plot-level paired sites and in a regional survey encompassing more than 100 pasture soils In the paired sites, elemental soil concentrations and stocks were determined in native vegetation (forests and savannas), pastures and crop-livestock systems (CPSs). Nutrient stocks were calculated for the soil depth intervals 0-10, 0-30, and 0-60 cm for the paired sites and 0-10, and 0-30 cm for the pasture regional survey by sum stocks obtained in each sampling intervals (0-5, 5-10, 10-20, 20-30, 30-40, 40-60 cm). Overall, there were significant differences in soil element concentrations and ratios between different land uses, especially in the surface soil layers. Carbon and nitrogen contents were lower, while phosphorus contents were higher in the pasture and CPS soils than in native vegetation soils. Additionally, soil stoichiometry has changed with changes in land use. The soil C :N ratio was lower in the native vegetation than in the pasture and CPS soils, and the carbon and nitrogen to available phosphorus ratio (PME/ decreased from the native vegetation to the pasture to the CPS soils. In the plotlevel paired sites, the soil nitrogen stocks were lower in all depth intervals in pasture and in the CPS soils when compared with the native vegetation soils. On the other hand, the soil phosphorus stocks were higher in all depth intervals in agricultural soils when compared with the native vegetation soils. For the regional pasture survey, soil nitrogen and phosphorus stocks were lower in all soil intervals in pasture soils than in native vegetation soils. The nitrogen loss with cultivation observed here is in line with other studies and it seems to be a combination of decreasing organic matter inputs, in cases where crops replaced native forests, with an increase in soil organic matter decomposition that leads to a decrease in the long run. The main cause of the increase in soil phosphorus stocks in the CPS and pastures of the plot-level paired site seems to be linked to phosphorus fertilization by mineral and organics fertilizers. The findings of this paper illustrate that land-use changes that are currently common in Brazil alter soil concentrations, stocks and elemental ratios of carbon, nitrogen and phosphorus. These changes could have an impact on the subsequent vegetation, decreasing soil carbon and increasing nitrogen limitation but alleviating soil phosphorus deficiency. [ABSTRACT FROM AUTHOR]

Historical data of land use change (LUC) indicated that the sugarcane expansion has mainly displaced pasture areas in Central–Southern Brazil, globally the largest producer, and that those pastures were prior established over native forests in the Cerrado biome. We sampled 3 chronosequences of land use comprising native vegetation (NV), pasture (PA), and sugarcane crop (SC) in the sugarcane expansion region to assess the effects of LUC on soil carbon, nitrogen, and labile phosphorus pools. Thirty years after conversion of NV to PA, we found significant losses of original soil organic matter (SOM) from NV, while insufficient new organic matter was introduced from tropical grasses into soil to offset the losses, reflecting in a net C emission of 0.4 Mg ha − 1 yr − 1 . These findings added to decreases in 15 N signal indicated that labile portions of SOM are preserved under PA. Afterwards, in the firsts five years after LUC from PA to SC, sparse variations were found in SOM levels. After more than 20 years of sugarcane crop, however, there were losses of 40 and 35% of C and N stocks, respectively, resulting in a rate of C emission of 1.3 Mg ha − 1 yr − 1 totally caused by the respiration of SOM from C4-cycle plants. In addition, conversion of pastures to sugarcane mostly increased 15 N signal, indicating an accumulation of more recalcitrant SOM under sugarcane. The microbe- and plant-available P showed site-specific responses to LUC as a function of different P-input managements, with the biological pool mostly accounting for more than 50% of the labile P in both anthropic land uses. With the projections of 6.4 Mha of land required by 2021 for sugarcane expansion in Brazil to achieve ethanol's demand, this explanatory approach to the responses of SOM to LUC will contribute for an accurate assessment of the CO 2 balance of sugarcane ethanol. [ABSTRACT FROM AUTHOR]

Studies of responses of native and introduced grassland species to lime and phosphorus ( P) applications could contribute to improved understanding of the potential production of South American natural grasslands. To determine the effect of applying lime and different P sources on forage production, diversity and floristic composition, and on soil chemical properties, a small-plot experiment was conducted over 12 years in natural grassland oversown with Lolium multiflorum and Trifolium vesiculosum in the Campos of southern Brazil. In treatments with soluble phosphate application, dry-matter ( DM) yield in November 2008, after 164 d of winter and early spring growth, increased from 2·3 to 3·2 t ha−1. Differences in DM yield in March 2009, after 111 d of growth during late spring and early summer, were not significant. The DM yield in April 2010, after 419 d of growth, increased from 7·7 to 9·2 t ha−1 in the treatments with P, regardless of the P source. Increased forage yield during the slow growth period in winter was only possible with the introduction of winter-growing species ( L. multiflorum and T. vesiculosum) and soluble phosphate application. Assessment of annual forage yield showed that the effectiveness of Gafsa rock phosphate was equivalent to that of soluble phosphates in the long term. Soluble phosphates and liming modified the botanical composition of natural Campos grassland in the long term, but floristic diversity was not altered. [ABSTRACT FROM AUTHOR]

The wide climatic and lithological variability observed in drylands form soils with peculiar characteristics, whose phosphorus (P) dynamics is poorly understood. In this study, we used 93 samples from the surface layer of soils located in tropical drylands in northeastern Brazil, to estimate the effects of climate, land use, parent material, topography and altitude on soil P availability. Our results indicated that the climate affected the availability of P in the soil by its effect in the dynamics of pH values. The increase in pH values in the most arid environments explained 21.9% of the increase in P availability in the soils. We observed that the P available content in soils originated from river sediments was 286, 202 and 168% higher than those found in soils from sedimentary, igneous and metamorphic rocks, respectively. We observed that agricultural cultivation (>20 years) and pasture (>20 years) increased the available P content in the soil by 60 and 51%, respectively, when compared to the reference native forest. We observed that soils located in flat and gently wavy topography had the highest contents of P. The results of our study can be useful for the sustainable use of soils in tropical drylands. • Climate affects the pH values and the availability of P in the soil in drylands. • Soils originated from river sediments showed the highest P contents. • Changes in altitude from 230 to 925 m did not affect soil P availability. • Land use affects soil P availability in tropical drylands. • The pH explained 21% of the variability of the available P in soils in drylands. [ABSTRACT FROM AUTHOR]

Wastewater discharge from shrimp farming is one of the main causes of eutrophication in mangrove ecosystems. We investigated the phosphorus (P) geochemistry in mangrove soils affected by shrimp farming effluents by carrying out a seasonal study of two mangrove forests (a control site (CS); a site affected by shrimp farm effluents (SF)). We determined the soil pH, redox potential (Eh), total organic carbon (TOC), total phosphorus (TP), and dissolved P. We also carried out sequential extraction of the P-solid phases. In SF, the effluents affected the soil physicochemical conditions, resulting in lower Eh and higher pH, as well as lower TOC and higher TP than in CS. Organic P forms were dominant in both sites and seasons, although to a lesser extent in SF. The lower TOC in SF was related to the increased microbial activity and organic matter decomposition caused by fertilization. The higher amounts of P oxides in SF suggest that the effluents alter the dominance of iron and sulfate reduction in mangrove soils, generating more reactive Fe that is available for bonding to phosphates. Strong TP losses were recorded in both sites during the dry season, in association with increased amounts of exchangeable and dissolved P. The higher bioavailability of P during the dry season may be attributed to increased mineralization of organic matter and dissolution of Ca-P in response to more oxidizing and acidic conditions. The P loss has significant environmental implications regarding eutrophication and marine productivity. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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To evaluate the effectiveness of multielement extraction of Mehlich 1 and Mehlich 3 solutions in soils from southern Brazil, correlation studies are needed. The amounts of phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), copper (Cu), and zinc (Zn) extracted with Mehlich 1 solution, 1.0 M potassium chloride (KCl), and 0.1 M hydrochloric acid (HCl) for representative soil types of the Rio Grande do Sul state (Brazil) were compared with those extracted with Mehlich 3 solution. The amount of nutrients extracted with different methods indicated high correlation coefficients. On average, Mehlich 3 solution extracted greater amounts of P (50%) and K (20%) than Mehlich 1 solution. Calcium amounts extracted with all solutions were similar. Magnesium amounts extracted with Mehlich 3 solution were on average 20% less than the amounts extracted with 1.0 M KCl solution. Mehlich 3 solution extracted similar amounts of Cu as the 0.1 M HCl but lesser amounts of Zn. Simultaneous multielement soil-test methods such as Mehlich 1 and Mehlich 3 solutions are efficient in soils from southern Brazil and are a feasible alternative to improving the efficiency of soil-testing laboratories. [ABSTRACT FROM PUBLISHER]

Soil clay content is an important soil attribute and has been used to classification of phosphorus status in the soil in order to determinate the needing of phosphorus amounts to be applied to crops production. The aim of this research was to adjust the method for soil clay content determination, adopted by the laboratories of Southern Brazil (ROLAS-RS/SC), for soil clay content evaluation in Rondônia soils. The study was conducted using 50 soil samples from Rondônia State with wide range clay content. It was tested shaking periods (1.5, 2.0 and 2.5h) associated with periods for soil particles decantation (1.5 and 2.0h) to correlate with the standard method for soil texture testing, known as the pipette method. Clay content determined through this method was significantly correlated with pipette method. The better treatment was the combination of 2.0h of shaking and 1.5h of decantation, resulted in total period of 3.5h, which reduced the period to determine the soil clay content without loss of accuracy. [ABSTRACT FROM AUTHOR]

This study investigated changes in diversity of shrub-tree layer, leaf decomposition rates, nutrient release and soil NO fluxes of a Brazilian savanna (cerrado sensu stricto) under N, P and N plus P additions. Simultaneous addition of N and P affected density, dominance, richness and diversity patterns more significantly than addition of N or P separately. Leaf litter decomposition rates increased in P and NP plots but did not differ in N plots in comparison to control plots. N addition increased N mass loss, while the combined addition of N and P resulted in an immobilization of N in leaf litter. Soil NO emissions were also higher when N was applied without P. The results indicate that if the availability of P is not increased proportionally to the availability of N, the losses of N are intensified. [Copyright &y& Elsevier]

Upland rice is an important crop in Brazilian agriculture and phosphorus (P) deficiency is one of the most yield limiting factors for this crop. A greenhouse experiment was carried out with the objective of evaluating response of upland rice to P rate and sources. The treatment consisted five P rates: 0, 25, 50, 100, and 200 mg dm-3 supplied through four P sources: Araxa, Catalao, Irece, and Lagamar. The soil used in the experiment was a Typic Hapludox. Rice grain yield, shoot dry weight, and root dry weight was significantly increased with increasing resin extractable P in the soil. Maximum shoot dry weight and grain yield was achieved with resin extractable P of 30 mg P dm-3. However, root dry weight increased linearly with increasing P concentration in the range of 4 to 72 mg dm-3. Shoot dry weight, grain yield, and root dry weight increased significantly in a quadratic fashion with increasing P concentration in the shoot. Rice yield and P uptake were not affected significantly with P sources. Grain Cd concentration also was significantly affected by P rates but did not exceed the permissible concentration for human consumption, according to Brazilian food legislation. [ABSTRACT FROM AUTHOR]

The Mehlich 1 (M1) soil-test method has been used for soil phosphorus (P) extraction in southern Brazil. The objective of this work was to compare M1, Mehlich 3 (M3), and ionic exchange resin (resin) soil-test methods to evaluate the soil P available for crops and grasses in soils amended with phosphate rock (PR). Oxisol and Alfisol received triple superphosphate (TS) and PR. The M1 solution extracted greater P amounts in soils amended with PR compared with the M3 solution and resin methods. Lesser P amounts were extracted with the M3 solution. Crops yields were better associated with the P amounts extracted with M3 and resin methods in soils amended with PR. The results showed that M1 overestimates soil P availability to plants in soils amended with PR; the M3 solution best estimated the soil P available for crops and grasses in soils amended with PR. [ABSTRACT FROM AUTHOR]

Phosphorus adsorption in ten soils from Pernambuco State and its relations with physical and chemical parameters. An experiment was carried out to study phosphorus (P) adsorption in ten soil samples from Pernambuco State, Northeastern Brazil. The relationship between physical and chemical soil attributes and P adsorption isotherms were also evaluated. The results showed that maximum phosphorus adsorption capacity (MPAC), remaining P (Rem-P) and the k constant of the Freundlich equation are reliable variables to characterize P adsorption by the soils. Due to its easy determination, Rem-P is the best indicated variable. The parameters of P adsorption MPAC, Rem-P and the k constant of the Freundlich equation showed correlation (p < 0.01) with the chemical attributes potential acidity (H+Al), exchangeable aluminum (Al), exchangeable cation capacity (ECC) and with the physical attributes clay and field capacity (FC). The variables FC, Rem-P, H+Al, Al, ECC and clay, among the chemical and physical attributes evaluated, allowed estimating the MPAC value on the studied soils. The P adsorption energy and the n constant of the Freundlich isotherm were not reliable indicators of the P soil adsorption power. [ABSTRACT FROM AUTHOR]

To select and evaluate the effectiveness of multi-element soil-test methods for extracting plant-available phosphorus (P), correlation studies are needed. Under natural conditions, corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] were sequentially cultivated in 9-L microplots for 45 days to determine the amount of P that would be absorbed from 49 diverse soils of Rio Grande do Sul State in southern Brazil. Before planting, soil P was extracted with Mehlich 1 solution, Mehlich 3 solution, and ion- exchange resin. The abilities of Mehlich 1, Mehlich 3, and resin to extract plant-available P were then compared. The coefficients of determination obtained between plant P and the amounts extracted by Mehlich 1, Mehlich 3, and resin were 0.59, 0.45, and 0.59, respectively, for corn and 0.57, 0.57, and 0.52 for soybean. Soil P extracted by the three methods was highly correlated; however, the amount of P extracted by the methods was affected by the clay content of the soils. As the clay content increased, the amount of P extracted by the resin also increased, whereas P extracted by the Mehlich 3 solution decreased. Because soil clay content influences extractable P values, soil clay classes are needed to properly calibrate soil P status and fertilizer recommendations for corn and soybean grown on these soils. [ABSTRACT FROM AUTHOR]

The Brazilian Atlantic Forest is one of the 25 biodiversity hot spots in the world. Although the diversity of its fauna and flora has been studied fairly well, little is known of its microbial communities. In this work, we analyzed the Atlantic Forest ecosystem to determine its bacterial biodiversity, using 16S rRNA gene sequencing, and correlated changes in deduced taxonomic profiles with the physicochemical characteristics of the soil. DNAs were purified from soil samples, and the 16S rRNA gene was amplified to construct libraries. Comparison of 754 independent 16S rRNA gene sequences from 10 soil samples collected along a transect in an altitude gradient showed the prevalence of Acidobacteria (63%), followed by Proteobacteria (25.2%), Gemmatimonadetes (1.6%), Actinobacteria (1.2%), Bacteroidetes (1%), Chioroflexi (0.66%), Nitrospira (0.4%), Planctomycetes (0.4%), Firmicutes (0.26%), and OP10 (0.13%). Forty-eight sequences (6.5%) represented unidentified bacteria. The Shannon diversity indices of the samples varied from 4.12 to 3.57, indicating that the soils have a high level of diversity. Statistical analysis showed that the bacterial diversity is influenced by factors such as altitude, Ca2+/Mg2+ ratio, and Al3+ and phosphorus content, which also affected the diversity within the same lineage. In the samples analyzed, pH had no significant impact on diversity. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate the effect of different sources and doses of phosphate fertilizers on the nutrient content of crop melon grown in a continuously fertilized Orthic Latosol Quratzarenic Neosol, at Chapada do Apodi, Rio Grande do Norte, Brazil. The study was carried out in the experimental area of the company "Agrícola Cajazeiras", located in Icapuí, Ceara, Brazil, in 2002. The treatments consisted of the application of increasing doses of phosphorus (0, 80, 160, 240 and 320 kg ha-1 P2O5) in the sources: 1) Natural Phosphate Gafsa-GF (Tunisia), 2) Natural Phosphate Fosbahia-FB (Brazil); 3) Single Superphosphate-SS, and 4) Triple Superphosphate-ST. Yellow-hybrid Gold Mine melon was used as test plant. Phosphorus levels in the soil samples ranged from 105 to 147 mg dm-3. Split block design was used in the experiment. Tissues of the aerial part of the plant were evaluated by checking the levels of N, P, K, Ca, Mg, S, Na, Fe, Zn, Mn and Cu of the petiole and leaf blade. It was concluded that the use of natural P sources such as fosbahia and Gafsa in a continuously fertilized Orthic Latosol Qurtzarenic Neosol is a viable alternative compared to very soluble sources, such as triple and simple super phosphate. On the other hand, the application of high levels of phosphate fertilizers in continuously fertilized Orthic Latosol Qurtzarenic Neosol leads to negative correlations between the Mg and Ca leaf levels and melon productivity. [ABSTRACT FROM AUTHOR]

Abstract: It is well known that termites enrich organic matter in their nests and alter its properties, but their influence on phosphorus forms is less clear. The aim of our study was to quantify and systemize phosphorus forms in different nest parts (outer wall, inner wall, and central part) of termites of varying feeding guilds and soils in seven dominant Brazilian ecosystems. Organic (Po) and inorganic P (Pi) were analyzed after sequential extraction of six labile and stable P fractions in samples from the Amazon region (Terra firme, and Várzea and Igapó floodplains), the Pantanal, the Atlantic rain forest (Mata Atlântica), the Cerrado and the Caatinga. In addition, selected alkaline extracts were characterized by means of liquid-state 31P NMR spectroscopy. The central part of termite nests contained between 275 and 1871mgkg−1 total P, dominated by Pi in nests of soil/wood interface-feeder termites, but with balanced Po and Pi contents in nests of wood-feeding termites. All Po fractions, and, in most nests, also labile Pi forms were enriched in termite mounds in comparison to soils. The P enrichment was most pronounced in nests of the Terra firme (enrichment factors for labile Pi forms and for Po fractions were 1.7–36.5 and 1.1–16.8, respectively), and the Igapó (labile Pi: 4.1–34.0; Po: 1.1–25.7) where the total P content of the soil was the lowest with 141 and 171mgkg−1. Nests of wood-feeding termites mainly accumulated highly labile resin-Pi (enrichment factor 10.5–36.5) and partially the stable HClconc-Pi fractions, apart from Po, which can be all attributed to the organic food source and food digestion. The soil/wood interface-feeder termites had more variations in their nests, but in general had higher portions of P bonded to minerals. Hence, we conclude that (i) termite activity results in a gross enrichment of labile P forms in the nests, (ii) the P composition in termite nests reflects the major feeding guild, and (iii) the degree of this P enrichment is partly driven by the P stock in the soil. [Copyright &y& Elsevier]

Melon (Cucumis melo L.) culture has a great economic importance in the State of Ceará, Brazil, especially for fruit exportation. The use of dry or green coconut powder as a substrate composition associated with arbuscular mycorrhizal fungi inoculation is a recommended procedure, because it has a low cost and is a natural biodegradable substrate. Arbuscular mycorrhizal soil inoculation makes seedlings more resistant to transplanting and increase nutrients absorption capacity, especially phosphorus.The objective of this work was to evaluate different substrate concentrations (dry and green coconut powder and soil) on melon growth arbuscular mycorrhizal colonization under greenhouse conditions. A randomized statistical design was adopted, with ten treatments and four replications. Thirty days after germination plants were harvested and analyzed for their growth and microbiological variables and shoot nutrients content. Substrates compositions with 30% of dry or green coconut powder plus 70% soil inoculated and with AMF increased melon growth. [ABSTRACT FROM AUTHOR]

The current soil test method used to evaluate soil phosphorus and potassium available to the plants in soils from Rio Grande do Sul e Santa Catarina state is the Mehlich-1 solution. The soil test methods studies for these nutrients were conducted based on the conventional soil tillage. The aim of this work was to compare the soil phosphorus and potassium amounts extracted by the Mehlich-1 solution and the nutrients amounts extracted by the Mehlich-3 solution, and resin membrane in soils from the Rio Grande do Sul state, under no tillage soil system and nutrients crop response. The phosphorus amounts extracted by the resin method and by the Mehlich-3 solution were higher than that those extracted by the Mehlich-1 solution in both of them sampling depth. The correlation coefficients among the phosphorus amounts extracted by the methods were high association degree. The potassium amounts extracted by the methods were similar, and the correlation coefficients among the potassium amounts extracted by the methods were high association degree in all soil sampling depth. The soil testing methods that have studied in this work are efficient for soil phosphorus and potassium extraction in soils under no tillage; however, the lowest soil phosphorus amounts extracted by the Mehlich-1 solution, increase the laboratory errors. [ABSTRACT FROM AUTHOR]

Abstract: No-tillage systems lead to physical, chemical and biological changes in soil. Soil fertility is responsive to changes in tillage as it depends on nutrient status, soil water content and biological characteristics. This work aimed to determine long term changes in phosphorus forms and availability in the profile of two tropical soils under conventional and no-till systems, and to discuss the significance of these changes on plant growth and demand for P fertilizers. Undisturbed soil cores with 20cm in diameter were collected to a depth of 40cm, accommodated in PVC tubes and taken to a greenhouse, where the experiment was conducted. Two soils were collected in Central Brazil, in areas under Cerrado. Both soils had been cropped for at least 10 years under conventional tillage and no-till. In the greenhouse, pots received phosphorus fertilization or not at 43.7kgha−1, and soybean was grown for 60 days, when soil P fractions were determined. Labile P fractions in the soil profile were not affected by management systems, and there was no accumulation of available P under no-till. A large amount of P added as fertilizer was adsorbed in soil and remained in moderately labile fractions, mainly on uppermost soil layers. Therefore, the phosphate fertilizer has promoted P accumulation on less available fractions in soil, remaining P on the soil after crop harvest. Eventually this phosphorus could migrate to more labile fractions and be available for crops grown in succession. [Copyright &y& Elsevier]

Abstract: This work aimed to evaluate the impacts of the organic fertilization and the use of green manure (GrM) on the different soil P fractions in areas under organic agriculture in the municipality of Ubajara, state of Ceará, Brazil. The work was carried out in an organically cultivated farm situated in the Ubajara municipality, state of Ceará, Brazil. Soil samples of a sandy soil were collected at the 0- to 5-, 5- to 10-, 10- to 20-, 20- to 40- and 40- to 50-cm layers in areas of Caribbean cherry with (+) and without (−) previous incorporation of GrM in the rows (+GrMr and −GrMr) and between-rows (+GrMb-row and −GrMb-row). Area under natural vegetation (NV) was also sampled and considered as reference. P fractionation was performed by using a sequential extraction scheme adapted from Hedley. The cultivated systems presented higher P contents than NV, mainly in the most labile P pool (res-Pi+NaHCO3-P), indicating that organic management favoured greater P cycling of this fraction. In the cultivated areas labile P pool accounted for 20, 17, 21 and 27% of sum of soil total P in the −GrMr, −GrMb-row, +GrMr and +GrMb-row, respectively. There was an increment of 86% in the organic P pool in the organically cultivated areas in relation to the NV. The organic management promoted an increase on the available-P forms by avoiding and/or decreasing the rate of transformation of the Pi in more stable P forms, enhancing the P cycling. The use of green manure promoted increase on the most labile P pool (Resin-P+NaHCO3-P) and seems to contribute to the P incorporation into biological cycle. On the other hand, the risks of P losses in the organically managed areas should be considered and suggest a scientific remark to farmers for a better management of organic farming in sandy soils. [Copyright &y& Elsevier]

The municipality of Paracatu (Brazil) is notorious for its large irrigated agricultural area and by abnormal arsenic (As) levels in selected soils of the region. Concerns regarding As exposure via ingestion of water and food are frequent, yet little is known about the behavior of arsenic in irrigated agricultural soils, as well as on As bioaccessibility/bioavailability in agroecosystems of this region. This work evaluated total and available As in agricultural soils cultivated under irrigation and in soils under native vegetation in Paracatu. We also assessed reactive arsenic fractions and As bioaccessibility in the soil, as well as arsenic levels in plant shoots to estimate As risks in these agroecosystems. Soil (different depths) and plant tissue samples were collected in 6 irrigated agricultural areas (CA1 to CA6) and 4 reference areas (RA1 to RA4). Total soil-As did not differ between soil depths, reinforcing that the source of As in agricultural soils is natural. This was evident when counterpointing arsenic and phosphorus contents at different soil depths, as both accumulate on the surface of oxidic soils when added to agroecosystems by anthropogenic routes (e.g., phosphate fertilization for P and irrigation for As). Available As levels in soils and plants were very small (below detection limit). Furthermore, all soils presented very low oral As bioaccessibility. Our findings revealed that the irrigated soils are not As polluted due to the low enrichment and accumulation of arsenic, as well as the prevalence of low ecological risks. There is no non-carcinogenic risk for the local population, except for children in RA2. The estimated carcinogenic risk for children followed the order RA2 > CA3 > CA4 > RA3 > CA2, and for adults, RA2 > CA3. Ultimately, the strategy of comparing the behavior of P and As in the soils of this study proved to be efficient in showing that there are no major risks to humans and the environment in the investigated area. However, periodic monitoring of As bioavailability in these areas is recommended. [Display omitted] • Irrigation water is not a relevant source of As in agricultural soils of Paracatu. • High As contents in agricultural soils are of geogenic origin. • As is not bioavailable for plants, ensuring food safety. • All evaluated soils had very low As oral bioaccessibility. • Cultivated areas present low to moderate ecological risk. [ABSTRACT FROM AUTHOR]

The area under no tillage system largely increased in the last decade in southern Brazil. The increase in total phosphorus (P), mainly in the topsoil layer in no-tillage management, is distributed in different inorganic and organic forms. The [SUP31]p nuclear magnetic resonance (NMR) technique can improve the understanding of the dynamics of phosphorus by identifying the structure of the major groups of this element in soils. This research determined the organic and inorganic phosphorus groups, identified by NMR and by chemical analysis in three subtropical soils under conventional and no-tillage systems. Samples of two soil layers from three long-term experiments located in the state of Rio Grande do Sul, southern Brazil, were used. The first experiment was set up in 1979, in a very clayey Rhodic Hapludox; the second, in 1983, in a clayey Rhodic Hapludox, and the third, in 1985, in a sandy clay loam Rhodic Paleudult. Total, inorganic, and organic P, biomass-associated and NaHCO[SUB3] extracted P were determined by chemical analysis and the NaOH + EDTA extract was submitted to [SUP31]p NMR for organic and inorganic determination. There was an overestimation of the organic phosphate content by the ignition method when compared with the MR in surface-active soils (Hapludoxes). The NMR method allowed a good characterization of organic and inorganic phosphate groups in soils. Inorganic orthophosphate was the dominant P form; the organic P portion was higher in the low surface-active (Paleudult) soil, with a dominance of monoester over diester P, independently of soil type, tillage, or depth. A significant positive correlation was found between diester and microbial biomass P content. [ABSTRACT FROM AUTHOR]

The article examines the influence of tropical forest conversion to grazed cattle pasture in the Brazil's Amazon forest on different forms of nitrogen and phosphorus in soil solution and stream water. It compares two pairs of watersheds containing streams that drained land in either forest or pasture at Fazenda Nova Vida, a cattle ranch in Rondonia. Results indicate forest soil solution having higher concentrations of nitrate than pasture, but with same concentrations of ammonium and phosphate.

• Sugarcane straw maintenance on the field reduces the use of inorganic P sources. • Total removal of residues results in soil P deficiency after six crop cycles. • Inorganic P extracted by 0.1 mol L−1 NaOH is the sink of P derived from straw. • High amount of straw results in negligible role of organic P on plant nutrition. Brazil is the world's largest sugarcane producer. This crop leaves huge amounts of straw behind which have to be managed with innovative approaches. In this study, a field experiment was carried out over six successive years of sugarcane harvests to evaluate the effect of straw maintenance on the field on changes in soil phosphorus (P) fractions. Four straw maintenance rates were tested: (i) maintaining 15 Mg ha−1 (SM15); (ii) maintaining 10 Mg ha−1 (SM10); (iii) maintaining 5 Mg ha−1 (SM5), and (iv) maintaining 0 Mg ha−1 (SM0). Our results showed that low maintenance of straw (SM5) resulted in the highest amount of P extracted by anion exchange resin and inorganic P extracted by 0.5 mol L−1 NaHCO 3 in 0−5 and 5−10 cm soil depths. While total removal of residues resulted in soil P deficiency after six crop cycles, keeping straw on the soil surface at the rate of 5 Mg ha−1 supports plant growth without the need for P fertilizer application. We detected inorganic P extracted by 0.1 mol L−1 NaOH as the sink of P derived from straw since it was the only P fraction which increased with increasing straw on the soil surface. Non-labile P fractions were not influenced by straw maintenance rates in all depths. This is a promising result since it shows that P derived from straw does not accumulate in non-labile P fractions which are not plant available. Inorganic P was not influenced by straw removal rates and total P was only changed in 0−5 cm soil layer, while organic P was affected in all depths. We observed that organic P is available to sugarcane plants under SM0, SM5, and SM10, while under SM15, organic P does not play a role in sugarcane nutrition. [ABSTRACT FROM AUTHOR]

• The application of vinasse reduced the pH and surface availability of nutrients. • The application of vinasse increased the availability of K+ and labile P with depth. • Cultivation without burning with straw deposition did not increase P content. • The maintenance of straw on the soil surface reduces the pH values. • All cultivation systems were efficient in forming the legacy of P in the soil. Ethanol is recognized worldwide as a clean and renewable energy source. In tropical and subtropical countries, it is produced from sugarcane (Saccharum officinarum). In this study, we investigated the effects of sugarcane management systems: a) burning of sugarcane for harvest for 37 years (SCB37); b) burning of sugarcane for 3 years after 5 years of fallow (SCB3); c) sugarcane field without burning for harvest for 3 years (SCWB), and d) burning for harvest with the application of vinasse for 3 years (SCV), on soil fertility and accumulation of organic and inorganic fractions of phosphorus (P) in sugarcane crops for bioenergy production in south-east Brazil. Soil samples were collected at depths of 0–5, 5–10, 10–20, and 20–40 cm between planting rows in each management system and submitted for evaluation of soil fertility and accumulation of P fractions via sequential fractionation. We observed that application of vinasse reduced the pH (3.7–4.2) and the availability of Ca2+, Mg2+, and K+ on the surface, associated with the increase in Al3+ content and potential acidity. However, its use increased the availability of K+ and inorganic P content of higher lability (extracted with NaHCO 3) in the subsurface. The maintenance of straw on the surface promoted reductions in pH values and an increase in the potential acidity and was inefficient in the accumulation of organic and inorganic fractions of P, compared to the system with the application of vinasse. Overall, we observed that the moderately labile fraction (organic and inorganic) represented on average 60 % (higher participation) of the total P content of soil in the experimental areas and was more significant in the soil under vinasse application and less evident in the treatments without burning and in the 3-year burning. This fraction can represent an important reserve of P (legacy) for the crops, reducing the use of phosphate mineral fertilizers over the years. Our findings are important for the selection and implementation of efficient and sustainable sugarcane cultivation systems, with implications for the ethanol industry to meet the growing demand for renewable fuel in the world. [ABSTRACT FROM AUTHOR]

Exploiting native soil phosphorus (P) and the large reservoirs of residual P accumulated over decades of cultivation, namely "legacy P", has great potential to overcome the high demand of P fertilisers in Brazilian cropping systems. Long-term field experiments have shown that a large proportion (> 70%) of the surplus P added via fertilisers remains in the soil, mainly in forms not readily available to crops. An important issue is if the amount of legacy P mobilized from soil is sufficient for the crop nutritional demand and over how long this stored soil P can be effectively 'mined' by crops in a profitable way. Here we mapped the spatial–temporal distribution of legacy P over the past 50 years, and discussed possible agricultural practices that could increase soil legacy P usage by plants in Brazil. Mineral fertiliser and manure applications have resulted in ~ 33.4 Tg of legacy P accumulated in the agricultural soils from 1967 to 2016, with a current annual surplus rate of 1.6 Tg. Following this same rate, soil legacy P may reach up to 106.5 Tg by 2050. Agricultural management practices to enhance soil legacy P usage by crops includes increasing soil pH by liming, crop rotation, double-cropping, inter-season cover crops, no-tillage system and use of modern fertilisers, in addition to more efficient crop varieties and inoculation with P solubilising microorganisms. The adoption of these practices could increase the use efficiency of P, substantially reducing the new input of fertilisers and thus save up to 31.8 Tg of P fertiliser use (US$ 20.8 billion) in the coming decades. Therefore, exploring soil legacy P is imperative to reduce the demand for mineral fertilisers while promoting long-term P sustainability in Brazil. [ABSTRACT FROM AUTHOR]