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Increasing cropping intensity may affect phosphorus (P) recycling through crop residue inputs, which may differ in soils with different productivity, P adsorption capacity, and P fertilization level. In three crop sequences: Soybean (Glycine max L. Merr.) monoculture (S–S), Maize (Zea mays L.) monoculture (M-M), and Wheat (Triticum aestivum L.)/Soybean as a double crop (W/S) in a Vertisol and a Mollisol; we assessed the long-term effect of the crop sequences on soil inorganic P (Pi) and organic P (Po) fractions, and the short-term effect of P fertilization on soil Pi and Po fractions, P uptake, and grain yield. Two P fertilization levels (50 kg P ha−1, and control) were established in 2016 on long-term experiments that included S–S, W/S, and M-M. Bray1-P, as well as total P, Po, and Pi in both the coarse soil (> 53 μm) fraction (CF) and the NaHCO3 extract, and accumulated yield and P uptake were measured. In the long-term, the crop sequences did not change soil P fractions, but Po-CF and Pi-CF showed similar values in both soils, suggesting less soil-type dependence than in other labile P fractions. In the short-term, the P fertilization only increased the extractable Pi fractions (16% in the Mollisol and 25% in the Vertisol), suggesting that P in the CF was not a sink of P fertilizer. Our study showed that P fertilization in different crop sequences may increase labile P fractions and P recycling depending on soil type, a useful tool to develop P fertilization strategies at the crop sequence level. [ABSTRACT FROM AUTHOR]

The purpose of this study was to evaluate how the different phosphorus fractions in soils contribute to plant uptake, based on the combination between the sequential P fractionation developed by Hedley and path analysis. Successive crops were grown on soil samples with different P legacies, taken from the 0.00–0.10 m layer of an untilled Latossolo Vermelho (Rhodic Hapludox). The experimental treatments consisted of three annual P rates (0 kg P ha−1–P0; 157 kg P ha−1–P157; 314 kg P ha−1–P314). In a greenhouse, 15 successive crops of millet, black oat, corn, soybean, crotalaria and rye were grown in pots, with six replications. Phosphorus fractions in the soil were evaluated before the first crop and after the third and 15th crop. At the beginning of cultivation, the labile P fractions were buffered by the less labile P fractions in soils fertilized with the highest P rate (P314). After the 15 crop cycles, labile P was buffered, mainly by labile and non-labile organic P fractions. In soils without previous P fertilization and intermediate fertilizer rates, there was a significant contribution of organic P fractions to the moderately plant-available inorganic P pool. The organic P fraction only contributed to plant nutrition in soils fertilized with high P rates after depletion of the inorganic P pool. The conclusion was drawn that all soil P fractions can potentially provide plants with P, whereas the contribution of these P fractions depends on the P fertilization history. [ABSTRACT FROM AUTHOR]

The aim of this study was used a basic hypothetical structural model with latent variables to analyze the interconnections between the pools of stable P (inorganic P (Pi) and organic P (Po)), labile P (Pi and Po) and available P (Mehlich-1 P) and the pools of organic matter (OM) content and physicochemical properties in tropical soils of differing pedogenesis. We used structural equation modeling for designing models for two groups of soil: (1) mineral soils with low to medium organic matter content and (2) mineral soils with high organic matter content and organic soils. The proposed structural models were consistent with the hypothesis of dependence between the pools of P and organic matter as well as physicochemical properties in tropical soils. In general, stable and labile P pools acted as P sources for the available P pool; furthermore, the strength of these structural relationships was strongly associated with soil organic matter content. Yet the pool of physicochemical properties behaved as a sink of P for the labile P pool, however with a beneficial effect in maintaining the stable P pool. The pools of P and OM are strongly bonded in tropical soils under different pedogenesis. All structural models evidenced that various forms of P in different levels of lability could contribute in keeping the supply of bioavailable P, yet its magnitude would be regulated by P buffer capacity of each soil. [ABSTRACT FROM AUTHOR]

Phosphorus (P) deficiency is one of the most important constraints to food production, particularly in tropical Oxisols. This study aimed to characterize the inorganic and organic P (Pi and Po) fractions in the soil in three smallholding coffee cultivation fields managed under either agroforestry (AGF) or full sun (FSC) agroecosystems. The work was carried out in areas situated at the municipalities of Divino and Araponga in the Zona da Mata in the state of Minas Gerais, southeastern Brazil. Soil P forms including HO-Pi; NaHCO-Pi,Po; NaOH-Pi,Po; diluted HCl-Pi; concentrate HCl-Pi,Po and Residual-P were sequentially extracted in samples from 0 to 5 and 5 to 10-cm soil layers. Together, HO-Pi and NaHCO-Pi accounted on average for only 4% of soil total P in the cultivated soils. HClconc.-Pi ranged from 142.8 to 372.4 mg kg being the predominant Pi fraction. AGF systems promoted an increment of 8% in the NaHCO-Po fraction in relation to the FSC systems in the upper soil layer. The AGF systems increased HClconc.-Po pool in relation to the FSC systems in Divino and Araponga(I) soils, indicating that agroforestry is an important management strategy to increase bioavailable P and for the maintenance of organic P pool. The distribution of inorganic and organic P pools varied among the different study sites, showing that P cycling depends on the inherent characteristic of each agroecosystem. The availability of P to plants in coffee-agroforestry fields is directly associated with the cycling of the organic P pool. [ABSTRACT FROM AUTHOR]