Soil phosphorus distribution in sequentially extracted fractions in tropical coffee-agroecosystems in the Atlantic Forest biome, Southeastern Brazil

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 H2O–Pi; NaHCO3–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, H2O–Pi and NaHCO3–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−1 being the predominant Pi fraction. AGF systems promoted an increment of 8% in the NaHCO3–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.