Tillage and phosphorus management effects on enzyme-labile bioactive phosphorus availability in Cerrado Oxisols

Phosphorus (P) is an essential element in crop nutrition, which can be growth limiting or an environmental contaminant, if present in excess. Tillage practices have a direct effect on the behavior and availability of soil P. Sorption and availability of various P forms were evaluated in an incubation–fractionation study of three soils, a Typic Paleudults (CR soil) and two Cerrado Oxisols (Latossolo Vermelho–Amarelo [LVA] and Latossolo Vermelho [LV]) with distinct biogeochemical characteristics and tillage management history. Phosphate and myo-inositol hexakisphosphate (mIPH) were strongly sorbed by the soils. Maximum adsorption capacities (Smax) were 2.2–6.9, 3.3–7.8, and 1.6–19.8 mmol kg− 1 for phosphate in the 0–40 cm depths of the CR, LV, and LVA soils, respectively. For mIPH, Smax were 1.2–3.7, 3.7–5.5, and 4.6–5.2 mmol kg− 1. Saturation indices reflected the long-term effect of repeated manure applications on the Paleudults and the near saturation of its P holding capacity, in contrast to the recently cultivated Cerrado soils. Tillage method appeared to have altered P retention characteristics of the near-surface zone very slightly, while increases in ligand-exchangeable (EEPi) and enzyme-labile organic P (EDTA-PHP) forms were observed in no-till Oxisols. In the Paleudults, added manure P increased bioactive P fractions and P saturation of no-till near-surface soil zone. Estimates of all bioactive P fractions using the ligand-based enzymatic assay showed it to be an effective method for assessing P availability in soil and developing sustainable P management strategies, particularly in Cerrado Oxisols that were low in organic matter while having an extensive P-fixing capacity.