Phosphorus availability and soybean growth in contrasting oxisols in response to humic acid concentrations combined with phosphate sources

Abstract

Humic acid (HA) use can improve phosphorus (P) availability in soils with high P fixation capacity. The aim of this study was to evaluate soil P availability and soybean growth in both medium-texture (MT) and clayey (CL) Oxisols under humic acid carbon (C-HA) concentrations: 0, 5, 10, 50 and 100 mg kg−1, combined with Araxá phosphate rock (APR) and single superphosphate (SS). Mixtures of C-HA with P sources were incubated for 15 d. In sequence, the soil solution was extracted and analyzed for soil solution C (SSC), soil solution P (SSP) and soil solution electrical conductivity (EC). Soil initial resin-P and pH were determined before soybean sowing and, after harvest, shoot (SDM), root (RDM), total dry matter (TDM), soil residual resin-P and soil pH were determined. In CL fertilized with SS, the addition of C-HA increased SSP by 17%, residual resin-P by 42%, SDM, P and N accumulated in the shoot. Addition of C-HA reduced SSP and initial resin-P in MT treated with SS and increased in 18% residual resin-P in MT fertilized with APR. Effects of HA on soil attributes, soybean growth and nutritional status rely on HA concentration, soil texture and P source used.