Wheat nutrition and growth as affected by humic acid-phosphate interaction

Low-grade phosphate rock correctly combined with humic acid (HA) has the capacity of single superphosphate (SS) in supplying P to growing wheat (Triticum aestivum L.). The aim of this study was to evaluate wheat dry matter, macro- and micronutrients accumulated in wheat shoot, and the P availability in a Typic Hapludox (Oxisol) under the following humic acid carbon (C-HA) concentrations: 0, 5, 10, 50, and 100 mg kg(-1), which were combined with two P sources, Araxa phosphate rock (APR) and SS. The experiment was carried out under greenhouse conditions. Firstly, soil samples were incubated with combinations of C-HA concentrations and P sources for 15 d; after that, wheat was grown in the pots for 43 d. Shoot dry matter (SDM), root dry matter (RDM), total dry matter (TDM), macro- and micronutrient uptake, and soil resin-P were determined. Addition of C-HA increased RDM growth in soils treated with APR and SS, and improved SDM growth under APR. Accumulation of P, S, Cu, Fe, Mn, and Zn increased in wheat shoots grown in soils treated with APR combined with C-HA concentrations. The addition of 50 mg kg(-1) of C-HA and APR increased RDM and macro- and micronutrient uptake and promoted greater production of SDM in comparison to biomass produced in soil not treated with HA. After wheat cultivation, resin-P contents in soil with APR decreased over C-HA concentrations, which is evidence of adequate supply of P to wheat by APR. The right combination of HA and APR leads to wheat growth and nutrient uptake equivalent to those found for SS.