Dynamic of P Flux in Tropical Acid Soils Fertilized with Humic Acid–Complexed Phosphate

Soils are characterized by high phosphorus (P) immobilization, considering the major limiting factor for agricultural production in Brazil. Phosphate fertilizers complexed with humic acids (HA) have been presented as an alternative to inhibit P immobilization in soils; however, little is known regarding its efficiency or its effect on soil P dynamics when associated with liming. The objective was to investigate labile moderately and non-labile P changes in sandy and clayey soils under application of distinct P sources and liming. Tropical soils were incubated using 200 mg kg−1 of P (simple superphosphate—SSP and SSP + HA), associated or not with calcium oxide. Check-plots were run in both soils without any P addition and/or no liming. After 60, 90, and 180 days of incubation, P contents were fractionated into P inorganic (Pi) and organic (Po), in the following pools: labile (PAER and PBIC), moderately labile (PHCl and PHID-0.1), and non-labile fractions (PHID-0.5 and Presidual). There was a P flux between non-labile and labile fractions, controlled by the use of P fertilizer and liming. In sandy soil, the P addition promoted a clear P flux from non-labile to labile fractions; however, in clayey soil, there was a reverse P flux. The lack of P addition promotes a negative balance in soil with a decrease of labile fractions, mainly when associated with liming. Therefore, inputs are necessary to avoid soil P depletion.