Phosphorus fractions in a lowland production system in subtropical soil under no-tillage

ABSTRACT: Phosphorus (P) is one of the most limiting elements for plant nutrition in tropical and subtropical soils due to its high binding energy on the surface of iron and aluminum oxides and hydroxides. Flooded rice cultivation occurs in lowlands, influencing redox reactions and P dynamics. This study aimed to evaluate the forms of phosphorus and their lability after soil reoxidation subsequent to a period of flooding for irrigated rice cultivation following four seasons of cultivation with soybean-ryegrass and corn-white clover succession in an Albaqualf (Planossolo) fertilized with triple superphosphate under no-tillage. The experiments were conducted in Albaqualf (Planossolo), in a 2 × 2 double factorial scheme, with factor 1 being P fertilization and factor 2 being flooding followed by drainage. Triple superphosphate was used as the P source. One of the experiments consisted of a soybean-ryegrass, and the other consisted of corn-white clover, cultivated for four years, with irrigated rice cultivated in the fifth year. Using TSP increased the soil P-labile fraction by 107 and 114 %, for soybean-ryegrass succession and cornwhite clover succession, respectively. After the end of the flooding period and post-soil drainage, a reduction of 17 and 13 % was observed in the P-labile and P-moderately labile fractions, in soybean-ryegrass, respectively. And the same fractions in the cornwhite clover succession decreased 12 and 5 %, respectively. Using P fertilizer increases the fractions of P-labile, P-moderately labile, and P-less labile in the soil. Soil drainage after rice cultivation reduces the fractions of labile and moderately labile phosphorus in the soil, regardless of the crop succession used.