Department of Plant Sciences

The phosphorus (P) utilization of the mineral fertilizer by the corn plants ((Zea mays L.) can be maximized with the appropriate supply of nitrogen (N). The objective of this work was to evaluate the utilization, by corn plant, of phosphorus (P) from ³²P labeled triple superphosphate(TSP-³²P) under different rates, and P from soil, as by crop residues of green manures sunnhemp (Crotalaria juncea L.) or millet (Pennisetum glaucum L.) and different N rates. The experiment was conducted in greenhouse of the Center for Nuclear Energy in Agriculture - CENA/USP, Piracicaba, S. Paulo, Brazil, using pots with 5 kg of soil (Rhodic Dystroferric Hapludox) cerrado phase (savannah). The experimental design was completely randomized, with 32 treatments and four replicates, in a 4x4x2 factorial array. The treatments were combinations of four P rates as TSP-³²P: 0, 0.175, 0.350 and 0.700 g P per pot; four N rates as urea: 0, 0.75, 1.50 and 2.25 g N per pot; and sunnhemp and millet. Green manure dry matter provided 1 g N per pot. Corn plants were evaluated for dry mass yield, P content, accumulated P, and P recovery from TSP-³²P and from soil plus green manures. The P recovery from TSP-³²P increased with the increasing supply of nitrogen and decreased with increasing rates of the TSP. The mineral fertilizer supplied most of the accumulated phosphorus in the corn plants. The recovery by corn plant of the P fertilizer was in average of 13.12 %. The different residues of green manures influenced the assimilation of P of the triple superphosphate by corn plant.