Use of nitrogen (15N) of green manure and urea and phosphorus (32P) from mineral fertilizer by corn and bean grown in succession

Abstract

Utilization of nitrogen (15N) of green manure and of urea fertilizer and phosphorus (32P) of the mineral fertilizer by corn and bean grown in succession. Nitrogen and the phosphorus, in most of the situations, are the nutrients applied in larger amounts to corn and bean, and consequently burden the cost of production of those crops and, when managed inadequately, may cause pollution of the water resources. The present work will be carried in the Center of Nuclear Energy in the Agriculture - CENA/USP, located in Piracicaba - SP, in green home, being using pots containing 6 kg soil of a dystrophic Red Latosol. The objectives will be of evaluating the utilization of the nitrogen (15N), mineralized from of the green manure Sun hemp (Crotalaria juncea) and millet (Pennisetum americanum) and of N of the urea, by corn and the residual effect in the bean plant cultivated in succession to the corn; to evaluate the use of the mineral fertilizer phosphorus (32P) by the corn and the residual effect in the bean plant grown subsequently; to discover the N and P interactions on the productivity and on the utilization of these nutritious by the corn and the bean plant; to quantify the utilization of soil N and P by the corn and the bean and, to verify the contribution, separately, of the underground and above ground parts of the Sun hemp and of the millet as N source for the corn and the bean plant grown in succession. The experimental design will be the complete randomized with 24 treatments and four replications, disposed in 2 x 4 x 3 factorial, constituted by the combination of two green manure: Sun hemp and millet labeled with 15N, four rates of N as urea (15N), equivalent to: 0, 60, 120 and 180 kg ha-1 and, three rates of P2O5 as triple super phosphate (32P), equivalent to 0, 60 and 120 kg ha-1. The Sun hemp and the millet plants will be isotopically labeled growing them in pots and applying weekly urea solution enriched in 10% 15N. The following evaluations will be accomplished: Soil - chemical characteristics: pH, Ca, Mg, P, K, S, H+Al, Al, Cu, Fe, Zn, Mn, total-N and mineral-N (N-NH4+ and N-NO3-). Plant - nutritional state, at that time of the flowering, productivity of the corn and of the bean plant dry matter, total P and 32P, total N and 15N, C:N, C:P ratio, lignin/N and poliphenol/N of the green manure at that time of the harvest. The treatments will be evaluated for the dry matter productivity; amount of N derived from the green manure and from the fertilizer urea and the amount of P derived from the mineral fertilizer in the corn and in the bean; utilization efficiency of the N from green manure and of the urea and of P from the mineral fertilizer for the corn and for the bean; percentages of N of the green manure and of the urea and of P of the fertilizer recovered in the soil-plant system and the amount of N and of P in the corn and in the bean from soil.Key words: green manuring, organic matter, 15N, 32P, Zea mays, residual effect.