Adubação nitrogenada com uréia e adubos verdes na cultura do arroz e efeito residual no feijoeiro / Nitrogen fertilization with urea and green manures in rice crops and its residual effect in bean crop

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The association of green manures and mineral N sources is becoming a promising option for nitrogen fertilizer management, with the objective of recovering the soil fertility, increase of soil organic matter, reduce the loss of mineral N from the readily available sources, and in the case of legume incorporate biologically fixed N to the soil. The objectives of this research were to: (1) evaluate the utilization of N by the rice crop from crotalaria (sunnhemp), millet and urea and its residual effect on bean crop (Phaseolus vulgaris L.) grown in succession; (2) evaluate the contribution of N from the roots and above ground part of these green manures to rice and bean crops, and (3) quantity the N in the plant derived from the green manures in relation to the urea application time (at seeding and topdressing). Experiments were carried out with typic dystrophic Red Latosol (oxisol) in green house at CENA/ USP, in three phases: (a) green manures labeling with 15N, using (NH4)2SO4 enriched with 10 and 5% 15N, for crotalaria and millet, respectively; (b) rice growth in pots containing 4 kg of air dried soil, in completely randomized design with 12 treatments and three replicates, arranged in a 3 x 4 factorial scheme, corresponding to combination of crotalaria, millet and without addition of organic N, with four rates of urea-15N (0; 28.6; 57.2; 85.8 mg N Kg-1), and (c) bean plant growth after rice cultivations. The rice grain productivity was affected positively by the crotalaria when compared to millet and treatment without green manure, with greater effect with increasing mineral N rate. The crotalaria N utilization (18.9%) by the rice plants was more than two times higher than from the millet (7.8%). The urea rates, in the treatments with or without green manure, did not affect the utilization by the rice plants (grains + husk) of N form the fertilizer (53.76% in average). The utilization of green manure roots N by the rice plants was 14.1%, while of above ground parts was 16.8%. With crotalaria, higher utilization of N occurred from urea applied at seeding (61.7%) compared to the top dressed application (47.1%), but this effect was not observed for millet and without addition of green manure. The utilization of green manures residual N by the bean crop was only 3.56% from crotalaria and 3.43% from millet, which were higher than from fertilizer N (2.63%).

ASSUNTO(S)

fertilization immobilization. fertilizantes nitrogenados crotalária nitrogen adubo verde 15n adubação isótopos mineralization n utilization isotope isotopic dilution efficiency feijão arroz uréia.

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