UTILIZATION OF NITROGEN FROM CORN PLANT RESIDUES AND GREEN MANURES BY CORN

The quality of commercial crop residues and green manure influences the N mineralization-immobilization rate and the respective use by subsequent crops. With the objective of evaluating N utilization by corn of N from the shoot and root system of sunnhemp (Crotolaria juncea) and millet (Pennicetum americanum) and corn straw, labeled with N-15, a green house experiment was carried out at the Centro de Energia Nuclear na Agricultura (CENA/USP), Piracicaba, S. Paulo, Brazil, in 5 leg pots with dystroferric Red Latosol in a completely randomized design, with four replications and the following six treatments: T-1 = N-15 labeled corn straw (above ground part, except grains) (80 mg kg(-1) N in soil); T-2 = N-15 labeled millet root (30 mg kg(-1) in soil); T-3 = N-15 labeled millet shoot (80 mg kg(-1) N in soil); T-4 = N-15 labeled sunnhemp root (30 mg kg(-1) N in soil); T-5 = N-15 labeled sunnhemp shoot (80 mg kg(-1) N in soil) and T-6 = treatment without addition of organic N source. In the treatments with N-15 labeled root application, unlabeled shoot at the same amount added as in those where labeled shoot was applied, and vice-versa. The roots were incorporated into the soil and shoots left on the surface. To evaluate N absorption from N-15 corn straw (7.35 Mg ha(-1), equivalent to 56 kg ha(-1) N) by corn crop, a field experiment was carried out, in the same area where the soil for the green house experiment had been collected. The amount of corn N derived from, sunnhemp (111.80 mg pot(-1) N) was higher than from millet (30.98 mg pot(-1) N), which in turn higher was than from corn plant residues (11.80 mg pot(-1) N). Sunnhemp resulted in highest nitrogen absorption and dry matter weight of the corn crop. The corn utilized more N from sunnhemp shoot than from roots, but there was no difference in N derived from millet. The N absorption of corn from corn straw was 4.1% of the initial amount in the field experiment.