POTENCIAL FORRAGEIRO E PERDAS DE N NA CULTURA CANA-DE-AÇÚCAR EM FUNÇÃO DA ADUBAÇÃO ORGÂNICA E MINERAL.

Abstract

The objective of this study was to evaluate the effects of organic fertilization on the mitigation of N-NH3 volatilization, and on the increase of chemical composition and yield of sugarcane forage. The varieties used were RB 92579, RB 867515 and RB 863129 fertilized with application of nitrogen sources: urea, chicken litter, swine waste (in the dose of 100 kg N ha -1 ). For the analysis of productivity and other parameters were collected plant material in each treatment. The dry matter (DM), crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (FDA), Brix and NDF/Brix ratios were determined. A fistulated wave was used to determine the in situ degradability and, subsequently, the potential degradation of the DM, with incubation periods of 6; 24 and 72 hours (h). For the quantification of losses of N by volatilization, collecting chambers of the SALE type were installed, and for this evaluation only the variety RB 92579 was selected, since it presented higher productivity, lower NDF content and greater potential degradation of DM. The N-NH3 absorption systems were replaced at different time intervals: 24, 48, 72, 96, 144, 216 and 360h after nitrogen fertilization. There was no interaction (P> 0.05) between sources of nitrogen fertilization and varieties for shoot yield and Brix content. There was effect of the variety for MS, where RB 863129, obtained higher content. There was interaction between variety and treatment for PB (P <0.05), where the swine manure concentrated a higher CP content in the variety RB 92579. The interaction was significant for NDF, where RB 863129 obtained higher fiber content for control, urea and chicken bed treatments. The potential degradability of the DM showed an effect (P <0.05) for the variety, source and time, where the variety RB 92579 and the urea and chicken litter treatments presented greater potential degradation of the DM at 72 hours of incubation. Higher losses of N-NH3 were obtained by treatments with urea and chicken litter, observing greater loss intensity until 48 h after fertilization. There was no difference in N losses for treatments with swine and control (P> 0.05). The management of organic fertilizers had similar effects to the mineral fertilization in the chemical-nutritional attributes of sugarcane, and could replace the mineral fertilization. The use of organic fertilizers presented lower losses of N-NH3 in the volatilization process when compared to the mineral source of N. In general, the variety RB 92579 met the criteria for animal feed better.