Sugar cane yield in subsequent cycles associated to the residual effect of N and S and their transformations in the soil, on conservation system

Abstract

Considering that the current knowledge on the response of the sugar cane yield to the N and S fertilization was obtained with experiments in only one cycle: plant cane or ratoon crop; that the sugar cane is a semi-perennial grass and as such it is dependent of the energy and nutrient reserves of the root system (roots and rhizomes) in order to sustain the vigor of ratoon plants; considering, also, that the main losses of N from the soil-plant system may occur by nitrate leaching and denitrification in the soil, and ammonia volatilization by foliage, and this last process can explain the reductions in the N content of the sugar cane plants at the end of the cycle; the main objective of this project will be to evaluate the sugar cane yield in conservation system - without burning the cane straw before harvesting and without plowing the soil - in relation to N fertilization applied to the plant cane and ratoon cycle, and the interaction of those N fertilizations in overall yield of sugarcane crop. The transformations of fertilizer-N and - S in the soil-plant system will be evaluated by 15N and 34S stable isotope techniques and it will intend to find out correlation's between them and sugar cane yield. Four field experiments will be carried out, with one cultivar of sugar cane, in soils with different textures. The sugar cane will be planted between January to April 2004, and the experiments will last 4 years. Four doses of N-uréia: 0, 40,80 and 120 kg ha-1 of N applied in the planting furrow, will be tested in the plant cane cycle. There will be microplots with urea- 15N for the determination of the N-fertilizer utilization by plant cane and for evaluations of the residual effect in the subsequent cycles (first and second ratoons). Ammonium sulfate (AS) will be applied in the first ratoon associated to the doses of urea-N applied at planting of sugar cane, at rates of 0, 50, 100 and 150 kg ha-1 of N. Ammonium sulfate will be applied in soil surface onto straw cover. There will be microplots with AS (rate of 100 kg ha-1 of N) labeled with 15N and 34S for the evaluations of N and S utilization by first sugar Gane ratoon plants, as well as of the residual effect in the third crop cycle and for transformations of N and S in the soil. (AU)