Sistema de rotação e adubação fosfatada na cultura da cana-de-açúcar no cerrado

Abstract

Considering the possible negative effects caused by sugarcane through the years, culture rotation can yield several benefits, including the improvement of phosphorus use. Low phosphorus availability in the savannahs is a major restriction factor form sugarcane yield in this environment. This study analyzed the effect of culture rotation and phosphate fertilization con sugarcane yield and its technological quality. The test was done in two different soil types, clay and sandy soils. The culture rotation system consisted of soybean or Crotalaria juncea, cultivated for one or two subsequent years. The phosphorus source was magnesium thermo-phosphate, at 170 kg ha-1 P2O5. The experimental design was randomized blocks with split plot as a 5x2 factorial, with: 5 rotation systems in the plots (fallow, soybean for one year, two consecutive years of soybeans, one year with crotalaria or two consecutive years of crotalaria), with or without phosphate fertilization in the split plot and four repetitions. Sugarcane was planted in March 2004, after the rotation management. The sugarcane parameters analyzed were: tillering, stalk biometry, technological analyses (sugarcane POL, syrup BRIX and syrup P2O5), stalk and sugar yield. Chemical analysis of the two soils was done after sugarcane harvest. Sugarcane leaf analysis was done, after 8 months of ratoon growth. The rotation systems affected positively, on both experiments, biometry, stalk yield and P soil level. While phosphate fertilization increased soil phosphorus, magnesium and base saturation levels in both experiments, also increasing P2O5 concentration in the syrup of the first year sugarcane, stalk and sugar yield increases were found only on the sandy soil, for both phosphate fertilization and rotation systems. The best rotation system in this soil was found on two consecutive years of soybeans. However, in the clay soil, the greatest stalk yield was found in areas cultivated for two years with crotalaria. Although phosphate fertilization increased soil P levels in both soils, no differences were observed in leaf P concentration of ratoon sugarcane after 8 months of growth.