Optimizing Nitrogen Fertilizer Rates at Distinct In-season Application Moments in Sugarcane

The use of best fertilizer-management practices is one way to increase crop nitrogen use efficiency (NUE) and to reduce environmental impacts. In sugarcane crops, due to the harvest season extension in southeast Brazil (April-November) N fertilization must be adjusted to optimize the N availability during the crop development. Our objective was to assess the influence of N-fertilizer application time and rates on sugarcane and sugar yield, sucrose content, N uptake, and NUE on fields harvested in distinct period (early, middle, and end) of sugarcane harvest season in Brazil. Three experiments were carried out with the same design (split plot) and evaluated for 1st and 2nd ratoon. The main plots consisted in different N-fertilizer application time (0, 30, 60, 90, and 120 days after harvest-DAH), while the split plots were five N rates (0, 50, 100, 150 and 200 kg N ha(-1)). N-fertilizer application time influenced the sugarcane and/or sugar yield at three sites, which the best time to apply N was between 0-60 DAH, in early and 30-90 DAH, in middle period of the harvest season. The N rates that afforded the highest sugarcane yield were 130 (early), 140 (middle) and 100 kg N ha(-1) (end of the harvest season). N-fertilizer application time and rate adjustment optimized N uptake by the sugarcane stalk, reducing 20% on N requirement in early and middle harvest season, and increasing NUE in sugarcane ratoon (10%). This proposed new N management in sugarcane ratoon considers the application time and N rate. (AU)