Effects of Nitrogen Application on Sweet Sorghum (Sorghum bicolor (L.) Moench) in the Semi-Arid Tropical Zone of India

Sweet sorghum is a multipurpose crop that has great potential as a bioethanol crop. To make an appreciable profit from cultivating sweet sorghum in the semi-arid tropics (SAT), such agronomic practices as nutrient management need to be standardized. The objective of this study is to determine optimum nitrogen (N) rates for maximizing the grain and sugar yields of sweet sorghum during the rainy season in the Indian SAT. During the 2009 and 2010 seasons, the response of sweet sorghum being grown in an Alfisol to the application of six N rates (0, 30, 60, 90, 120, and 150 kg N ha(-1)) was evaluated in Patancheru, Andhra Pradesh, India. The chlorophyll content (SPAD reading), cane fresh weight, and grain dry weight increased significantly in line with higher N rates. The volume of juice also increased significantly, although sugar content (brix reading) did not change in line with higher N rates, consequently resulting in a significant increase in sugar yield as computed from the volume of juice and sugar content. There were smaller differences due to N application during the season when soil fertility was at a medium level under high air temperature. Net income, as estimated from cane fresh weight and grain dry weight, increased at rates up to 90 kg N ha(-1), and higher N rates did not significantly affect productivity or income, but instead caused severe lodging in 150 kg N ha(-1) at the harvest stage. Based on these results, an input of 90-120 kg N ha(-1) could be recommended for maximizing sweet sorghum productivity and farmers' income in the SAT region of India.