Determining Effects of Sowing Time and Nitrogen Fertilizer Rate on Brix of Sweet Sorghum Using a Gear-Type Extractor

Abstract

Sweet sorghum is an attractive energy crop, but the short harvest window and the poor storability of stalks and sugar juices are obstacles in the production of ethanol from sweet sorghum. The sugar content and harvest window of sweet sorghum are very important for ethanol yield and the operating rate of an ethanol production plant. To avoid sugar degradation, the sugar content of sweet sorghum juice needs to be measured immediately after juice extraction from the whole plant. A gear-type extractor suitable for the whole sweet sorghum plant was designed, fabricated, and tested for precise and convenient determination of the sugar content of sweet sorghum. The mean extraction speed of the developed extractor was 9.3 s plant-1. The effects of sowing time and nitrogen fertilizer rate on the sugar content and harvest window were investigated. The sugar contents of sweet sorghum sown on May 1, June 1, and July 3 applying 70 kg ha-1 nitrogen fertilizer and of sweet sorghum sown on May 29 applying 70, 140, and 210 kg ha-1 nitrogen fertilizer were determined using the developed extractor. Brix exceeded 10% for around 30 and 60 days for sweet sorghum sown in May and July, respectively. The sugar content of the juice from sweet sorghum with 70 kg ha-1 N fertilizer applied was higher than that of sweet sorghum with 210 kg ha-1 N fertilizer applied. The results indicate that the later sowing and the lower nitrogen fertilizer rate could prolong the harvest window of sweet sorghum. The harvest window of sweet sorghum used as a feedstock for ethanol production was prolonged to three months by sowing twice and applying 70 kg ha-1 nitrogen fertilizer in one year in Tottori, Japan (35 32' N, 134 10' E).