ARS | Publication request: Nitrogen Requirements for Ethanol Production from Sweet and Photoperiod Sensitive Sorghums in the Southern High Plains

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 25, 2011
Publication Date: January 26, 2011
Citation: Bronson, K.F., Schwartz, R.C., Tamang, P.L., Malapati, A., Johnson, J., Moore-Kucera, J. 2011. Nitrogen requirements for ethanol production from sweet and photoperiod sensitive sorghums in the Southern High Plains. Agronomy Journal. 103(2):431-440.

Interpretive Summary: Sorghum has potential as a bioenergy crop in the Southern High Plains because it can efficiently use water. Nitrogen fertilizer requirements of forage and sweet sorghums grown for ethanol production are not well documented. This study evaluated optimal N fertilizer requirements for ethanol production from sweet and forage sorghum with limited irrigation. Yield of dry matter averaged 5.8 tons per acre and ethanol yield average 198 gallons per acre. Dry matter and ethanol yield responded to nitrogen fertilizer only in 2009. Total enthanol yield was greater with sweet sorghum compared with forage sorghum. The optimum nitrogen fertilizer rate for ethanol and total dry matter production was 96 lbs per acre in 2009. The optimum nitrogen fertilizer rate required to maximize profit was 90 lbs per acre.

Technical Abstract: Sorghum (Sorhum bicolor L.) has high water use efficiency, and is therefore widely cultivated in the Southern High Plains (SHP). Interest in sorghums for biofuel feedstock has increased recently as ethanol demand expands. Unlike grain sorghum, little data are available on N fertilizer requirements for ethanol production from sweet or forage sorghum production. Our objective was to compare ethanol yields and determine optimal N fertilizer needs for ethanol production from sweet sorghum and photoperiod sensitive (PPS) sorghum with limited irrigation in the SHP. Nitrogen fertilizer rates from 0 to 168 N kg ha-1 were tested on four sorghum cultivars (two sweet and two PPS) on Acuff sandy clan loam near Lubbock, Texas in 2008 and 2009. Total dry matter (TDM) yields averaged 12 and 14 Mg ha-1 in 2008 and 2009, respectively. Nitrogen fertilizer response in TDM was observed only in 2009, but bagasse yields responded to N fertilizer in both years. Cellulosic ethanol yields were greater with PPS sorghums than with sweet sorghums in both years. However, total ethanol yields were greater with sweet sorghums than PPS sorghums. Cellulosic ethanol and total ethanol yields responded to N in 2009 only. High pre-plant soil NO3 in 2008 apparently precluded TDM and ethanol yield response to N fertilizer. The optimum argronomic N fertilizer rate for ethanol and TDM across all four sorghums was 108 kg ha-1 respectively in 2009. The optimum N fertilizer rate for maximum profit with $0.70 kg N-1 and $0.50 L-1 ethanol was 101 kg ha-1.