Nitrogen Requirements for Ethanol Production from Sweet and Photoperiod Sensitive Sorghums in the Southern High Plains

Abstract

Sorghum (Sorghum bicolor L. Moench) 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 clay loam near Lubbock, TX in 2008 and 2009. Total dry matter (TDM) yields averaged 13 Mg ha−1 across years, cultivars, and N rates. 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 preplant soil NO3 in 2008 apparently precluded TDM and ethanol yield response to N fertilizer. The optimum agronomic 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 $.50 L−1 ethanol was 101 kg ha−1

Nitrogen response and water use efficiency of sweet sorghum cultivars

“…Based on this analysis, an optimum N application rate of 90 kg ha -1 is recommended. Similar results were also reported by Erickson et al (2012) and Tamang et al (2011). Nitrogen use efficiency values were estimated relative to yield observed in controlled plot, so that NUE values in Figure 2 represent increment in gross income per unit addition of N fertilizer.…”

“…Similar trends for N response of sweet sorghum were reported by Wiedenfeld (1984) and Tamang et al (2011). Marginal product (MP) curves for biomass yield and ethanol yield are presented in Figure 1A and Figure 1B, respectively.…”

Dedicated Energy Crops and Crop Residues for Bioenergy Feedstocks in the Central and Eastern USA

“…These genetic advancements would be significant in water limited regions, particularly in areas where there is livestock demand for highly digestible forages, and first generation ethanol plants accept sorghum grain. Tamang et al [34] reported an optimum N rate of 108 kg ha −1 for two photoperiod sensitive and two sweet cultivars in the Texas Southern High Plains. Haankuku et al [35] reported an optimal N rate of 100 kg ha −1 in Oklahoma with no supplemental irrigation, but there was no yield response during drought.…”

“…Conservation tillage increased biomass by 11 % during the dry year, but no difference was observed between tillage systems for the wet year [36]. In the Southeast, sweet and photoperiod sensitive sorghums have been examined as potential energy crops due to high biomass production, low N requirements, and drought tolerance relative to corn [34,[36][37][38]. Sweet sorghum has additional benefits of a typically shorter growing season and production of fermentable sugars, although biomass production is reduced compared to photoperiod sensitive sorghum [34,38].…”

“…In the Southeast, sweet and photoperiod sensitive sorghums have been examined as potential energy crops due to high biomass production, low N requirements, and drought tolerance relative to corn [34,[36][37][38]. Sweet sorghum has additional benefits of a typically shorter growing season and production of fermentable sugars, although biomass production is reduced compared to photoperiod sensitive sorghum [34,38]. In addition to the bmr gene, low amylose or waxy endosperm genes and sweet genes are being incorporated and evaluated in current breeding programs that would improve sorghum as a bioenergy feedstock [39].…”