Nitrogen Content and Use Efficiency of Sweet Sorghum Grown in the Lower Midwest

Abstract

Optimizing N fertilizer inputs is imperative for improving sweet sorghum [Sorghum bicolor (L.) Moench] yields and biofuel feedstock system efficiency. A 2‐yr study was conducted to determine the physiological N‐use efficiency (NUE) response in sweet sorghum's ethanol yield of stem juice, bagasse, and total ethanol yield (TEY). Two sweet sorghum cultivars (‘Dale’ and ‘Top 76–6’) were fertilized at five N fertilizer rates (0, 56, 112, 168, and 224 kg ha−1). At harvest, the stem juice and bagasse yields were measured then analyzed for the corresponding N concentrations and N contents. Whole‐plant N recovery efficiency ranged from −1.5 to 57.6% across both years, with a significant N rate effect only in one study year. The NUE of juice ethanol yield only demonstrated an N response in the second year, whereas the NUE of lignocellulosic ethanol yield was greatest at the 56 kg ha−1 fertilizer rate each year. The NUE of total theoretical ethanol yield, determined as the sum of juice and bagasse conversion to ethanol, averaged 169 L EtOH kg−1 N across both years and was greatest at the 56 kg N ha−1 fertilizer rate in both years, and decreased at N rates exceeding 56 kg ha−1 in only one of the years. This study revealed that although sweet sorghum ethanol yields increased with N fertilizer application, NUE was greatest with low N fertilizer rates, consistent with previous research indicating that sweet sorghum is an appropriate biofuel feedstock for production in low‐input systems or on marginal lands. Core Ideas Nitrogen recovery and use efficiencies of sweet sorghum juice and bagasse were measured for two years in Missouri. Nitrogen recovery efficiency was greatest in one study year when 224 kg N ha−1 was applied, with no differences in recovery in the second year. The N use efficiency of estimated total ethanol yield was greatest at 56 kg N ha−1.

Ecosystem‐scale biogeochemical fluxes from three bioenergy crop candidates: How energy sorghum compares to maize and miscanthus

“…As a result, with higher soil moisture under energy sorghum, the mid‐season peak in N 2 O fluxes was higher for energy sorghum than maize, leading to comparable cumulative growing season N 2 O fluxes for the two crops. Recent evidence also suggests that optimum N fertilization rates for energy sorghum are approximately 56 kg N ha −1 (Maw et al, 2019; Schetter et al, 2020), which is closer to the rate applied to miscanthus in this study. It is therefore likely that our energy sorghum fertilization rate exceeded plant N requirements, and thus we would expect N 2 O losses to be reduced with less N addition in future.…”

Photoperiod Sensitive Energy Sorghum Responses to Environmental and Nitrogen Variabilities

“…This study showed a similar range of PNUE (78.1 -256.4 kg DM kg -1 ) to the reports from Grennel et al (2014) [64] and Maw et al (2017) [34], and the PNUE likely improved with the low N input [34,65,66]. Although the N effect on NIE and NRE was not significant in this study, the better NIE and NRE likely occurred at the low N-rate [34,56,65,66,69]. Many studies have shown that the biomass sorghum has a low N fertilizer requirement (mostly < 120 kg-N ha -1 ) for optimizing biomass yield with desirable feedstock quality for biofuel productions [29,56,57,[67][68][69].…”

“…Although the N effect on NIE and NRE was not significant in this study, the better NIE and NRE likely occurred at the low N-rate [34,56,65,66,69]. Many studies have shown that the biomass sorghum has a low N fertilizer requirement (mostly < 120 kg-N ha −1 ) for optimizing biomass yield with desirable feedstock quality for biofuel productions [29,56,57,67–69]. Moreover, the biomass yield, PNUE, and NIE can be further improved by extending the growing season [11,12,31].…”

Sweet Sorghum Genotypes Tolerant and Sensitive to Nitrogen Stress Select Distinct Root Endosphere and Rhizosphere Bacterial Communities

“…However, most studies focused on comparing plants growing under high-N versus low-N conditions, while the microbiome changes between different plant genotypes in the context of varying soil N levels has not been widely investigated. In sorghum, there is a huge variation in tolerance to N stress between genotypes [ 28 ]. Despite the fact that root-associated microbial communities of sorghum change between N-levels [ 24 , 26 , 27 ], the natural variability of the microbiome between N-stress tolerant and sensitive sorghum genotypes is unclear.…”