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Energy sorghum [Sorghum bicolor (L). Moench] is potentially of great significance for bioethanol production because of its high biomass and wide adaptability. In this study, a field experiment was conducted on a semiarid marginal land in Inner Mongolia (39°10′N, 109°53′E), China, to assess the effects of genotypes with similar growth duration and biomass yield levels on chemical composition and theoretical ethanol yield (TEY) in both leaves and stems of four genotypes each of sweet and biomass sorghum in 2013 and 2014. Among all varieties, no significant variation was observed in the biomass yield of leaf (1.81–2.55 Mg ha−1) and stem (3.73–4.87 Mg ha−1), which was relatively low due to the marginal land with low temperature conditions. By contrast, considerable variation was detected in soluble sugars, ash and hexose contents of leaves and stems among the sweet sorghum varieties over two years. Compared with the sweet type, biomass sorghum varieties exhibited significantly lower soluble sugars content but higher cellulose, hemicellulose, and lignin contents in both leaf and stem tissues, resulting in significantly lower hexose and higher pentose contents. Moreover, stems exhibited significantly higher total content of hexose and pentose (725.4 g kg−1) than leaves (642.3 g kg−1) across all varieties, leading to significantly higher TEY of stems than that of leaves. Despite the slightly higher TEY of sweet sorghum, biomass sorghum varieties exhibited particularly stable chemical components and TEY across both experimental years, resulting in greater potential for industrial bioethanol production in this study. Overall, varietal selection was effective in improving the biomass feedstock quality of energy sorghum for biochemical conversion. The findings of this study will help to facilitate industrial bioethanol production from dedicated bioenergy crops.

Increasing demand for renewable energy has stimulated energy crop cultivation on marginal lands with low production potential. This study investigates potential biomass yield of switchgrass (Panicum virgatum L., cv. Blackwell), plant nutrient (nitrogen, N; phosphorus, P; potassium, K) concentration and uptake, N-use efficiency (NUE) and apparent soil N balance in a semiarid rainfed sandy wasteland of Inner Mongolia, China. The aim of this study was to optimize N fertilizer rate and harvest time to produce quality biomass sustainably with minimal soil nutrient removal through harvested crop biomass. Five N rates (0, 60, 120, 180, 240 kg N ha−1) and two harvest times (late summer and early fall) in one-cut system were evaluated in 2015 and 2016. Nitrogen application of 60 kg N ha‒1 significantly increased aboveground plant (AGP) biomass yield by 14.3% vs. control only during early fall harvest in 2016, with no yield response at rates >60 kg N ha−1. AGP nutrient concentration and nutrient uptake increased by increasing N rate, except for P concentration, which decreased. Partial factor productivity (PFP) and agronomic NUE (ANUE) of applied N fertilizer decreased quadratically with N rates >60 kg N ha−1. Apparent soil N budget study revealed an N deficit (0–20 cm depth) in control while N surplus increased as N rate increased which likely boosted NO3- leaching. An early fall harvest exhibited 12.5% higher biomass yield and substantially reduced biomass N and K concentration and uptake relative to late summer harvest. These findings demonstrate that an N input not exceeding 60 kg N ha−1 would be sufficient to optimize biomass yields of Blackwell switchgrass and maintain the soil N balance on a semiarid rainfed sandy wasteland of Inner Mongolia when harvested in early fall. Therefore, N fertilization and harvest time practices should be considered simultaneously in switchgrass production systems for the continuous and sustainable biomass supply with increased feedstock quality and reduced crop fertilizer requirements.

Switchgrass (Panicum virgatum L.) is a perennial warm-season grass which has great potential as a forage or bioenergy crop in marginal land. This study was conducted to determine whether nitrogen (N) fertilization could affect biomass quality of switchgrass harvested in late summer and early fall. The effects of four N fertilizer application rates (0, 60, 120, and 240 kg N ha−1) and two harvest times (late summer and early fall) on the quality components of forage and biofuel feedstock and theoretical ethanol yield (TEY) were investigated on a sandy wasteland (Aridisol) in Inner Mongolia, China during the growing seasons of 2015 and 2016. Soil NO3− content was also examined in response to N application rates. Application of 60 kg N ha−1 significantly increased switchgrass crude protein (CP) content, protein yield, and TEY (p

Switchgrass (Panicum virgatum L.) is a perennial biofuel crop with a high production potential and suitable for growth on marginal land. This study investigates the long-term planting effect of switchgrass on the dynamics of soil moisture, pH, organic carbon (SOC), total nitrogen (TN), nitrate nitrogen (NO₃–-N) and ammonium nitrogen (NH₄⁺-N) for soils to a depth of 90-cm in a sandy wasteland, Inner Mongolia, China. After crop harvesting in 2015, soil samples were collected from under switchgrass stands established in 2006, 2008, and 2009, native mixture, and a control that was virgin sand. Averaged across six layers, soil moisture and pH was significantly higher under the native mixture than switchgrass or virgin sand. However, SOC and TN were significantly higher under the 2006 switchgrass stand when compared with all other vegetation treatments and the control. The SOC and TN increased from 2.37 and 0.26 g kg⁻¹, respectively, for 2009 switchgrass stand, and to 3.21 and 0.42 g kg⁻¹, respectively, for 2006 switchgrass stand. Meanwhile, SOC and TN contents were 2.51 and 0.27 g kg⁻¹, respectively, under the native mixture. The soil beneath switchgrass and native mixture showed the highest NO₃–-N and NH₄⁺-N, respectively. The soil moisture increased with depth while SOC, TN, and NO₃–-N decreased. An obvious trend of increasing moisture, SOC, TN, and mineral N was observed with increasing switchgrass stand age. Thus, growing switchgrass on sandy soils can enhance SOC and TN, improve the availability of mineral N, and generate more appropriate pH conditions for this energy cropping system.

Sweet potato (Ipomoea batatas L.) is a promising food and industrial crop that plays an important role in China’s agricultural poverty relief strategy. Selecting an appropriate cropping system for sweet-potato production could simultaneously achieve energy, economic, and environmental benefits. Therefore, the comprehensive assessment of diversified sweet-potato-based cropping systems (i.e., sweet potato monoculture (SP), continuous sweet potato cropping (SPSP), sweet potato–rice (SPRI), sweet potato–maize (SPMA), and sweet potato–potato (SPPO)) in South China was conducted with a field survey and life-cycle assessment. The data were collected quantitatively using a questionnaire for face-to-face interviewing of 70 farmers. The results indicated that the annual crop yield (sweet potato equivalent yield) of five cropping systems was in increasing order as SPPO > SPSP > SPMA > SPRI > SP. The SPMA system exhibited the highest net energy (499.09 GJ/ha) and energy rate (7.77). The SPSP system performed better in energy efficiency (0.90 kg/MJ), net return (140,284 CNY/ha), benefit to cost rate (3.20), and eco-efficiency (45 CNY/kg CO2-eq). The annual greenhouse-gas (GHG) emissions of five cropping systems ranked from lowest to highest as follows: SP < SPRI < SPSP < SPMA < SPPO. With comprehensive consideration, extended rotation systems (e.g., SPMA, SPRI, and SPSP) are proposed because they could effectively reduce GHG emissions while maintaining or even increasing the system’s productivity (ensuring food safety) in South China.

It is important to understand switchgrass (Panicum virgatum L.) productivity with relation to diverse nutrient deficiency conditions in order to optimize continuous biomass production in marginal lands. This study was conducted on a wasteland sandy soil (Aridosol) to assess biomass yield, nutrient uptake and nitrogen (N) recovery of switchgrass, and soil nitrate-N (NO3−-N) accumulation responses to N (120 kg N ha−1), phosphorus (P, 100 kg P2O5 ha−1), and potassium (K, 45 kg K2O ha−1) applications during 2015 and 2016 in Inner Mongolia, China. The experiment layout was a randomized complete block design with fertilizer mixture treatments of N, P, and K (NPK), P and K (PK), N and K (NK), N and P (NP), and a control with no fertilizer input (CK). Plant height and stem diameter remained unaffected by the different fertilizer treatments. Biomass yield with the NPK treatment in 2015 was 8.9 Mg ha−1 and in 2016 it was 7.3 Mg ha−1. In 2015, compared with the NPK treatment, a significant yield reduction of 33.7% was found with PK, 22.5% with NK, 28.1% with NP, and 40.5% with CK; however, in 2016, yield declined significantly only with CK compared to the rest of the fertilizer treatments, for which yields were statistically similar. Plant N content was reduced for the treatment PK (i.e. N omission); conversely, plant P and K content remained unaffected with P and K omission treatments. Plant nutrient uptake, particularly of N and K, was severely decreased by the nutrient omission treatments when averaged across 2 years. Apparent N recovery (ANR; quantity of N uptake per unit of N applied) was reduced for the NP and NK treatments, which led to an increase in soil NO3−-N accumulation in the top 0–20 cm layer, compared with the NPK treatment. However, ANR was the highest (37.2% in 2015) with the NPK treatment, which also reduced soil NO3−-N accumulation. A balanced N, P, and K fertilizer management approach is suggested to sustain switchgrass yield and stand persistence on semiarid, marginal, sandy wasteland.

An understanding of biomass yield and quality response to N supply is essential to breeding and cultivation of sorghum ( Sorghum bicolor (L.) Moench) for the production of bioethanol or forage. A two – year field experiment was conducted in 2013 and 2014 on semiarid marginal land in Inner Mongolia (39°10′N, 109°53′E) to determine the effects of N fertilizer rate (0, 60, 120, and 240 kg ha −1 ) on biomass yield and quality of sweet sorghum (GT-8) and biomass sorghum (GN-11), and on soil conditions. Results indicated that (1) biomass yield, leaf/stem ratio, and crude protein (CP), protein yield, theoretical ethanol yield (TEY), and soil net NO 3 − -N accumulation of both sorghum varieties in 2013 and 2014 significantly increased with the increasing N fertilizer rate from 0 to 240 kg ha −1 , whereas dry matter ratio and relative feed value (RFV) varied inversely with the N application rates. (2) Compared to biomass sorghum (GN-11), sweet sorghum (GT-8) demonstrated significant enhancement of forage quality components including CP, dry matter digestibility (DMD), dry matter intake (DMI), total digestible nutrients (TDN), net energy for lactation (NE L ), and RFV, with stems exhibiting higher forage quality than leaves. Biomass sorghum (GN-11) exhibited better performance for bioenergy production, with an average biomass yield of 7.9 t ha −1 and TEY of 3046.7 L ha −1 averaged across all N rates. (3) Annual average amount of net NO 3 − -N accumulation in 0–90 cm layers of two years significantly increased when fertilizer N exceeded 120 kg N ha −1 . In short, N fertilizer of 60 kg ha −1 is recommended to sweet sorghum for the forage production and 120 kg N ha −1 to biomass sorghum for bioenergy feedstock sustainability, respectively, meanwhile to prevent the soil degradation on semiarid marginal lands.

Plant density substantially affects sorghum (Sorghum bicolor (L.) Moench) productivity. Therefore, density optimisation plays a pivotal role in crop management practices. A 2-year field experiment was conducted on sandy loam marginal land in Ordos, Inner Mongolia, China, to (1) determine the mechanism underlying the impact of plant density (i.e. 6.0, 7.5, 9.0, 10.5 and 12.0 plant m−2) on biomass yield, quality and photosynthetic efficiency and (2) determine the optimum plant density for sweet sorghum variety GT-3 and biomass sorghum variety GN-4. Results indicate that plant height, leaf area index (LAI), leaf area duration (LAD) and biomass yield increased as plant density increased, but tiller number, stem diameter and net assimilation rate (NAR) decreased. The growth period between elongation and anthesis dates was crucial to sorghum productivity; during this period, LAD was the determining factor for biomass yield. Increase in plant density up to 10.5 plant m−2 led to a high LAI level, an extended LAD, a high and stable NAR and a positive balance between photosynthesis and respiration processes, all of which contributed to highest biomass yield (13.2 t ha−1). Ultimately, sweet-type variety GT-3 demonstrated the highest theoretical ethanol yield (4147 L ha−1) and relative feed value (112.3%) compared with biomass-type variety GN-4.