Biomass and energy yield of industrial hemp grown for biogas and solid fuel

This study examined the energy yield of hemp (Cannabis sativa L.) cultivated for energy purposes under cold climate conditions in Northern Europe. Split-plot field trials were carried out over three consecutive years to investigate different nitrogen fertilisation regimes. Dry matter yield per hectare, moisture content, hydrogen content and heating value were determined at roughly monthly intervals from July until the following spring every season. The energy yield was calculated and adjusted for a fair comparison with those of other energy crops commonly grown in the study region.Two harvest periods for optimal energy yield have been determined; harvest in September to October, when the hemp is used for biogas production, yielded 14.4 Mg ha⁻¹ and 296 GJ ha⁻¹; harvest in February to April, when the hemp is used as a solid fuel, yielded 9.9 Mg ha⁻¹ and 246 GJ ha⁻¹. For biogas production, the adjusted biomass energy yield of hemp was similar to that of maize and sugar beet and 24 and 14% greater than that of lucerne and clover-grass ley, respectively. As a solid fuel, the adjusted biomass energy yield of hemp was 120% higher than that of wheat straw and similar to that of reed canary grass. Annual variations in dry matter yield depending on weather conditions and sowing dates exceeded variations due to nitrogen fertilisation.Hemp is suitable as an energy crop in cold climate regions of Northern Europe, as it has similar or often higher energy yields than other common energy crops grown in these regions.     

Anaerobic digestion of industrial hemp-Effect of harvest time on methane energy yield per hectare

There is a worldwide emphasis to increase the share of renewable transportation fuels. When using agricultural land for production of renewable transportation fuels, the energy output per hectare for different crops and transportation fuels is a crucial factor. In this study, the gross methane energy yield per hectare from anaerobic digestion of industrial hemp (Cannabis sativa L.), was determined at four different harvest times between July and October in Southern Sweden, a cold climate region. The biomass yield was determined for three years and the methane yield was determined for two years through the biochemical methane potential test. The highest biomass yield, 16 tonnes dry matter per hectare on an average, and the highest methane energy yield per hectare was achieved when the hemp was harvested in September or October, with an average gross methane energy yield of 136 ± 24 GJ per hectare. There was no significant difference in the specific methane yield between the harvest times; the average being 234 ± 35 m³ per tonne volatile solids. Biogas from hemp turned out to be a high yielding alternative to the currently dominating renewable transportation fuels produced from crops grown in Sweden: ethanol from wheat and biodiesel from rapeseed.     

Harvest frequency effects on white clover forage biomass,quality, and theoretical ethanol yield

Understanding the growth of white clover (Trifolium repens L.) under varying management regimes and weather conditions will aid producers in making sound decisions on the utilization of this crop. The objectives of this study were to determine the effect of harvest frequencies on white clover forage biomass potential, theoretical ethanol yield, crude protein (CP) concentration, and in vitro digestible organic matter (IVDOM). Frequency of forage removal (treatment), year, and treatment × year interactions significantly affected forage quantity and quality. This 4-year study indicated that forage dry matter (DM) yield, theoretical ethanol yield, CP concentration, and IVDOM with four harvests (15 May, 1 and 15 June, and 1 July) or two harvests (15 May, and 15 June) were consistently better than the other one, two, or three harvest systems. Four harvests yielded on average 2380 ± 80 kg ha⁻¹ (a theoretical ethanol yield of 570 ± 20 L ha⁻¹) with 540 kg ha⁻¹ of CP and 1780 kg ha⁻¹ of digestible DM. Forage removed with two harvests (15 May and 15 June) yielded on average 2200 ± 80 kg ha⁻¹ (a theoretical ethanol yield of 530 ± 20 L ha⁻¹) with 490 kg ha⁻¹ of CP and 1640 kg ha⁻¹ of digestible DM. A two harvest system would reduce harvest costs over that of a four harvest system and would allow for two haying or grazing rotations (each with 28–30 day rest) before a decline of white clover DM production in mid-summer.     

Firewood yield and profitability of a traditional Daniellia oliveri short-rotation coppice on fallow lands in Benin

Sub-Saharan Africa has a great diversity of local coppicing species which are exploited in traditional short coppice systems for firewood. Biomass yield and profitability of these systems as well as their responses to silvicultural improvement are little known. This study evaluated the firewood yield and the profitability of a traditional Daniellia oliveri short-rotation coppice on fallow lands in central Benin. Two weed management options were considered: (1) the weedy option, usually practiced by locals, which experienced grass competition and bushfires, and (2) the weed-free option, which consisted in periodic removal of grasses and other species. Destructive measurements and allometric equations were used to estimate biomass yield in 12 plots over 42 months. A cost-benefit analysis model based on the net present value and the benefit-cost ratio was used to compare the profitability of the two management options. Biomass accumulation rate averaged 1.08 ± 0.20 tonnes of dry matter ha⁻¹ year⁻¹ (t DM ha⁻¹ year⁻¹) in weedy conditions. Weed removal improved 3.5 times this rate in weed-free plots (3.83 ± 0.47 t DM ha⁻¹ year⁻¹). After 42 months, total biomass reached 3.67 ± 0.65 t DM ha⁻¹ in weedy plots and 11.63 ± 0.76 t DM ha⁻¹ in weed-free plots. Most of the biomass (≥88%) was marketable in local markets. Coppice exploitation was profitable after 24 months for both management options. Weed removal improved the profits three times. A sensitivity analysis showed that both options were still profitable with up to 25% increase of labour and transport costs, 25% decrease of biomass price and 12% increase of the discount rate.     

Evaluation of methane production from maize silage by harvest of different plant portions

Biogas production is mainly based on the anaerobic digestion of cereals silages and maize silage is the most utilized. Regarding biogas production, the most important portion of the plant is the ear. The corn ear, due to high starch content, is characterized by a higher biogas production compared to the silage of the whole plant.In this paper, we present the results of experimental field tests carried out in Northern Italy that aim to evaluate the anaerobic methane potential (BMP) of different portions of ensiled maize hybrids. The BMP production is evaluated considering the possibility of harvesting and ensiling: the whole plant; the plant cut at 75 cm of height; the ear only; the plant without the ear. For the different solutions, the results are reported as specific BMP and as average biogas production achievable per hectare. The methane production by harvesting and ensiling the whole plant (10,212 and 10,605 m³ ha⁻¹, for maize class 600 and 700, respectively) is higher than the ones achievable by the other plant portions (7961 and 7707 m³ ha⁻¹, from the ear; 9523 and 9784 m³ ha⁻¹, from the plant cut at 75 cm; 3328 and 3554 m³ ha⁻¹, from the plant without the ear, for maize class 600 and 700, respectively). The harvest of the whole plant, although it is the most productive solution, could not be the best solution under an economic and environmental point of view. Harvesting only the ear can be interesting considering the new Italian subsidy framework and for the biogas plants fed by biomass transported over long distances.     

Sustainable use of eucalypt biomass grown on short rotation coppice for bioenergy

Bioenergy is one of the alternatives to reduce the dependence of global energy on fossil fuels. The short rotation coppice (SRC) of eucalypt species appears as an interesting option for forest biomass production in a short time. However, the harvesting of whole trees (included the crown) in SRC systems has implications on sustainable land use. More information is required on the increase of biomass as renewable energy resource to achieve the sustainability of these crops. The main objective of this research was to evaluate the sustainable use of biomass from very high-density eucalypt plantations, managed at tropical conditions for bioenergy. To accomplish this objective, the tree was fractionated into three fractions: stem, branches, and leaves, and there was determination of the dry matter, energy yield, and nutrients export. This experiment used a short rotation coppice, a hybrid clone of Eucalyptus urophylla × Eucalyptus grandis, of 2 years old. According to the results obtained, the density planting and fertilization levels have a greater influence on the dry matter yield, energy yield, and nutrient exports. The higher density planting reaches mean values of 30.9 tonnes of dry matter per hectare (t DM ha⁻¹) and 743.3 GJ ha⁻¹. Considering the biomass yield and nutrients export of short rotation coppice of eucalypt, the higher density planting with the lower dose of fertilization is more indicative of sustainable use. The leaves have an important participation in nutrients export and should be retained in the soil of forest.     

Biomass estimates,characteristics, biochemical methane potential,kinetics and energy flow from Jatropha curcus on dry lands

In this study, we examined the production of Jatropha curcus plants on 1 ha of rain fed dry lands. All of the plant components that would result from plantation tending, fruit harvesting and processing were sampled for their yield and chemical composition, and then subjected to the biochemical methane potential (BMP) assay. The component parts exhibited significant variation in BMP which was reflected in their ultimate methane yield which ranged from 0.08 to 0.97 L g^?1 VS added, and their first order kinetics which ranged from 0.07 to 0.14 d^?1. We examined two integrated utilization schemes: the first which converted plant prunings, fruit hulls and de-oiled seed cake to methane, and the oil to fatty acid methyl-ester (FAME); the second was to convert the seeds, plant prunings and fruit hulls entirely to methane. The basis for the plantation was, a density of 4444 plant ha^?1 (1.5 m × 1.5 m spacing), with a seed yield of 0.911 kg TS plant^?1 (1 kg total weight) with an oil content of 35% providing an annual oil yield of 1.42 t y^?1. The corresponding yields of pruned leaves, fruit hulls and de-oiled cake are 0.97, 1.0, and 2.35 t VS ha y^?1, respectively. An integrated scheme of producing biogas by means of anaerobic digestion of the latter components and oil for biodiesel would produce 90 GJ ha^?1 y^?1 in total with the oil being 54 GJ. The alternative biogas only option which would convert the seed oil into methane instead of biodiesel would produce 97 GJ ha^?1 y^?1.     

Vegetable oil production potential from Jatropha curcas, Croton megalocarpus, Aleurites moluccana, Moringa oleifera and Pachira glabra: Assessment of renewable energy resources for bio-energy production in Africa

Research on vegetable oil for biofuels in Africa and Asia has focused mainly on Jatropha curcas while other potential oil bearing plants have received little attention. Vegetable oil production potential for five oil bearing plant species namely: Aleurites moluccana, Croton megalocarpus, Jatropha curcas, Moringa oleifera and Pachira glabra were investigated. Nuts and seeds of the plants were collected from the wild and their potential for vegetable oil production assessed in terms of seed/nut acreage yield, seed/nut oil content, harvesting requirement, and upstream processing before vegetable oil recovery. All five varieties were found to contain acceptable but different oil content ranging from 20 to 33% w/w, and seed/nut acreage yield of 3 t ha⁻¹ y⁻¹ to 12.5 t ha⁻¹ y⁻¹. Upstream processing was needed for A. moluccana to break open nuts to release the kernel, and dehulling for both C. megalocarpus and J. curcas to release the seeds, before extracting the vegetable oil, while the seeds of both M. oleifera and P. glabra did not need upstream processing. The Multi-criteria Decision Analysis ranked C. megalocarpus as the plant with the highest vegetable oil production potential of 1.8 t ha⁻¹ y⁻¹ followed by M. oleifera, J. curcas (1 t ha⁻¹ y⁻¹), A. moluccana, and P. glabra. The analysis underlines the need for more studies on C. megalocarpus and M. oleifera for biofuel production in Africa and other regions.     

Yield comparison of four lignocellulosic perennial energy crop species

From 2006 to 2009, block template experiments were conducted to evaluate the biomass yield of four crop species—Amur silvergrass, Giant Miscanthus, Virginia fanpetals, and two Basket willow clones—at the University of Life Science, Lublin, Poland. The dry matter (d m) yields and number of shoots were determined each November, while biomass moisture levels were determined every November and March. The averages of the 4-year research datasets indicated that Giant Miscanthus produced the greatest biomass (16.5 t ha⁻¹ d m), while the two Basket willow clones (8.8–10.2) t ha⁻¹ d m, and Amur silvergrass (6.2 t ha⁻¹ d m) produced the lowest biomass. The mean yield of Virginia fanpetals was 13.0 t ha⁻¹ d m. The largest number of shoots per one m² were produced by Miscanthus species (55 units), with Basket willow and Virginia fanpetals producing half this amount (24–28 units). Similar moisture levels were obtained for Basket willow biomass harvested in autumn (49.5–54.6)% and winter (48.4–49.7)%. The biomass moisture levels of the other species in March was approximately two times lower (14–29)% than that in November (27–70)%.In a second experiment, the effect of varying plant density (10 000 and 30 000 plants per ha) on the yield of Giant Miscanthus was investigated. Double the biomass yield was obtained in crops with a density of 30 000 plants per hectare compared to 10 thousand. The higher yields were accompanied by larger, heavier, taller, but thinner shoots.     

Energy recovery from grass of urban roadside verges by anaerobic digestion and combustion after pre-processing

Grass from urban roadside verges is a potential, though widely unused, resource for bioenergy recovery. Two possible bioenergy recovery techniques were tested, i.e. i) direct anaerobic digestion of the whole parent material and ii) the “integrated generation of solid fuel and biogas from biomass” (IFBB) procedure, which divides biomass into a press fluid and a press cake by mashing and mechanical dewatering. Biomass yield, chemical composition and canopy height of biomass, contribution of functional groups, fermentation characteristics of silage and press fluids, as well as characteristics of the produced solid fuel was investigated, applying a 4-cut management for anaerobic digestion, a 2-cut management for IFBB and an 8 times mulching as a reference. Mean annual biomass yield (2013 and 2014) was 3.24, 3.33 and 5.68 t dry matter ha⁻¹ for the mulching, 4-cut management and 2-cut management, respectively. Yields were higher in 2014 due to more favourable weather conditions. Fibre concentration was higher in material of the 2-cut management than in the 4-cut management, however, methane yield of the corresponding silages was the same. Highest methane yield was gained from press fluids with 292 l_N kg⁻¹ volatile solids. The press cake had a lower heating value of 16 MJ kg⁻¹ dry matter and a K₂O/CaO index of 0.51–0.88. Gross energy output was 26.4 GJ ha⁻¹ for anaerobic digestion and 84.4 GJ ha⁻¹ for IFBB. Thus, an altered roadside verge management with reduced cutting frequency might allow a significant energy recovery and improved ecosystem services, i.e. increased biodiversity.     

Determination of biomass accumulation in mixed belts of Salix,Corylus and Alnus species in combined food and energy production system

Given the energetic, demographic and the climatic challenges faced today, we designed a combined food and energy (CFE) production system integrating food, fodder and mixed belts of Salix, Alnus and Corylus sp. as bioenergy belts. The objective was to assess the shoot dry weight-stem diameter allometric relationship based on stem diameter at 10 (SD₁₀) and 55 cm (SD₅₅) from the shoot base in the mixed bioenergy belts. Allometric relations based on SD₁₀ and SD₅₅ explained 90–96% and 90–98% of the variation in shoot dry weights respectively with no differences between the destructive and the non-destructive methods. The individual stool yields varied widely among the species and within willow species with biomass yield range of 37.60–92.00 oven dry tons (ODT) ha⁻¹ in 4-year growth cycle. The biomass yield of the bioenergy belt, predicted by allometric relations was 48.84 ODT ha⁻¹ in 4-year growth cycle corresponding to 12.21 ODT ha⁻¹ year⁻¹. The relatively high biomass yield is attributed to the border effects and the ‘fertilizing effect’ of alder due to nitrogen fixation, benefitting other SWRC components. On termination of 4-year growth cycle, the bioenergy belts were harvested and the biomass yield recorded was 12.54 ODT ha⁻¹ year⁻¹, in close proximity to the biomass yield predicted by the allometric equations, lending confidence and robustness of the model for biomass yield determination in such integrated agro-ecosystem.     

Biomass equations for determining fractions of common and grey alders growing on abandoned farmland and some practical implications

A study was conducted in order to construct functions for above-ground biomass of fractions of young common alders (Alnus glutinosa (L.) Gaertn.) and grey alders (Alnus incana (L.) Moench.). The constructed functions were designed to be used to predict the amount of biofuel produced from small areas. Biomass production was estimated in 10 stands of common alder and 15 stands of grey alder, growing on abandoned farmland. The common alder stands were located in Sweden at latitudes ranging from 58° to 60° N, and their total age varied from 4 to 36 years. Grey alder stands were located at latitudes ranging from 60° to 66° N, and their total age varied from 5 to 35 years. A modified ‘mean tree technique’ was used to estimate biomass production, i.e. the tallest tree was chosen for sampling. The mean total dry weight above the stump level for common alder stands was 39 tonnes ha⁻¹ with a range of 5 to 140 d.w. ha⁻¹ and 61 tonnes ha⁻¹ with a range of 3 to 140 tonnes d.w. ha⁻¹ for grey alder stands. The mean annual increment for common alder stands was 3.11 tonnes ha⁻¹ y⁻¹ (0.50–7.71) and 4.38 tonnes ha⁻¹ y⁻¹ (0.66–9.32) for grey alder stands. In addition to estimating conventional dry weights of trees and tree components, specific leaf area, total surface area and leaf area index (LAI), among other measures, were estimated. The mean LAI for common alder stands was 3.16 and 2.03 for grey alder stands. The specific leaf area per tree for common alder was 16.1 m² kg⁻¹ and 14.4 m² kg⁻¹ for grey alder. Practical implications of the findings are discussed.     

Prospects of whole grain crops of wheat,rye and triticale under different fertilizer regimes for energy production

Cereal grain yield and biomass production are affected by fertilizer application strategies. In order to quantify the performance of wheat, rye and triticale cultivars for use as energy crops, field experiments with either modified phosphorus–potassium or potassium applications were designed at two locations in Denmark over a 3-year period. Five wheat cultivars (‘Astron’, ‘Herzog’, ‘Kosack’, ‘Kraka’ and ‘Ure’), two winter rye cultivars (the population cultivar ‘Motto’ and the hybrid cultivar ‘Marder’) and the triticale cultivar ‘Alamo’ were selected. The grain and straw fractions were analysed for biomass, ash and contents of nitrogen (N), K, Cl, sulphur (S) and Na.Dry matter yields varied between 11.5 and 15.9 t ha⁻¹ at the two locations. Triticale and rye had a higher total dry matter yield than wheat, even at lower inputs of N fertilizer. Thus, the constant high yield of rye and triticale is an advantage for biomass for energy purposes. The mineral content of the grain fraction changed only little between years and locations. By contrast, large variations in the analysed ions in the straw fraction between years and locations were observed. The use of K fertilizers resulted in a significantly increased concentration of K in the straw. However, this increased concentration was eliminated in years with high precipitation in the final 3 weeks before harvest, where substantial amounts of K, Cl and S were removed. The results are discussed in relation to the possible use of grain crops for energy production.     

Growth,yield, fiber content and lodging resistance in eight varieties of Cenchrus purpureus (Schumach.) Morrone intended as energy crop

Growth, biomass yield, fiber content and lodging resistance were studied, during a six month growth period, for eight varieties of Cenchrus purpureus, intended as energy crop, in Veracruz, Mexico. Then, only yield at day 182 was assessed for two additional years. The varieties were: CT115 (CT), African Cane (AC), Taiwan (TAI), King Grass (KG), Vruckwona (VRU), Roxo (RX), OM22 (OM) and Cameroon (CAM). Local weather is warm and sub-humid, historical data for monthly average temperature and annual rainfall were 25.8 °C and 1142 mm, respectively. Height, diameter and light interception were measured monthly from day 65–185. At day 185, biomass yield and tiller density were measured. Number of lying tillers was counted to estimate lodging resistance. Cellulose and hemicellulose content were estimated in leaf and stem. No differences were found for dry matter yield or stem yield at day 185 in the first year. Regarding the next two years, TAI yielded above CT, OM or ROX. Average dry matter yield was higher in the second year than in the establishment cycle (38.6 vs 21.1 Mg ha⁻¹), but decreased in the third year (32.2 Mg ha⁻¹). In both stem and whole plant, AC and KG showed higher hemicellulose content than RX, OM or CT; while AC and VRU had higher cellulose than RX in stem, or than CT in the whole plant. Furthermore, varieties AC, KG, VRU and TAI were resistant to lodging and had a higher fiber content, so they are recommended as energetic crops.     

The impact of sugar beet varieties and cultivation conditions on ethanol productivity

The 49 hybrids of sugar beet and semi-forage beet used in this research were characterized by a variable concentration of saccharose (14.58% ± 1.28), Na (5.51 ± 3.07 mmol kg⁻¹), K (57.44 ± 9.71 mmol kg⁻¹), N (21.68 ± 4.75 mmol kg⁻¹), yield (68.36 ± 10.29 t ha⁻¹) and differentiated fermentation efficiency (5.14 ± 1.22 m³ ha⁻¹).It was found that the effectiveness of fermentation depends not only on the saccharose content in the sugar beet, but also its relationships with other components of the dry matter. High sugar beet yield have significant effect on ethanol yield. The impurities such as K, N and Na have a negative effect on efficiency of the fermentation process. It also specifies varietal differences on ethanol yield. It has been found that high ethanol yield is correlated with diploid hybrids which are sugar hybrids.     

Utilization of summer legumes as bioenergy feedstocks

Sunn hemp (Crotolaria juncea), is a fast growing, high biomass yielding tropical legume that may be a possible southeastern bioenergy crop. When comparing this legume to a commonly grown summer legume – cowpeas (Vigna unguiculata), sunn hemp was superior in biomass yield (kg ha^?1) and subsequent energy yield (GJ ha^?1). In one year of the study after 12 weeks of growth, sunn hemp had 10.7 Mg ha^?1 of biomass with an energy content of 19.0 Mg ha^?1. This resulted in an energy yield of 204 GJ ha^?1. The energy content was 6% greater than that of cowpeas. Eventhough sunn hemp had a greater amount of ash, plant mineral concentrations were lower in some cases of minerals (K, Ca, Mg, S) known to reduce thermochemical conversion process efficiency. Pyrolytic degradation of both legumes revealed that sunn hemp began to degrade at higher temperatures as well as release greater amounts of volatile matter at a faster rate.     

Influence of climate parameters and management of permanent grassland on biogas yield and GHG emission substitution potential

In many regions of Europe, grassland is no longer needed for fodder production as it is not economically viable. However, due to the important role it plays in soil carbon storage, it is imperative that grassland should be maintained. The energetic use of its biomass could be an alternative means of generating income from grassland.The aim of this study is to identify the best permanent grasslands management systems for CHP production with regard to maximizing biogas yields, energy use efficiency and greenhouse gas mitigation potential.A long-term field trial was established in 1994 and managed under various nitrogen fertilizer level regimes and cutting frequencies until 2007. Annual dry matter yields ranged between 9.1 t ha⁻¹ and 10.8 t ha⁻¹.Based on these data the methane yields for the different cutting regimes were calculated. The highest methane yield of 288.4 L kg⁻¹ oDM was calculated for a yearly cutting regime of four cuts.Energy and CO₂ balances were calculated to assess the energy efficiency and the global-warming potential of power generation in a CHP plant using biogas produced from the different grassland management systems. The highest net energy yield (48.52 GJ per hectare per year) was calculated for a two-cut regime. Furthermore, the highest CO₂ equivalent reduction potential was also documented for a cutting frequency of two cuts per year. In this case a CO_2eq mass reduction of 5.1 t per hectare per year could be achieved compared to fossil fuel (consisting of a German power mix and natural gas components) reference systems.     

Impact of different establishment methods in terms of tillage and weed management systems on biomass production of willow grown as short rotation coppice

To date little information is available on methods including soil preparation and weed control in SRC. For this purpose, in 2010, a field trial with willow cv. ‘Tordis’ was established in southwest Germany. Three different tillage systems (mouldboard plough, chisel plough + ley crop, no-till) were implemented in the establishment year in combination with eight chemical and mechanical weed management systems. Over a period of three years, plant and weed specific parameters were collected to determine the effect of tillage systems and weed treatments on final biomass production of willow. The highest biomass yields were obtained by mouldboard plough with chemical weed control (14.0 Mg ha⁻¹ dry matter) as well as by mouldboard plough with rotivation and band spraying of herbicides (14.2 Mg ha⁻¹ dry matter), followed by 13.7 Mg ha⁻¹ dry matter in no-till with broadcast application of herbicides. Chisel ploughing with ley crop led to lower willow yields in most weed treatments. It was assumed that chisel ploughing + ley crop would lead to a high competition for light, water and nutrients especially in the first year. Consequently, it is not recommended as an establishment method for willow. Additionally, mulching with wood chips and no weed management generally resulted in low biomass yields. Overall, the results suggest that the tillage system in combination with effective chemical or mechanical weed control is of major importance for the success of willow establishment.     

Effects of delayed winter harvest on biomass yield and quality of napiergrass and energycane

Napiergrass (Cenchrus purpureus (Schumach.) Morrone) and energycane (Saccharum hyb.) are perennial grasses that are well-suited for biomass production in the southeastern USA. The purpose of this study was to determine the effects of delayed winter harvest on biomass yield and quality of these grasses. The study was conducted on two adjacent sites near Midville, GA. Each site used a split-plot design with four replications, with species as the main plot, and harvest times (December, January, or February) as sub-plots. Dry matter (DM) yields were measured by mechanical harvesting, and a sample of biomass was taken from each harvest for determination of ethanol production by simultaneous saccharification and fermentation (SSF). Biomass moisture, N, P, K, and ash mass fractions were also measured. Energycane DM yields were stable from December (46.8 Mg ha⁻¹) to January (42.9 Mg ha⁻¹), but then declined (36.8 Mg ha⁻¹), while napiergrass yields declined sharply from December (47.0 Mg ha⁻¹) to January (35.0 Mg ha⁻¹). Napiergrass moisture mass fraction was reduced by an average of 18% in February harvests compared to December. Mass fractions of N, K, and ash tended to decrease with later harvesting, but sometimes increased due to changes in biomass composition. Delaying harvest of napiergrass from December to January reduced N removal by an average of 144 kg ha⁻¹, while delaying harvest of energycane to February reduced N removal by an average of 54 kg ha⁻¹. In SSF, later-harvested energycane produced less ethanol per unit of DM while napiergrass was less affected by harvest date.     

Yield,water use efficiency and economic analysis of energy sorghum in South Texas

Yields, water use efficiency and economic returns (net farm revenues) of biomass sorghum [Sorghum bicolor (L.) Moench] were investigated over two years (2012 and 2014) under limited water resource conditions. Energy sorghum was grown under four water supply regimes: rain-fed (or dry-land, level 1), 50% (level 2), 75% (level 3) and 100% (level 4) of crop evapotranspiration rates (% ET_c). Biomass yields ranged from 5.8 to 16.6 Mg ha⁻¹ (dry weight) after 126 days of growth. Average water use efficiencies ranged from 3.95 kg m⁻³ to 23.4 kg m⁻³. Net return was approximately 410 $ ha⁻¹ with water depths above 400 ha-mm. These results suggest that it is possible to obtain more than 60 Mg ha⁻¹ of sorghum biomass (wet basis) with at least 425 mm of water. While biomass yield under irrigation was greater than rain-fed conditions, there were no significant differences among irrigation treatments. Biomass chemical composition did not differ significantly among water treatments suggesting that biofuel quality would not be affected by water deficits.