Bioenergy Crops

Sewage sludge is rich in essential plant nutrients, but its use is restricted for crop production due to the pollutants it contains, such as metalloids and heavy metals. Sludge is also very sticky and compact. Therefore, the objectives of this work were to evaluate (1) the impact of various amounts of sludge on bioenergy crop productivity and quality and (2) the use of peat as an adjuvant to reduce the stickiness, density and nutrient richness of the sludge. Three different applications of sludge were examined, high, low (50% of high) and low mixed with an equal volume of peat. The sludge–peat mix increased significantly leaf area and biomass accumulation of maize and hemp. High sludge and sludge–peat mix applications increased significantly the leaf area and biomass accumulation as well as the net photosynthesis of oilseed rape. High sludge application resulted in the highest heavy metal and metalloid accumulation in maize and hemp. Sludge–peat mix resulted in the highest heavy metal and metalloid accumulation in oilseed rape. However, the sludge–peat mix application provided the best feedstock quality in all three crops, since chloride, silicon and sulfur concentrations and ash content in plant material were the lowest of the three sludge treatments.

In this paper, an agent-based model of heterogeneous farmer decision-making was coupled with an individual-based model of skylark breeding populations, and applied to a small intensive arable catchment in Scotland. The impacts of farmer decisions on a tradeoff between food and bioenergy production, and skylark numbers, were simulated under the assumptions of three socioeconomic scenarios until the year 2050. Bioenergy and food production had a significant negative effect on adult and fledgling skylarks. In a business-as-usual context, the production of food and bioenergy increases smoothly, and the number of skylarks is more stable over time than in other scenarios. Food production was higher in an economic liberalisation scenario, due to intensive management and higher yield performance. This explained the low average number of skylarks found at the landscape level in this scenario. The number of skylarks was highest in a sustainability-oriented scenario, but a sharp decrease was observed from 2035 onwards due to the large area planted with bioenergy crops. The different values for economic, environmental and social attributes of farmer decisions played an important role in the land use mosaic, the implementation of ecologically-related actions and on the provision of ecosystem services and biodiversity. Overall, results suggest that a re-assessment of policy targets and design is necessary to maximise environmental management efficiency at the catchment level by taking into account the heterogeneity in farmer objectives and the tradeoffs in ecosystem services provision. The novel approach of coupling an ABM with an IBM is encouraged in further land use related studies.

The US Department of Energy conducted two studies to estimate the potential of cellulosic biomass crops for production of biofuels on a national scale. However, limited long-term experimental information is available to support the resultant yield projections. The objectives of this research were: (i) to determine long-term (>10 years) biomass yields and soil impacts of switchgrass (Panicum vir-gatum L.), giant reed (Arundo donax L.) and mimosa (Albizia julibrissin Durazz.) in Alabama; and (ii) to establish relationships between precipitation and yields of these perennial biomass crops, and yields of cotton, maize, and soybean. Mimosa and giant reed received no fertilizer and were harvested once each year while switchgrass received 84 kg ha –1 of N fertilizer annually, and was harvested twice each year. Cotton, maize, and soybean were managed according to traditional practices for these crops in this region. Average annual biomass yields of mimosa, giant reed, and switchgrass were 40.1, 35.5 and 23.5 kg ha –1 over 16-, 11-and 22-year periods, respectively, with corresponding estimated annual N accumulation in aboveground biomass of 388, 372 and 163 kg ha –1. Yields of maize, cotton and soybean decreased sharply with decreasing precipitation, but there was no corresponding decrease in yield of the three perennial biomass crops. Changes in the yields of the biomass crops with age were also relatively small. Analysis of topsoil samples suggested considerably less removal of P, K, Ca, and Mg than was estimated from yield and concentrations of these elements in the biomass that was actually removed.

Recycling nutrients saves energy and improves agricultural sustainability. Sewage sludge contains 2.6% P and 3.1% N, so the availability of these nutrients was investigated using four crops grown in either soil or sand. Further attention was paid to the role of mycorrhiza in improvement of nutrient availability. The content of heavy metals and metalloids in the feedstock was analyzed. Sewage sludge application resulted in greater biomass accumulation in ryegrass than comparable single applications of either synthetic fertilizer or digested sludge. Sewage sludge application resulted in more numerous mycorrhizal spores in soil and increased root colonization in comparison to synthetic fertilizer. All plants studied had mycorrhizal colonized roots, with the highest colonization rate in maize, followed by hemp. Sewage sludge application resulted in the highest P uptake in all soil-grown plants. In conclusion, sewage sludge application increased feedstock yield, provided beneficial use for organic wastes, and contributed to the sustainability of bioenergy feedstock production systems. It also improves the soil conditions and plant nutrition through colonization by mycorrhizal fungi as well as reducing leaching and need of synthetic fertilizers.

The cold tolerance of winter-dormant rhizomes was evaluated in diploid, allotriploid, and allotetraploid hybrids of Miscanthus sinensis and Miscanthus sacchariflorus grown in a field setting. Two artificial freezing protocols were tested: one lowered the temperature continuously by 1°C h(-1) to the treatment temperature and another lowered the temperature in stages of 24h each to the treatment temperature. Electrolyte leakage and rhizome sprouting assays after the cold treatment assessed plant and tissue viability. Results from the continuous-cooling trial showed that Miscanthus rhizomes from all genotypes tolerated temperatures as low as -6.5 °C; however, the slower, staged-cooling procedure enabled rhizomes from two diploid lines to survive temperatures as low as -14 °C. Allopolyploid genotypes showed no change in the lethal temperature threshold between the continuous and staged-cooling procedure, indicating that they have little ability to acclimate to subzero temperatures. The ...

The purpose of this study was to assess the changes in switchgrass
(Panicum virgatum L.) biomass quality as affected by N rate, harvest
time, and storage. This research was conducted near Bristol,
SD, in 2010 and 2011. Treatments included three N rates (0, 56,
and 112 kg N ha–1) applied annually and each N rate replicated
four times. After a killing frost, all of the plots were harvested and
baled in large round bales in October 2010 and November 2011.
An area of about 30 m2 from each plot was left unharvested to
represent storage of standing switchgrass over the winter and to
determine dry matter yields. Switchgrass was analyzed for hemicellulose,
cellulose, lignin, mineral elements, N, and C. In the
first season, storage of the fall harvested switchgrass bales numerically
increased the concentrations of hemicellulose, lignin, and
N. In the second season, they increased significantly. Mineral
elements significantly increased in both sampling seasons. Delaying
harvest until spring decreased lignin, N, and mineral elements
concentration, and increased cellulose and hemicellulose
concentrations, but also reduced biomass yield. Results from this
study suggest that delaying the switchgrass harvest until spring
increased the overall feedstock quality for ethanol production,
but yield reductions must be considered to determine the overall
economic impact of a delayed harvest.

Utilization of sludge is an attractive option for fertilizing bioenergy crops, since in addition to its valuable macro- and micro-nutrients, it may also contains some pollutants. Therefore, a three-year field experiment was conducted to investigate the suitability of sewage and digested sludge in comparison to synthetic fertilizer on biomass production and its quality in three crop species, with specific attention to the relationship between N availability and biomass accumulation. Fertilizer treatments for each crop species were standardized on the basis of total Nitrogen as follows: maize 120 kg ha−1, fibre hemp 60 kg ha−1 and oilseed rape 90 kg ha−1 Nitrogen. The highest biomass yield of maize (30 Mg ha−1 Dry Mass) and hemp (15 Mg ha−1 Dry Mass) was obtained from the sewage sludge treatment. The sludge treatment also gave the highest leaf Nitrogen mass in biomass of both maize (14 g kg−1) and hemp (18 g kg−1) at 60 DAS (flowering stage). Sewage sludge increased slightly gross energy yield of maize (438 GJ ha−1) and hemp (272 GJ ha−1) in comparison to other treatments. The mass fraction of ash and the combustion-relevant elements such as Chlorine, Potassium, Sodium and Calcium were lower in crops fertilized with sewage sludge than in those fertilized with synthetic fertilizer. In conclusion, sewage sludge produced as high biomass yield as synthetic fertilizers. In addition, it improved growth and quality of biomass.