Yield and Nutrient Removal by Bioenergy Grasses on Swine Effluent Spray Fields in the Coastal Plain Region of North Carolina

Bioenergy grasses such as giant miscanthus (Miscanthus × giganteus) and switchgrass (Panicum virgatum L.) are promising alternatives to the traditional coastal bermudagrass [Cynodon dactylon (L.) Pers.] at spray fields in Eastern North Carolina. The objective of this study was to determine the impact of different harvest practices on yield and nutrient removal of miscanthus and switchgrass in a swine (Sus scrofa domesticus) lagoon effluent spray field environment. Field trials of grasses under six single-cut and double-cut harvest practices (May/October, June/October, July/October, Aug/October, October only, and December only) were established at three commercial swine farms in Eastern North Carolina in either 2011 or 2012. Throughout the 4-year experimental period (2012–2015), both miscanthus and switchgrass produced significantly higher biomass yield than coastal bermudagrass. Two-cut harvest systems significantly improved the yields of miscanthus and switchgrass relative to a single harvest in December at spray fields. The maximum yields were 24 Mg ha^?1 year^?1 for miscanthus and 18 Mg ha^?1 year^?1 for switchgrass. Bioenergy grasses removed more nutrients under two-cut systems than under a single harvest. The significantly greater nutrient removals under two-cut harvest systems would result in lower requirements for receiver crop acreage and are more desirable from a spray field nutrient management perspective.     

Yield and Nitrogen Removal of Bioenergy Grasses as Influenced by Nitrogen Rate and Harvest Management in the Coastal Plain Region of North Carolina

The agronomic performances of giant miscanthus (Miscanthus x giganteus) and switchgrass (Panicum virgatum L.) grown as bioenergy grasses are still unclear in North Carolina, due to a relatively short period of introduction. The objectives of the study were to compare the biomass yield and annual N removal of perennial bioenergy grasses and the commonly grown coastal bermudagrass [Cynodon dactylon (L.) Pers.], and to determine the optimum N rates and harvest practices for switchgrass and miscanthus. A 4-year field trial of the grasses under five annual harvest frequencies (May/Oct, June/Oct, July/Oct, Aug/Oct, and October only) and five annual N rates (0, 67,134, 202, and 268 kg N ha^?1) was established at a research farm in Eastern North Carolina in 2011. Across harvest treatments and N rates, greatest biomass was achieved in the second growth year for both miscanthus (19.0 Mg ha^?1) and switchgrass (15.9 Mg ha^?1). Grasses demonstrated no N response until the second or the third year after crop establishment. Miscanthus reached a yield plateau with a N rate of 134 kg ha^?1 since achieving plant maturity in 2013, whereas switchgrass demonstrated an increasing fertilizer N response from 134 kg N ha^?1 in the third growth year (2014) to 268 kg N ha^?1 in the fourth growth year (2015). The two-cut harvest system is not recommended for bioenergy biomass production in this region because it does not improve biomass yield and increased N removal leads to additional costs.     

Niche-based assessment of contributions of legumes to the nitrogen economy of Western Kenya smallholder farms

Nitrogen (N) deficiency is a major constraint to the productivity of the African smallholder farming systems. Grain, green manure and forage legumes have the potential to improve the soil N fertility of smallholder farming systems through biological N₂-fixation. The N₂-fixation of bean (Phaseolus vulgaris), soyabean (Glycine max), groundnut (Arachis hypogaea), Lima bean (Phaseolus lunatus), lablab (Lablab purpureus), velvet bean (Mucuna pruriens), crotalaria (Crotalaria ochroleuca), jackbean (Canavalia ensiformis), desmodium (Desmodium uncinatum), stylo (Stylosanthes guianensis) and siratro (Macroptilium atropurpureum) was assessed using the ¹⁵N natural abundance method. The experiments were conducted at three sites in western Kenya, selected on an agro-ecological zone (AEZ) gradient defined by rainfall. On a relative scale, Museno represents high potential AEZ 1, Majengo medium potential AEZ 2 and Ndori low potential AEZ 3. Rainfall in the year of experimentation was highest in AEZ 2, followed by AEZ 1 and AEZ 3. Experimental fields were classified into high, medium and low fertility classes, to assess the influence of soil fertility on N₂-fixation performance. The legumes were planted with triple super phosphate (TSP) at 30 kg P ha^?1, with an extra soyabean plot planted without TSP (soyabean-P), to assess response to P, and no artificial inoculation was done. Legume grain yield, shoot N accumulation, %N derived from N₂-fixation, N₂-fixation and net N inputs differed significantly (P<0.01) with rainfall and soil fertility. Mean grain yield ranged from 0.86 Mg ha^?1, in AEZ 2, to 0.30 Mg ha^?1, in AEZ 3, and from 0.78 Mg ha^?1, in the high fertility field, to 0.48 Mg ha^?1, in the low fertility field. Shoot N accumulation ranged from a maximum of 486 kg N ha^?1 in AEZ 2, to a minimum of 10 kg N ha^?1 in AEZ 3. Based on shoot biomass estimates, the species fixed 25–90% of their N requirements in AEZ 2, 23–90% in AEZ 1, and 7–77% in AEZ 3. Mean N₂-fixation by green manure legumes ranged from 319 kg ha^?1 (velvet bean) in AEZ 2 to 29 kg ha^?1 (jackbean) in AEZ 3. For the forage legumes, mean N₂-fixation ranged from 97 kg N ha^?1 for desmodium in AEZ 2 to 39 kg N ha^?1 for siratro in AEZ 3, while for the grain legumes, the range was from 172 kg N ha^?1 for lablab in AEZ 1 to 3 kg N ha^?1 for soyabean-P in AEZ 3. Lablab and groundnut showed consistently greater N₂-fixation and net N inputs across agro-ecological and soil fertility gradients. The use of maize as reference crop resulted in lower N₂-fixation values than when broad-leaved weed plants were used. The results demonstrate differential contributions of the green manure, forage and grain legume species to soil fertility improvement in different biophysical niches in smallholder farming systems and suggest that appropriate selection is needed to match species with the niches and farmers’ needs.     

Effect of Nitrogen Fertilization and Residual Nitrogen on Biomass Yield of Switchgrass

Switchgrass, Panicum virgatum L., grown for biomass has been extensively researched where the annual precipitation >760 mm and the climate varies from humid to moist-subhumid. Research is needed for areas that receive <700 mm of precipitation, where the climate varies from dry-subhumid to semiarid. The objectives were to determine (1) the effect of nitrogen fertilization on biomass production, (2) the effect of residual nitrogen on biomass production, (3) the nitrogen yield from harvested biomass, and (4) the concentration of soil organic carbon (SOC) from switchgrass plots. Plots were fertilized annually with nitrogen at the rates of 0, 40, 80, and 120 kg ha^?1 from 2008 to 2011 and unfertilized from 2012 to 2015. The biomass yield varied with N rate × production year interactions (P < 0.05), and biomass yield as a function of N rate was either linear or curvilinear depending upon production year. When fertilized, the biomass yield averaged 4.4, 9.4, 11.6, and 13.2 ± 0.4 Mg ha^?1 for the 0, 40, 80, and 120 kg ha^?1 N rates, respectively. Residual nitrogen sustained high biomass yields for 1 year after fertilization ceased. The nitrogen harvested in biomass varied with N rate × production year interactions (P < 0.05), and the harvested nitrogen yield as a function of N rate was linear each year. Fertilization increased the concentration of SOC an average of 1.0 ± 0.2 mg g^?1 of soil. The data suggest that producers could occasionally skip a year of nitrogen fertilization without detrimentally impacting the production of switchgrass biomass.     

Nitrogen Fertilization Does Significantly Increase Yields of Stands of Miscanthus × giganteus and Panicum virgatum in Multiyear Trials in Illinois

The C4 perennial grasses Miscanthus × giganteus and Panicum virgatum (switchgrass) are emerging bioenergy crops. They are attractive because they are productive and recycle nutrients to the overwintering belowground rhizomes, before the dry shoots are harvested. They are therefore expected to require minimal fertilizer inputs, a desirable trait for any crop. Until now, Europe has had the only long-term trials of M. × giganteus, and these have either shown no or a small effect of nitrogen fertilization, while trials of P. virgatum in the USA have shown a clear positive effect of N fertilization. This study exploited the first long-term trials of M. × giganteus in the USA, and first side-by-side comparison with P. virgatum, to test the hypothesis that N fertilization would only improve yields of the latter. A split-plot N fertility treatment (0, 67, 134, and 202 kg(N)?ha^?1) was added to >5-year-old replicated stands of the two crops at seven locations on contrasting soils in the US Midwest. Averaged across all locations, M. × giganteus yields increased significantly from 23.4 Mg ha^?1 with no N fertilization to 28.9 Mg ha^?1 (+25 %) at a N application rate of 202 kg ha^?1. P. virgatum also showed significant yield increases from 10.33 Mg ha^?1 at 0 kg(N)?ha^?1 to 13.6 Mg ha^?1 (+32 %) at 202 kg(N)?ha^?1. Both species therefore responded to N fertilization and to a similar extent. The increase per unit of added N was small compared to crops such as Zea mays and unlikely to be economically worthwhile. Nitrogen fertilization arrested most of the long-term yield decline that would otherwise have occurred in P. virgatum, but eliminated only about 40 % of the decline observed in M. × giganteus, suggesting additional causal factors for long-term yield decline in this crop. While the crops responded to nitrogen addition at some locations, they did not at others. Therefore a one-case-fits-all optimum fertilization rate cannot be prescribed.     

Multilocation Corn Stover Harvest Effects on Crop Yields and Nutrient Removal

Corn (Zea mays L.) stover was identified as an important feedstock for cellulosic bioenergy production because of the extensive area upon which the crop is already grown. This report summarizes 239 site-years of field research examining effects of zero, moderate, and high stover removal rates at 36 sites in seven different states. Grain and stover yields from all sites as well as N, P, and K removal from 28 sites are summarized for nine longitude and six latitude bands, two tillage practices (conventional vs no tillage), two stover-harvest methods (machine vs calculated), and two crop rotations {continuous corn (maize) vs corn/soybean [Glycine max (L.) Merr.]}. Mean grain yields ranged from 5.0 to 12.0 Mg ha^?1 (80 to 192 bu ac^?1). Harvesting an average of 3.9 or 7.2 Mg ha^?1 (1.7 or 3.2 tons ac^?1) of the corn stover resulted in a slight increase in grain yield at 57 and 51 % of the sites, respectively. Average no-till grain yields were significantly lower than with conventional tillage when stover was not harvested, but not when it was collected. Plant samples collected between physiological maturity and combine harvest showed that compared to not harvesting stover, N, P, and K removal was increased by 24, 2.7, and 31 kg ha^?1, respectively, with moderate (3.9 Mg ha^?1) harvest and by 47, 5.5, and 62 kg ha^?1, respectively, with high (7.2 Mg ha^?1) removal. This data will be useful for verifying simulation models and available corn stover feedstock projections, but is too variable for planning site-specific stover harvest.     

Switchgrass for forage and bioenergy: harvest and nitrogen rate effects on biomass yields and nutrient composition

Switchgrass (Panicum virgatum L.) may have value as forage and a bioenergy feedstock. Our objective was to evaluate how harvest system and N fertilizer rates affected biomass yield and nutrient composition of young stands of switchgrass (cv. Alamo) in the southern Great Plains, USA. Nitrogen fertilization increased biomass yields from 10.4, 10.8, and 12.2 Mg ha^?1 at 0 kg N?ha^?1 to 13.7, 14.6, and 21.0 Mg ha^?1 at 225 kg N?ha^?1 when harvested after seed set (October), after frost (December), and twice per year after boot stage (July) and frost, respectively. Nutrient concentrations and removal were generally twice as great when biomass was harvested twice versus once per year. Precipitation strongly affected biomass yields across the two years of these experiments. When late-summer precipitation is available to support regrowth in this environment, harvesting switchgrass twice per year will result in greater biomass yields. Harvesting twice per year, however, will increase fertilization requirements and reduce feedstock biomass quality. Switchgrass harvested during mid-summer after boot stage was of poor forage quality. To have value as a dual-purpose forage and bioenergy feedstock, switchgrass would need to be utilized during spring to early summer while in a vegetative stage.     

Seasonal Changes in Shoot and Root Nitrogen Distribution in Switchgrass (Panicum virgatum)

Switchgrass is a promising bioenergy source that is perennial, productive, native to a broad geographic region, and can grow on marginal, nitrogen (N)-poor soils. Understanding N dynamics in switchgrass is critical to predicting productivity, conserving N, and optimizing the timing of harvest. We examined seasonal changes in N distribution in above- and belowground tissues in switchgrass to quantify N retranslocation rates. Above- and belowground biomass from three sites (two in PA and one in NE) were collected and analyzed for biomass growth and N concentrations at 30-day intervals from June through October. Total living plant mass ranged from 10.3?±?2.4 standard error (SE) to 14.9?±?2.5 SE Mg ha^?1. Belowground mass comprised 52–57 % of total mass. Blades had the highest N concentration during summer, ranging from 6 to 22 g kg^?1 N. Aboveground N concentrations decreased from September until autumn senescence, whereas belowground N concentration increased from August until senescence. Across the sites, total N retranslocated from aboveground to belowground components between September and October averaged 16.5?±?7.1 (SE)?kg ha^?1 N representing 26.7 % of the average maximum N content of aboveground biomass. Based on N fertilizer costs, delayed harvest would conserve some N and provide financial savings on fertilizer ($9 ha^?1) if harvest occurs after senescence but before overwinter biomass loss. However, biomass losses of even 10 % will negate potential economic savings accrued from N retention. To maximize environmental and economic savings from N retranslocation and to simultaneously minimize harvest losses, it would be optimal to harvest switchgrass as soon as possible after complete senescence.     

Growth Variation Among Hybrid Poplar Varieties in Michigan,USA and the Implications for Commercial Biomass Production.

Variability in biomass yield among 13 varieties of Populus hybrids was examined during a 7-year rotation in a network of 4 field trials in Michigan, USA. Seventh-year yield varied by site, averaging from 15.1 Mg ha^?1 in the north to 35.2 Mg ha^?1 in the south. Yield varied among varieties, ranging from 3.0 Mg ha^?1 for DN70 in the north to 52.9 Mg ha^?1 for NM2 in the south. Yield was most strongly correlated with growing season temperatures and rainfall but less with edaphic factors throughout the network. Twenty-eight percent of the total variation in individual tree weight was due to location effects and another 28% was due to genetic factors, including strong genotype by environment interactions. Even though each 64-tree plot comprised genetically identical clones, the remaining 44% of total observed variation among trees occurred within these plots. Five varieties that performed well throughout the network were identified as an elite cohort for general commercial use throughout the region. This cohort yielded as much as 50% more biomass than random selections. Certain varieties did well at one location while not at others because of strong genotype by environment interactions. Locally chosen elite cohorts produced as much as 5% more biomass than the regional elite cohort. Varietal ranking did change over time but it was possible to reliably identify the regional cohort after 3 years and local cohorts after 4 years. Local, long-term testing of Populus hybrids will be necessary to optimize commercial biomass yields and thereby maximize financial returns to growers.     

Do Yield and Quality of Big Bluestem and Switchgrass Feedstock Decline over Winter?

Switchgrass (Panicum virgatum L.) and big bluestem (Andropogon gerdardii Vitman) are potential perennial bioenergy feedstocks. Feedstock storage limitations, labor constraints for harvest, and environmental benefits provided by perennials are rationales for developing localized perennial feedstock as an alternative or in conjunction with annual feedstocks (i.e., crop residues). Little information is available on yield, mineral, and thermochemical properties of native species as related to harvest time. The study’s objectives were to compare the feedstock quantity and quality between grasses harvested in the fall or the following spring. It was hypothesized that biomass yield may decline, but translocation and/or leaching of minerals from the feedstock would improve feedstock quality. Feedstock yield did not differ by crop, harvest time, or their interactions. Both grasses averaged 6.0 Mg ha^?1 (fall) and 5.4 Mg ha^?1 (spring) with similar high heating value (17.7 MJ kg^?1). The K/(Ca?+?Mg) ratio, used as a quality indicator declined to below a 0.5 threshold, but energy yield (Megajoule per kilogram) decreased 13 % by delaying harvest until spring. Only once during the four study-years were conditions ideal for early spring harvest, in contrast during another spring, very muddy conditions resulted in excessive soil contamination. Early spring harvest may be hampered by late snow, lodging, and muddy conditions that may delay or prevent harvest, and result in soil contamination of the feedstock. However, reducing slagging/fouling potential and the mass of mineral nutrients removed from the field without a dramatic loss in biomass or caloric content are reasons to delay harvest until spring.     

Crop Residue Mass Needed to Maintain Soil Organic Carbon Levels: Can It Be Determined?

Corn’s (Zea mays L.) stover is a potential nonfood, herbaceous bioenergy feedstock. A vital aspect of utilizing stover for bioenergy production is to establish sustainable harvest criteria that avoid exacerbating soil erosion or degrading soil organic carbon (SOC) levels. Our goal is to empirically estimate the minimum residue return rate required to sustain SOC levels at numerous locations and to identify which macroscale factors affect empirical estimates. Minimum residue return rate is conceptually useful, but only if the study is of long enough duration and a relationship between the rate of residue returned and the change in SOC can be measured. About one third of the Corn Stover Regional Partnership team (Team) sites met these criteria with a minimum residue return rate of 3.9?±?2.18 Mg stover ha^?1 yr^?1, n?=?6. Based on the Team and published corn-based data (n?=?35), minimum residue return rate was 6.38?±?2.19 Mg stover ha^?1 yr^?1, while including data from other cropping systems (n?=?49), the rate averaged 5.74?±?2.36 Mg residue ha^?1 yr^?1. In broad general terms, keeping about 6 Mg residue ha^?1 yr^?1 maybe a useful generic rate as a point of discussion; however, these analyses refute that a generic rate represents a universal target on which to base harvest recommendations at a given site. Empirical data are needed to calibrate, validate, and refine process-based models so that valid sustainable harvest rate guidelines are provided to producers, industry, and action agencies.     

Impact of Nitrogen Fertilization to Short-Rotation Willow Coppice Plantations Grown in Sweden on Yield and Economy

A fertilization trial was carried out in established short-rotation willow coppice (SRWC) plantations of two bred varieties of willow (Salix spp.; "Tora" and "Jorr") at five sites in central Sweden between 2008 and 2010. Mineral nitrogen was applied at four different rates: No fertilization (Control), 160 kg nitrogen ha^?1 as a single dose after harvest (Economy), 60–100–60 kg nitrogen ha^?1 in year 1–2–3 (Normal), and 160 kg nitrogen ha^?1 year^?1 in years 1–3 (Intensive), using a randomized block design with four replicates. The yield response (biomass increase per kg fertilizer nitrogen) was 65, 67 and 46 kg kg^?1 in the Economy, Normal and Intensive treatments, respectively. The results from the fertilization trial were used for economic calculations of different fertilization strategies given varying costs for fertilization and marginal value of the increased yield (price received for wood chips minus the costs for harvest and transportation of wood chips to a district heating plant). Comparative calculations were made based on data from a previous fertilization trial during the first cutting cycle of old, non-bred varieties. The calculations showed positive net present values of fertilizing bred willow varieties given a realistic fertilization response and a price for wood chips close to the market price for forestry-based wood chips in Sweden.     

Litterfall production, decomposition and nutrient use efficiency varies with tropical forest types in Xishuangbanna, SW China: a 10-year study

Litterfall production, decomposition and nutrient use efficiency in three different tropical forest ecosystems in SW China were studied for 10 years. Annual mean litterfall production in tropical seasonal forest (TSF) (9.47?±?1.65 Mg ha^?1) was similar to that in man-made tropical forest (MTF) (9.23?±?1.29 Mg ha^?1) (P?>?0.05) but both were significantly lower than that in secondary tropical forest (STF) (12.96?±?1.71 Mg ha^?1) (P?<?0.05). The annual variation of litterfall was greater in TSF (17.4%, P?<?0.05) than in MTF (14.0%) or STF (13.2%). The annual mean decomposition rate of litterfall increased followed the order of MTF (2.72)?<?TSF (3.15)?<?STF (3.50) (P?<?0.05), which was not correlated with annual precipitation or annual mean temperature, but was rather related to litter quality. The nutrient use efficiency was found to be element-dependent and to vary significantly among the three forest types (P?<?0.05). These results indicate that litterfall production and decomposition rates in different tropical forest systems are related to plant species composition and are influenced strongly by coexisting species and their life stage (age) but less so by the species richness. Constructing multi-species and multistory man-made tropical forest is an effective way to enhance biological productivity and maintain soil nutrients on degraded tropical land.     

Maize Kernel Hardness,Endosperm Zein Profiles,and Ethanol Production

Maize (Zea mays L.) grain is an important feedstock for the ethanol-producing industry. However, little is known about the optimum grain quality for optimizing ethanol yielding efficiencies. We specifically investigated the response of ethanol yields (L Mg^?1) to kernel hardness, and its physiological determinant endosperm zein protein profiles, as affected by genotype selection, field nitrogen (N) fertilization, and crop growth environment. We measured ethanol yield and related this to different kernel hardness indicators, kernel composition, and zein profiles. We also described changes in field ethanol yield (L ha^?1), by taking into account the crop yield (Mg ha^?1). Hard endosperm genotypes always yielded less ethanol than softer endosperm ones per grain mass (L Mg^?1). Higher N fertilization rates increased kernel hardness and decreased ethanol yield (L Mg^?1) on soft endosperm dented genotypes but had no effect on hard endosperm ones. Ethanol yield was negatively correlated with kernel density, kernel protein concentration, and Z1 and Z2 zein fractions. Within Z2, 15 kDa β-zein explained the largest ethanol yield variation generated by genotypes, N fertilizations, and growth environments. However, and although these differences were as large as 10%, ethanol field yield (L ha^?1) was mainly driven by crop yields (r ² 0.98) due to the large crop yield (Mg ha^?1) differences observed across treatments. Together, our results helped describe the magnitude that changes in maize kernel hardness can have over ethanol yield, both through genotype selection or crop management. A particular Z2 zein protein rises as relevant for future genetic manipulations of maize ethanol yield determination.     

Biomass Production and Composition of Perennial Grasses Grown for Bioenergy in a Subtropical Climate Across Florida, USA

Carbohydrate and lignin composition of feedstock materials are major factors in determining their bioenergy potential. This study was conducted to quantify dry biomass yield and the carbohydrate and lignin composition of six potential biofuel grasses (elephantgrass, energycane, sweetcane, giant reed, giant miscanthus, and sugarcane) across three sites in Florida for plant (2009) and first ratoon (2010) crops. Dry biomass yields ranged from about 30 to 50 Mg ha^?1 and were generally greatest for elephantgrass, energycane, sweetcane, and sugarcane. Accordingly, total plant carbohydrate yields (20 to 25 Mg ha^?1) were comparable among sugarcane, energycane, sweetcane, and elephantgrass, but were generally less for giant reed and even less for giant miscanthus. However, the contribution of total extractable carbohydrates and total fiber carbohydrates to total plant carbohydrate yields differed among species. Sugarcane had the highest concentrations of extractable carbohydrates (219 to 356 mg g^?1), followed by energycane, then sweetcane, elephantgrass, and giant reed, with giant miscanthus having the lowest. Energycane and elephantgrass tended to have significantly more fiber glucose, and elephantgrass less xylose, than other species. Variability in total lignin concentrations on a fiber basis was relatively modest (250 to 285 mg g^?1) across species, but was generally highest in sweetcane and giant reed. Overall, elephantgrass and energycane were prime regional candidates for cellulosic conversion using fermentation processes due to high yields and favorable fiber characteristics, although energycane tended to have higher extractable carbohydrates.     

Switchgrass and Giant Miscanthus Biomass and Theoretical Ethanol Production from Reclaimed Mine Lands

Switchgrass (Panicum virgatum L.) and giant miscanthus (Miscanthus x giganteus Greef & Deuter ex Hodkinson & Renvoize) are productive on marginal lands in the eastern USA, but their productivity and composition have not been compared on mine lands. Our objectives were to compare biomass production, composition, and theoretical ethanol yield (TEY) and production (TEP) of these grasses on a reclaimed mined site. Following 25 years of herbaceous cover, vegetation was killed and plots of switchgrass cultivars Kanlow and BoMaster and miscanthus lines Illinois and MBX-002 were planted in five replications. Annual switchgrass and miscanthus yields averaged 5.8 and 8.9 Mg dry matter ha^?1, respectively, during 2011 to 2015. Cell wall carbohydrate composition was analyzed via near-infrared reflectance spectroscopy with models based on switchgrass or mixed herbaceous samples including switchgrass and miscanthus. Concentrations were higher for glucan and lower for xylan in miscanthus than in switchgrass but TEY did not differ (453 and 450 L Mg^?1, respectively). In response to biomass production, total ethanol production was greater for miscanthus than for switchgrass (5594 vs 3699 L ha^?1), did not differ between Kanlow and BoMaster switchgrass (3880 and 3517 L ha^?1, respectively), and was higher for MBX-002 than for Illinois miscanthus (6496 vs 4692 L ha^?1). Relative to the mixed feedstocks model, the switchgrass model slightly underpredicted glucan and slightly overpredicted xylan concentrations. Estimated TEY was slightly lower from the switchgrass model but both models distinguished genotype, year, and interaction effects similarly. Biomass productivity and TEP were similar to those from agricultural sites with marginal soils.     

Influence of soil texture and crop management on the productivity of miscanthus (Miscanthus × giganteus Greef et Deu.) in the Mediterranean

Biomass productivity is the main favorable trait of candidate bioenergy crops. Miscanthus × giganteus is a promising species, due to its high‐yield potential and positive traits including low nutrient requirements and potential for C sequestration in soils. However, miscanthus productivity appears to be mostly related to water availability in the soil. This is important, particularly in Mediterranean regions where the risk of summer droughts is high. To date, there have been no studies on miscanthus responses under different soil conditions, while only a few have investigated the role of different crop managements, such as irrigation and nitrogen fertilization, in the Mediterranean. Therefore, the effects of contrasting soil textures (i.e. silty‐clay‐loam vs. sandy‐loam) and alternative agricultural intensification regimes (i.e. rainfed vs. irrigated and 0, 50, 100 kg ha^?1 nitrogen fertilization), on miscanthus productivity were evaluated at three different harvest times for two consecutive years. Our results confirmed the importance of water availability in determining satisfactory yields in Mediterranean environments, and how soil and site characteristics strongly affect biomass production. We found that the aboveground dry yields varied between 5 Mg ha^?1 up to 29 Mg ha^?1. Conversely, nitrogen fertilization played only a minor role on crop productivity, and high fertilization levels were relatively inefficient. Finally, a marked decrease, of up to ?40%, in the aboveground yield occurred when the harvest time was delayed from autumn to winter. Overall, our results highlighted the importance of determining crop responses on a site‐by‐site basis, and that decisions on the optimal harvest time should be driven by the biomass end use and other long‐term considerations, such as yield stability and the maintenance of soil fertility.     

Agricultural Management of Switchgrass for Fuel Quality and Thermal Energy Yield on Highly Erodible Land in the Driftless Area of Southwest Wisconsin

Converting row crop production to a perennial grass crop on highly erodible land has numerous benefits. Switchgrass, grown as a biofuel crop, can provide soil conservation benefits as a perennial crop and also provide economic value to the grower. However, little information exists regarding switchgrass management and production on these lands. The objectives of this study were to determine the effect of two management practices, nitrogen (N) fertilizer rate (0, 56, 112, 168, and 224 kg ha^?1) and harvest timing (mid-fall, late-fall, and spring), on: (1) dry matter (DM) yield, (2) switchgrass quality components (moisture, ash, and chloride (Cl^?) concentrations), and (3) combustion energy content and yield. The study was conducted in 2009 and 2010 on highly erodible lands in the Driftless Area of southwest Wisconsin. Results showed a positive response of switchgrass DM to N fertilizer, with no yield gain above 112 kg ha^?1 of N, although application of N increased Cl^? concentrations. Harvest timing also affected switchgrass yield, with decreases in yield observed with progressively later harvest timings; this yield decrease was slightly greater compared with previous studies. Progressively later harvest timings led to a decrease in moisture, ash concentration, and Cl^? concentration in both years. Energy content of switchgrass was not significantly affected by management. Energy yields, similar to DM yields, were maximized with 112 kg ha^?1 of N with a mid-fall harvest. The similarities between this study and other research indicate there is a universal response of switchgrass to N in the northern USA and yields determined in this study indicate that highly erodible lands in the Driftless Area can be used to produce switchgrass at regionally expected yields.     

Management of Warm- and Cool-Season Grasses for Biomass on Marginal Lands: I. Yield and Soil Fertility Status

Switchgrass (Panicum virgatum L.), tall fescue [Lolium arundinaceum (Schreb.)], and reed canarygrass (Phalaris arundinacea L.) are known for high biomass productivity and for various traits that make these species more suitable for marginal environmental growing conditions. The goal of this study was to evaluate the impact of organic vs. inorganic fertilizer application on grass biomass production and soil nutrient status. Switchgrass, tall fescue, and reed canarygrass were established on a sandy soil and a clay soil at the Cornell University Willsboro Research Farm in Willsboro, NY. The experiment was a split-split plot randomized block design with six replicates. Sites were whole plots, grass species were subplots, and fertility treatments were sub-subplots. The six treatments were (1) 168 kg ha^?1 of N fertilizer for cool-season grasses, 84 kg ha^?1 for switchgrass; (2) 56 kg ha^?1 of 0-46-0 P fertilizer plus N (#1); (3) 112 kg ha^?1 of 0-0-60 K fertilizer plus N (#1); (4) 89.6 Mg dairy manure ha^?1; (5) 44.8 Mg dairy manure compost ha^?1; and (6) no fertilizer applied (control plots). Switchgrass with a single harvest per season yielded on average 13.0 Mg ha^?1, while tall fescue and reed canarygrass averaged 8.4 and 7.7 Mg ha^?1, respectively, under two-cut systems. Switchgrass with no fertilization produced 84% of maximum yield of fertilized treatments. Application of a similar amount of organic N with fresh and composted dairy manure resulted in greater yields for fresh dairy manure. Organic fertilizers strongly impacted the P and K status of soils. Switchgrass is capable of high yields in marginal environments and can provide a land base for environmentally acceptable application of animal manure, although from a yield standpoint it is not very responsive to fertilizer applications.     

Litter dynamics and fine root production in Schizolobium parahyba var. amazonicum plantations and regrowth forest in Eastern Amazon

Forest plantations and agroforestry systems with Schizolobium parahyba var. amazonicum have greatly expanded in the Brazilian Amazon, generally as an alternative for reforesting degraded areas. To our knowledge there are no reports of above- and below-ground production in these forest systems. We quantified litter and fine root production in 6-yr old Schizolobium-based plantation forests (monospecific: MON, mixture: MIX, and agroforestry system: AFS) and in ~25-yr old regrowth forest (REG) over 8–12 months. We used litter traps and ingrowth cores to quantify litter and fine root production, respectively. Annual litter production was significantly lower in Schizolobium-based plantations (mean ± standard error, MON?=?5.92?±?0.15, MIX?=?6.08?±?0.13, AFS?=?6.63?±?0.13 Mg ha^?1 year^?1) than in regrowth forest (8.64?±?0.08 Mg ha^?1 year^?1). Schizolobium-based plantations showed significantly higher litter stock (MON?=?7.7?±?1.0, MIX?=?7.4?±?0.1 Mg ha^?1) than REG (5.9?±?1.3 Mg ha^?1). Total fine root production over an 8-month period was significantly higher in Schizolobium-based plantations (MON?=?3.8?±?0.2, MIX?=?3.4?±?0.2, AFS?=?2.7?±?0.1 Mg ha^?1) than in REG (1.1?±?0.03 Mg ha^?1). Six-yr old Schizolobium-based plantations and ~25-yr old regrowth forests showed comparable rates of litter + fine root production, suggesting that young forest plantations may be an interesting alternative to restore degraded areas due to early reestablishment of organic matter cycling under the studied conditions.