• Authors:
    • Boe, A.
    • Wimberly, M. C.
    • Tulbure, M. G.
    • Owens, V. N.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 146
  • Issue: 1
  • Year: 2012
  • Summary: The U.S. Renewable Fuel Standard calls for 136 billion liters of renewable fuels production by 2022. Switchgrass (Panicum virgatum L.) has emerged as a leading candidate to be developed as a bioenergy feedstock. To reach biofuel production goals in a sustainable manner, more information is needed to characterize potential production rates of switchgrass. We used switchgrass yield data and general additive models (GAMs) to model lowland and upland switchgrass yield as nonlinear functions of climate and environmental variables. We used the GAMs and a 39-year climate dataset to assess the spatio-temporal variability in switchgrass yield due to climate variables alone. Variables associated with fertilizer application, genetics, precipitation, and management practices were the most important for explaining variability in switchgrass yield. The relationship of switchgrass yield with climate variables was different for upland than lowland cultivars. The spatio-temporal analysis showed that considerable variability in switchgrass yields can occur due to climate variables alone. The highest switchgrass yields with the lowest variability occurred primarily in the Corn Belt region, suggesting that prime cropland regions are the best suited for a constant and high switchgrass biomass yield. Given that much lignocellulosic feedstock production will likely occur in regions with less suitable climates for agriculture, interannual variability in yields should be expected and incorporated into operational planning.
  • Authors:
    • Lindquist, J. L.
    • Drijber, R. A.
    • Bernards, M. L.
    • Francis, C. A.
    • Wortman, S. E.
  • Source: AGRONOMY JOURNAL
  • Volume: 104
  • Issue: 5
  • Year: 2012
  • Summary: Previous studies have demonstrated benefits of individual cover crop species, but the value of diverse cover crop mixtures has received less attention. The objectives of this research were to determine the effects of spring-sown cover crop mixture diversity and mechanical cover crop termination method on cover crop and/or cash crop productivity, soil moisture and N, and profitability in an organic cropping system. An experiment was conducted between 2009 and 2011 near Mead, NE, where mixtures of two (2CC), four (4CC), six (6CC), and eight (8CC) cover crop species, or a summer annual weed mixture were included in a sunflower-soybean-corn rotation. Cover crops were terminated in late May using a field disk or sweep plow undercutter. Undercutting cover crops increased soil NO 3-N (0-20 cm) by 1.0 and 1.8 mg NO 3-N kg -1 relative to disk incorporation in 2010 and 2011, respectively. Cover crop mixtures often reduced soil moisture (0-8 cm) before main crop planting, though cover crop termination with the undercutter increased soil moisture content by as much as 0.024 cm 3 cm -3 compared to termination with the disk during early main crop growth. Crop yields were not influenced by cover crop mixture, but termination with the undercutter increased corn and soybean yield by as much as 1.40 and 0.88 Mg ha -1, respectively. Despite differences in productivity between spring cover crop mixtures and weed communities, crop yield was not different among these treatments; thus, profitability of the weed mixture-undercutter treatment combination was greatest due to reduced input costs.
  • Authors:
    • Lindquist, J. L.
    • Francis, C. A.
    • Wortman, S. E.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 3
  • Year: 2012
  • Summary: Achieving agronomic and environmental benefits associated with cover crops often depends on reliable establishment of a highly productive cover crop community. The objective of this study was to determine if cover crop mixtures can increase productivity and stability compared to single species cover crops, and to identify those components most active in contributing to or detracting from mixture productivity. A rainfed field experiment was conducted near Mead, NE, in 2010 and 2011. Eight individual cover crop species (in either the Brassicaceae [mustard] or Fabaceae [legume] family) and four mixtures of these species (two, four, six, and eight species combinations) were broadcast planted and incorporated in late March and sampled in late May. Shoot dry weights were recorded for sole crops and individual species within all mixtures. Sole crops in the mustard family were twice as productive (2428 kg ha -1) as sole crops in the legume family (1216 kg ha -1), averaged across 2 yr. The land equivalent ratios (LERs) for all mixtures in 2011 were >1.0, indicating mixtures were more productive than the individual components grown as sole crops. Improved performance in mixture may be related to the ecological resilience of mixed species communities in response to extreme weather events, such as hail. Partial LERs of species in the mustard family were consistently greater than those in the legume family, indicating that mustards dominated the mixtures. Results provide the basis for yield-stability rankings of spring-sown cover crop species and mixtures for the western Corn Belt.
  • Authors:
    • Khizar, A.
    • Abbasi, M. K.
  • Source: Ecological Engineering
  • Volume: 39
  • Issue: February
  • Year: 2012
  • Summary: Application of organic amendments to soil is an important management strategy for enhancing the restoration of degraded soils and providing better soil conditions to below-ground soil microbial composition and above-ground plant community development. This study was conducted to investigate the effect of organic amendments (poultry manure - PM; white clover residues - WCR), a mineral N fertilizer (urea N - UN), or mixtures of these fertilizers on microbial activity and nitrogen (N) mineralization through both soil analysis (laboratory incubation) and aboveground maize (Zea mays L) growth (pot experiment). In the incubation experiment, soil was amended with PM, WCR, PM + WCR, UN, UN + PM, UN + WCR, and UN + PM + WCR at the rate equivalent to 200 mg N kg(-1) soil. Pot experiment was conducted in a glasshouse using same amendments to examine the response of maize seedlings to these treatments. Organic amendments and UN applied alone or in mixtures increased soil microbial biomass compared to the control. Among N amendments, the highest evaluation of CO2-C (47.7 mg kg(-1) day(-1)), microbial biomass C (434 mg kg) and microbial biomass N (86 mg kg(-1)) were recorded in the UN + PM + WCR while the lowest values were recorded in UN. It is estimated that 9-18% of the applied N had been assimilated into microbial N pool after 105 days. Mineralization of N was higher in the fertilized soil and ranged between 85 and 192 mg N kg(-1) compared with 46 mg N kg(-1) in the control. The net cumulative N mineralized (NCNM) ranged between 43 and 169 mg kg(-1) while the net cumulative N nitrified (NCNN) ranged between 16 and 69%. Combined application of UN + PM + WCR exhibited the highest NCNM and NCNN. On average, percentage conversion of added N into NO3--N was: 21% from organic sources, 40% from UN and 52% from UN + organic sources. The apparent recovery of added N (ANR) from PM, WCR and PM + WCR was 20, 24 and 45%, respectively, while UN, UN + PM, UN + WCR and UN + PM + WCR exhibited 50, 57, 64, and 73% ANR, respectively. Results obtained from the pot experiment (on maize) were consistent with the total mineral N (TMN) released from different amendments and highly significant correlations existed between TMN and plant dry matter yield (r(2) = 0.92) and TMN and N uptake of plants (r(2) = 0.89). The present study demonstrates the existence of substantial amount of N reserve present in organic substrates, which can be transformed into inorganic N pool and can be taken into account as potential sources in the management of the nutrient poor soils and crop growth. (C) 2011 Published by Elsevier B.V.
  • Authors:
    • Voigt, T. B.
    • David, M. B.
    • Behnke, G. D.
  • Source: BioEnergy Research
  • Volume: 5
  • Issue: 4
  • Year: 2012
  • Summary: Understanding the effects of nitrogen (N) fertilization on Miscanthus x giganteus greenhouse gas emissions, nitrate leaching, and biomass production is an important consideration when using this grass as a biomass feedstock. The objective of this study was to determine the effect of three N fertilization rates (0, 60, and 120 kg N ha(-1) using urea as the N source) on nitrous oxide (N2O) and carbon dioxide (CO2) emissions, nitrogen leaching, and the biomass yields and N content of M. x giganteus planted in July 2008, and evaluated from 2009 through early 2011 in Urbana, Illinois, USA. While there was no biomass yield response to N fertilization rates in 2009 and 2010, the amount of N in the harvested biomass in 2010 was significantly greater at the 60 and 120 kg N ha(-1) N rates. There was no significant CO2 emission response to N rates in 2009 or 2010. Similarly, N fertilization did not increase cumulative N2O emissions in 2009, but cumulative N2O emissions did increase in 2010 with N fertilization. During 2009, nitrate (NO (3) (-) ) leaching at the 50-cm soil depth was not related to fertilization rate, but there was a significant increase in NO (3) (-) leaching between the 0 and 120 kg N ha(-1) treatments in 2010 (8.9 and 28.9 kg NO3-N ha(-1) year(-1), respectively). Overall, N fertilization of M. x giganteus led to N2O releases, increased fluxes of inorganic N (primarily NO (3) (-) ) through the soil profile; and increased harvested N without a significant increase in biomass production.
  • Authors:
    • Klakegg, O.
    • Janzen, H. H.
    • Skjelvag, A. O.
    • Bonesmo, H.
    • Tveito, O. E.
  • Source: Agricultural Systems
  • Volume: 110
  • Issue: July
  • Year: 2012
  • Summary: To increase food production while mitigating climate change, cropping systems in the future will need to reduce greenhouse gas emission per unit of production. We conducted an analysis of 95 arable farms in Norway to calculate farm scale emissions of greenhouse gases, expressed both as CO2 eq per unit area, and CO2 eq per kg DM produced and to describe relationships between the farms' GHG intensities and heir economic efficiencies (gross margin). The study included: (1) design of a farm scale model for net GHG emission from crop production systems; (2) establishing a consistent farm scale data set for the farms with required soil, weather, and farm operation data; (3) a stochastic simulation of the variation in the sources of GHG emission intensities, and sensitivity analysis of selected parameters and equations on GHG emission intensities; and (4) describing relationships between GHG emission intensities and gross margins on farms. Among small seed and grain crops the variation in GHG emissions per kg DM was highest in oilseed (emission intensity at the 75th percentile level was 1.9 times higher than at the 25th percentile). For barley, oats, spring wheat, and winter wheat, emissions per kg DM at the 75th percentile levels were between 1.4 and 1.6 times higher than those at the 25th percentiles. Similar trends were observed for emissions per unit land area. Invariably soil N2O emission was the largest source of GHG emissions, accounting for almost half of the emissions. The second largest source was the off farm manufacturing of inputs (similar to 25%). Except for the oilseed crop, in which soil carbon (C) change contributed least, the on farm emissions due to fuel use contributed least to the total GHG intensities (similar to 10%). The soil C change contributed most to the variability in GHG emission intensities among farms in all crops, and among the sensitivity elasticities the highest one was related to environmental impacts on soil C change. The high variation in GHG intensities evident in our study implies the potential for significant mitigation of GHG emissions. The GHG emissions per kg DM (intensity) decreased with increasing gross margin in grain and oilseed crops, suggesting that crop producers have economic incentives to reduce GHG emissions. (c) 2012 Elsevier Ltd. All rights reserved,
  • Authors:
    • Pudelko, R.
    • Syp, A.
    • Faber, A.
    • Borzecka-Walker, M.
    • Mizak, K.
  • Source: Journal of Food, Agriculture & Environment
  • Volume: 10
  • Issue: 2
  • Year: 2012
  • Summary: In this article, we applied the Denitrification-Decomposition (DNDC) model to field trials using miscanthus plants grown on heavy and medium heavy soils in Poland. The DNDC model was calibrated and then validated against experimental data. Similar results were found between the simulated and measured values of yield. The difference between the simulated and measured values of yield was from 1.20 to 3.09 t ha(-1) yr(-1) and the RMSE was very low (1.67). Furthermore, the RRMSE was equal to 10.30%, which confirms the high accuracy of the predicted results. The calibrated model was used to simulate yield, as well as simulating the greenhouse gas (GHG) emissions (CO2, CH4, N2O) for miscanthus cultivation in Poland.
  • Authors:
    • Leytem, A. B.
    • Venterea, R. T.
    • Fixen, P. E.
    • Snyder, C. S.
    • Liebig, M. A.
    • Del Grosso, S. J.
    • Cavigelli, M. A.
    • McLain, J. E.
    • Watts, D. B.
  • Source: Frontiers in Ecology and the Environment
  • Volume: 10
  • Issue: 10
  • Year: 2012
  • Summary: The use of commercial nitrogen (N) fertilizers has led to enormous increases in US agricultural productivity. However, N losses from agricultural systems have resulted in numerous deleterious environmental impacts, including a continuing increase in atmospheric nitrous oxide (N2O), a greenhouse gas (GHG) and an important catalyst of stratospheric ozone depletion. Although associated with about 7% of total US GHG emissions, agricultural systems account for 75% of total US N2O emissions. Increased productivity in the crop and livestock sectors during the past 30 to 70 years has resulted in decreased N2O emissions per unit of production, but N2O emissions from US agriculture continue to increase at a rate of approximately 0.46 teragrams of carbon dioxide equivalents per year (2002-2009). This rate is lower than that during the late 20th century. Improvements in agricultural productivity alone may be insufficient to lead to reduced emissions; implementing strategies specifically targeted at reducing N2O emissions may therefore be necessary. Front Ecol Environ 2012; 10(10): 537-546, doi:10.1890/120054
  • Authors:
    • Lorenz, N.
    • Saxena, J.
    • Chaudhary, D. R.
    • Dick, R. P.
  • Source: Plant, Soil and Environment
  • Volume: 58
  • Issue: 6
  • Year: 2012
  • Summary: The use of switchgrass (Panicum virgatum L.) as an energy crop has gained great importance in past two decades due to its high biomass yields on marginal lands with low agricultural inputs and low maintenance requirements. Information on the allocation of photosynthetically fixed C in the switchgrass-soil system is important to understand the C flow and to quantify the sequestration of C in soils. The allocation of C-13 labeled photosynthates in shoot, root, soil, and in microbial biomass carbon (MBC) of rhizosphere and bulk soil of 45 days old, greenhouse grown-switchgrass was examined during 20 days C-13-CO2 pulse labeling period. The total C-13 recovered in the plant-soil system varied from 79% after 1 day to 42% after 20 days of labeling. After labeling, 54%, 40%, and 6% excess C-13 resided in shoot, root and soil, respectively on day 1; 27%, 61% and 11%, respectively on day 5 and 20%, 63% and 17%, respectively day 20 after labeling. The maximum incorporation of C-13 from roots into the MB of rhizosphere soil occurred within the first 24 h of labeling. The excess C-13 values of rhizosphere soil and rhizosphere MBC were significantly higher than excess C-13 values of bulk soil and the bulk soil MBC, respectively. The proportion of excess C-13 in soil as MBC declined from 92 to 15% in rhizosphere soil and from 79 to 18% in bulk soil, for 1 day and 20 days after labeling, respectively. The present study showed the effectiveness of C-13 labeling to examine the fate of recently photosynthesized C in soil-plant (switchgrass) system and dynamics of MBC.
  • Authors:
    • Decock, C.
    • Leakey, A. D. B.
    • Gray, S. B.
    • Venterea, R.
    • Chung, H.
    • Six, J.
  • Source: Soil Biology and Biochemistry
  • Volume: 51
  • Issue: August
  • Year: 2012
  • Summary: In order to predict and mitigate future climate change, it is essential to understand plant-mediated effects of elevated CO2 (eCO(2)) and O-3 (eO(3)) on N-cycling, including N2O emissions. This is of particular interest for agroecosystems. since N-cycling and N2O emissions are responsive to adaptive management. We investigated the interaction of soil moisture content with eCO(2) and eO(3) on potential N2O emissions from SoyFACE during a 28-day laboratory incubation experiment. We also assessed field N2O fluxes during 2 soybean-growing seasons. In addition, we sought to link previously observed changes in soybean growth and production to belowground processes over a longer time scale by analyzing changes in natural abundance stable isotope ratios of soil N (delta N-15). This method relies on the concept that soil delta N-15 can only change when inputs or outputs with an isotope signature different from that of soil N are altered. We found no major effects of eCO(2) and eO(3) on laboratory and field measured N2O emissions. Natural abundance isotope analyses suggested, however, a decrease in belowground allocation of biologically fixed N in combination with decreased total gaseous N loss by eCO(2), resulting in a tighter N cycle in the longer-term. In contrast, the isotope data suggested an increase in belowground allocation of biologically fixed N under eO(3), leading to increased gaseous N loss, most likely in the form of N-2. Given that effects of eCO(2) and eO(3) on N pools and instantaneous transformation rates in surface soil layers of this agroecosystem have been minimal, our results illustrate the importance of evaluating longer-term changes in N turnover rates. We conclude that eCO(2) decelerates whereas eO(3) accelerates N-cycling in the longer-term, but feedback through changed N2O emissions is not occurring in this soybean system. (C) 2012 Elsevier Ltd. All rights reserved.