• Authors:
    • Gerik, T. J.
    • Williams, J. R.
    • Blumenthal, J. M.
    • Potter, S. R.
    • Kemanian, A. R.
    • Meki, M. N.
  • Source: Agricultural Systems
  • Volume: 117
  • Year: 2013
  • Summary: There is an increased demand on agricultural systems in the United States and the world to provide food, fiber, and feedstock for the emerging bioenergy industry. The agricultural intensification that this requires could have positive and negative feedbacks in productivity and the environment. In this paper we used the simulation model EPIC to evaluate the impact of alternative tillage and management systems on grain sorghum (Sorghum bicolor L. Moench) production in central and south Texas and to provide long-term insights into the sustainability of the proposed systems as avenues to increase agricultural output. Three tillage systems were tested: conventional (CT), reduced (RT), and no-tillage (NT). These tillage systems were tested on irrigated and rainfed conditions, and in soils with varying levels of structural erosion control practices (no practice, contour tillage, and contours + terraces). Grain yield differed only slightly across the three tillage systems with an average grain yield of 5.7 Mg ha(-1). Over the course of 100-year simulations, NT and RT systems had higher soil organic carbon (SOC) storage (100 and 91 Mg ha(-1), respectively) than CT (85 Mg ha(-1)), with most of the difference originating in the first 25 years of the simulations. As a result, NT and RT systems showed lower net global warming potentials (GWPs) (0.20 and 0.50 Mg C ha(-1) year(-1)) than CT (0.60 Mg C ha(-1) year(-1)). Irrigated systems had 26% higher grain yields than rainfed systems; yet the high energy needed to pump irrigation water (0.10 Mg C ha(-1) year(-1)) resulted in a higher net GWP for irrigated systems (0.50 vs. 0.40 Mg C ha(-1) year(-1)). Contours and contours + terraces had minimal impact on grain yields, SOC storage and GWP. No-till was the single technology with the largest positive impact on GWP and preservation or enhancement of SOC. Overall, the impact of individual tillage cropping systems on GWP seems to be decoupled from the productivity of a given location as determined by weather or soil type. When expressed per unit of output, high yield locations have a much lower GWP than low yield locations and would be therefore prime targets for production intensification. Published by Elsevier Ltd.
  • Authors:
    • Keeton, W. S.
    • Mika, A. M.
  • Source: GCB Bioenergy
  • Volume: 5
  • Issue: 3
  • Year: 2013
  • Summary: With growing interest in wood bioenergy there is uncertainty over greenhouse gas emissions associated with offsetting fossil fuels. Although quantifying postharvest carbon (C) fluxes will require accurate data, relatively few studies have evaluated these using field data from actual bioenergy harvests. We assessed C reductions and net fluxes immediately postharvest from whole-tree harvests (WTH), bioenergy harvests without WTH, and nonbioenergy harvests at 35 sites across the northeastern United States. We compared the aboveground forest C in harvested with paired unharvested sites, and analyzed the C transferred to wood products and C emissions from energy generation from harvested sites, including indirect emissions from harvesting, transporting, and processing. All harvests reduced live tree C; however, only bioenergy harvests using WTH significantly reduced C stored in snags (P<0.01). On average, WTH sites also decreased downed coarse woody debris C while the other harvest types showed increases, although these results were not statistically significant. Bioenergy harvests using WTH generated fewer wood products and resulted in more emissions released from bioenergy than the other two types of harvests, which resulted in a greater net flux of C (P<0.01). A Classification and Regression Tree analysis determined that it was not the type of harvest or amount of bioenergy generated, but rather the type of skidding machinery and specifics of silvicultural treatment that had the largest impact on net C flux. Although additional research is needed to determine the impact of bioenergy harvesting over multiple rotations and at landscape scales, we conclude that operational factors often associated with WTH may result in an overall intensification of C fluxes. The intensification of bioenergy harvests, and subsequent C emissions, that result from these operational factors could be reduced if operators select smaller equipment and leave a portion of tree tops on site.
  • Authors:
    • Fingerman, K.
    • Torn, M. S.
    • Mishra, U.
  • Source: GCB Bioenergy
  • Volume: 5
  • Issue: 4
  • Year: 2013
  • Summary: Interest in bioenergy crops is increasing due to their potential to reduce greenhouse gas emissions and dependence on fossil fuels. We combined process-based and geospatial models to estimate the potential biomass productivity of miscanthus and its potential impact on soil carbon stocks in the croplands of the continental United States. The optimum (climatic potential) rainfed productivity for field-dried miscanthus biomass ranged from 1 to 23Mgbiomassha-1yr-1, with a spatial average of 13Mgha-1yr-1 and a coefficient of variation of 30%. This variation resulted primarily from the spatial heterogeneity of effective rainfall, growing degree days, temperature, and solar radiation interception. Cultivating miscanthus would result in a soil organic carbon (SOC) sequestration at the rate of 0.16-0.82MgCha-1yr-1 across the croplands due to cessation of tillage and increased biomass carbon input into the soil system. We identified about 81millionha of cropland, primarily in the eastern United States, that could sustain economically viable (>10Mgha-1yr-1) production without supplemental irrigation, of which about 14millionha would reach optimal miscanthus growth. To meet targets of the US Energy Independence and Security Act of 2007 using miscanthus as feedstock, 19millionha of cropland would be needed (spatial average 13Mgha-1yr-1) or about 16% less than is currently dedicated to US corn-based ethanol production.
  • Authors:
    • Sawyer, J. E.
    • Castellano, M. J.
    • Mitchell, D. C.
    • Pantoja, J.
  • Source: Soil Science Society of America Journal
  • Volume: 77
  • Issue: 5
  • Year: 2013
  • Summary: Nitrous oxide (N2O) emission from denitrification in agricultural soils often increases with N fertilizer and soil nitrate (NO3) concentrations. Overwintering cover crops in cereal rotations can decrease soil NO3 concentrations and may decrease N2O emissions. However, mineralizable C availability can be a more important control on N2O emission than NO3 concentration in fertilized soils, and cover crop residue provides mineralizable C input. We measured the effect of a winter rye (Secale cereale L.) cover crop on soil N2O emissions from a maize (Zea mays L.) cropping system treated with banded N fertilizer at three rates (0, 135, and 225 kg N ha(-1)) in Iowa. In addition, we conducted laboratory incubations to determine if potential N2O emissions were limited by mineralizable C or NO3 at these N rates. The rye cover crop decreased soil NO3 concentrations at all N rates. Although the cover crop decreased N2O emissions when no N fertilizer was applied, it increased N2O emissions at an N rate near the economic optimum. In laboratory incubations, N2O emissions from soils from fertilizer bands did not increase with added NO3, but did increase with added glucose. These results show that mineralizable C availability can control N2O emissions, indicating that C from cover crop residue increased N2O emissions from fertilizer band soils in the field. Mineralizable C availability should be considered in future evaluations of cover crop effects on N2O emissions, especially as cover crops are evaluated as a strategy to mitigate agricultural greenhouse gas emissions.
  • Authors:
    • Teague, T. G.
    • Niederman, Z.
    • Danforth, D. M.
    • Nalley, L. L.
  • Source: Journal of Cotton Science
  • Volume: 17
  • Issue: 2
  • Year: 2013
  • Summary: Greenhouse gas (GHG) emissions are a growing concern for agricultural producers given increased pressure from government, consumers and retail purchasers. This study addresses the changes in greenhouse gas emissions in cotton over time (using years 1997, 2005 and 2008) due to changing production methods including tillage and seed technology. Time series data in this study comes from a single farm in Arkansas with detailed records of seed used, all inputs used (e.g. fertilizers, agrochemicals, irrigation), as well as machinery and tillage type for each of over 121 fields over 11 growing seasons. Results indicate yields increased dramatically (68%) over that time, due primarily to seed technology. At the same time, agrochemical use and fuel use decreased in 2008, primarily due to Bollgard II Roundup Ready Flex seed technology and the resulting reduced tillage. Reduced inputs can result in lower costs for producers, as well as reduced greenhouse gas emissions. Increasing yields with reduction in input use reduces the overall greenhouse gas emissions per pound of cotton produced, resulting in benefits to producers, consumers who demand such traits, and the environment. However, due to the proliferation of glyphosate-resistant pigweed ( Amaranthus palmeri), the decreases in greenhouse gas emissions per pound of cotton that were observed over the past decade may be reversed.
  • Authors:
    • Omonode, R.
    • Vyn, T.
  • Source: Agronomy Journal
  • Volume: 105
  • Issue: 6
  • Year: 2013
  • Summary: Simultaneous application of nitrification inhibitors and fertilizer N has the potential to delay nitrification processes and reduce atmospheric N loss through N2O emissions. A 2-yr study was conducted to assess the effects of newly available water-soluble nitrapyrin (Instinct) [2-chloro-6-(trichloromethyl) pyridine] on the nitrification kinetics and N2O emissions from urea-NH4NO3 (UAN) band applied to somewhat poorly drained and moderately well-drained silt loam soils in Indiana. The UAN fertilizer, with or without nitrapyrin, was injected post-emergence between corn (Zea mays L.) rows that were 76 cm apart. Soil samples were taken at various increments from the band centers at 1- to 2-wk intervals for up to 14 wk and analyzed for NH4- and NO3-N concentrations. Nitrification rates were determined using appropriate kinetic models. Greenhouse gas samples were collected weekly for 7 to 10 wk and biweekly thereafter for an additional 2 to 4 wk. Our results showed that UAN nitrification followed first-order kinetics, with significantly greater nitrification rate constants without nitrapyrin. On average, UAN half-life was about 15 d without nitrapyrin and 25 d when coapplied with nitrapyrin. Nitrapyrin reduced N2O emissions by up to 44% from sidedress-applied UAN, even though emission quantities varied by location and year due to differences in soil moisture, temperature, and precipitation. These latter variables plus soil NH4-N concentrations, in various combinations, accounted for 40 to 50% of the total variability associated with N2O emissions. These results can help inform UAN management decisions with regard to use of N stabilizers with UAN in the midwestern United States.
  • Authors:
    • Briggs, R.
    • Volk, T.
    • Pacaldo, R,
  • Source: BioEnergy Research
  • Volume: 6
  • Issue: 1
  • Year: 2013
  • Summary: Shrub willow biomass crops (SWBC) have been developed as a biomass feedstock for bioenergy, biofuels, and bioproducts in the northeastern and midwestern USA as well as in Europe. A previous life cycle analysis in North America showed that the SWBC production system is a low-carbon fuel source. However, this analysis is potentially inaccurate due to the limited belowground biomass data and the lack of aboveground stool biomass data. This study provides new information on the above- and belowground biomass, the carbon-nitrogen (C/N) ratio, and the root/shoot (R/S) ratio of willow biomass crops (Salix x dasyclados [SV1]), which have been in production from 5 to 19 years. The measured amounts of biomass were: 2.6 to 4.1 odt ha(-1) for foliage, 4.9 to 10.9 odt ha(-1) for aboveground stool (AGS), 2.9 to 5.7 odt ha(-1) for coarse roots (CR), 3.1 to 10.2 odt ha(-1) for belowground stool (BGS), and 5.6 to 9.9 odt ha(-1) for standing fine root (FR). The stem biomass production ranged from 7.0 to 18.0 odt ha(-1) year(-1) for the 5- and 19-year-old willows, respectively. C/N ratios ranged from 23 for foliage to 209 for belowground stool. An average R/S ratio of 2.0, calculated as total belowground biomass (BGS, CR, and FR) plus AGS divided by annual stem biomass, can be applied to estimate the total belowground biomass production of a mature SWBC. Based on AGS, BGS, and CR and standing FR biomass data, SWBC showed a net GHG potential of -42.9 Mg CO2 eq ha(-1) at the end of seven 3-year rotations.
  • Authors:
    • Kuzyakov, Y.
    • Zhu, B.
    • Pausch, J.
    • Cheng, W.
  • Source: Soil Biology & Biochemistry
  • Volume: 57
  • Year: 2013
  • Summary: Living roots and their hizodeposits can stimulate microbial activity and soil organic matter (SOM) decomposition up to several folds. This so-called rhizosphere priming effect (RPE) varies widely among plant species possibly due to species-specific differences in the quality and quantity of rhizodeposits and other root functions. However, whether the RPE is influenced by plant inter-species interactions remains largely unexplored, even though these interactions can fundamentally shape plant functions such as carbon allocation and nutrient uptake. In a 60-day greenhouse experiment, we continuously labeled monocultures and mixtures of sunflower, soybean and wheat with C-13-depleted CO2 and partitioned total CO2 efflux released from soil at two stages of plant development for SOM- and root-derived CO2. The RPE was calculated as the difference in SOM-derived CO2 between the planted and the unplanted soil, and was compared among the monocultures and mixtures. We found that the RPE was positive under all plants, ranging from 43% to 136% increase above the unplanted control. There were no significant differences in RPE at the vegetative stage. At the flowering stage however, the RPE in the soybean-wheat mixture was significantly higher than those in the sunflower monoculture, the sunflower-wheat mixture, and the sunflower-soybean mixture. These results indicated that the influence of plant inter-specific interactions on the RPE is case-specific and phenology-dependent. To evaluate the intensity of inter-specific effects on priming, we calculated an expected RPE for the mixtures based on the RPE of the monocultures weighted by their root biomass and compared it to the measured RPE under mixtures. At flowering, the measured RPE was significantly lower for the sunflower wheat mixture than what can be expected from their monocultures, suggesting that RPE was significantly reduced by the inter-species effects of sunflower and wheat. In summary, our results clearly demonstrated that inter-species interactions can significantly modify rhizosphere priming on SOM decomposition. (C) 2012 Elsevier Ltd. All rights reserved.
  • Authors:
    • Anex, R. P.
    • Parkin, T. B.
    • Fienen, M. N.
    • Rafique, R.
  • Source: Water, Air, & Soil Pollution
  • Volume: 224
  • Issue: 9
  • Year: 2013
  • Summary: DayCent is a biogeochemical model of intermediate complexity widely used to simulate greenhouse gases (GHG), soil organic carbon and nutrients in crop, grassland, forest and savannah ecosystems. Although this model has been applied to a wide range of ecosystems, it is still typically parameterized through a traditional "trial and error" approach and has not been calibrated using statistical inverse modelling (i.e. algorithmic parameter estimation). The aim of this study is to establish and demonstrate a procedure for calibration of DayCent to improve estimation of GHG emissions. We coupled DayCent with the parameter estimation (PEST) software for inverse modelling. The PEST software can be used for calibration through regularized inversion as well as model sensitivity and uncertainty analysis. The DayCent model was analysed and calibrated using N2O flux data collected over 2 years at the Iowa State University Agronomy and Agricultural Engineering Research Farms, Boone, IA. Crop year 2003 data were used for model calibration and 2004 data were used for validation. The optimization of DayCent model parameters using PEST significantly reduced model residuals relative to the default DayCent parameter values. Parameter estimation improved the model performance by reducing the sum of weighted squared residual difference between measured and modelled outputs by up to 67 %. For the calibration period, simulation with the default model parameter values underestimated mean daily N2O flux by 98 %. After parameter estimation, the model underestimated the mean daily fluxes by 35 %. During the validation period, the calibrated model reduced sum of weighted squared residuals by 20 % relative to the default simulation. Sensitivity analysis performed provides important insights into the model structure providing guidance for model improvement.
  • Authors:
    • Rotz, C. A.
    • Mauzerall, D. L.
    • Kanter, D.
    • Gehl, R. J.
    • Bruulsema, T. W.
    • Robertson, G. P.
    • Williams, C. O.
  • Source: Biogeochemistry
  • Volume: 114
  • Issue: 1-3
  • Year: 2013
  • Summary: Agriculture in the United States (US) cycles large quantities of nitrogen (N) to produce food, fuel, and fiber and is a major source of excess reactive nitrogen (Nr) in the environment. Nitrogen lost from cropping systems and animal operations moves to waterways, groundwater, and the atmosphere. Changes in climate and climate variability may further affect the ability of agricultural systems to conserve N. The N that escapes affects climate directly through the emissions of nitrous oxide (N2O), and indirectly through the loss of nitrate (NO3 (-)), nitrogen oxides (NO (x) ) and ammonia to downstream and downwind ecosystems that then emit some of the N received as N2O and NO (x) . Emissions of NO (x) lead to the formation of tropospheric ozone, a greenhouse gas that can also harm crops directly. There are many opportunities to mitigate the impact of agricultural N on climate and the impact of climate on agricultural N. Some are available today; many need further research; and all await effective incentives to become adopted. Research needs can be grouped into four major categories: (1) an improved understanding of agricultural N cycle responses to changing climate; (2) a systems-level understanding of important crop and animal systems sufficient to identify key interactions and feedbacks; (3) the further development and testing of quantitative models capable of predicting N-climate interactions with confidence across a wide variety of crop-soil-climate combinations; and (4) socioecological research to better understand the incentives necessary to achieve meaningful deployment of realistic solutions.