• Authors:
    • Desjardins, R. L.
    • McConkey, B. G.
    • Campbell, C. A.
    • Grant, B. B.
    • Smith, W. N.
    • Krobel, R.
    • Malhi, S. S.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 161
  • Year: 2012
  • Summary: Crop residues can be a viable source for biofuel production and other industrial products; however, their removal from agricultural land may negatively impact productivity and environmental quality. In this study three process-based models (CENTURY, DAYCENT, and DNDC) and the CAMPBELL empirical model were used to simulate soil organic carbon (SOC) change and were compared to observations from 14 residue removal experiments within the temperate climate areas of Canada and the Midwestern USA. The experimental results indicated that residue removal effects on SOC were more likely to be observed (i) with greater rates of residue removal, (ii) after longer periods, and (iii) with greater rates of (N) fertilizer. All four models simulated the hypothesized decline in SOC when residues were removed. The average measured SOC change for residue removal across all experimental sites and durations was -235 g m -2 (i.e., 3.3% of SOC in top 20 cm) whereas the SOC change as estimated by the models were -423, -417, -201, and -218 g m -2 for the CENTURY, DAYCENT, DNDC, and CAMPBELL models, respectively. All model predictions were close or within the range of uncertainty of estimates derived from measurements.
  • Authors:
    • Jackson, L. E.
    • O'Geen, A. T.
    • Smukler, S. M.
  • Source: Journal of Soil and Water Conservation
  • Volume: 67
  • Issue: 1
  • Year: 2012
  • Summary: The effectiveness of best management practices (BMPs) designed primarily to protect surface water quality was assessed on a farm certified for organic tomato production to consider potential environmental quality and production tradeoffs. The BMPs included winter cover crops typically used in organic farming to cycle nutrients and reduce stormwater runoff; tailwater ponds designed to capture runoff; and tailwater return systems, which recycle runoff back to the field. The study took place at a 44 ha (108 ac) farm in Yolo County, California, over a two-year period. Monitoring throughout the winter rainy season showed cover crops successfully reduced runoff and loads of several constituents during the storm events, when compared to fallow Total discharge was reduced by 44%, total suspended solids was reduced by 83%, ammonium was reduced by 33%, and dissolved organic carbon (DOC) was reduced by 58%. Estimates of leaching losses of DOC in the cover cropped fields, however, were 70% higher than the fallow fields in the winter rainy season and were 30% higher than the fallow fields in the summer irrigation season. During the summer irrigation season, the tailwater pond alone was highly effective in reducing losses of total suspended solids and volatile suspended solids to the neighboring riparian zone by 97% and 89%, respectively. The tailwater pond had no effect on dissolved reactive phosphorous and actually increased concentrations of nitrate-nitrogen (NO3--N) in effluent by 40% and DOC by 20%. As was expected, the NO3--N leaching measured by anion exchange resin bags and nitrous oxide emissions measured by static closed chambers was higher for the tailwater pond than the fallow field. Despite these differences, losses via NO3--N leaching and nitrous oxide emissions accounted for only 24.7 and 0.48 kg N ha(-1) y(-1) (22.0 and 0.40 lb N ac(-1)), respectively, for the entire farm, even including ponds and ditches. When field and plot values were extrapolated to the entire tomato production area to understand the relative potential tradeoffs, results indicate that BMPs could be implemented without an impact on tomato marketable yields; the tailwater pond's higher nitrous oxide emissions would not significantly increase the overall emissions for tomato production given its relatively small size; and using tailwater ponds in combination with cover crops would decrease total suspended solids (TSS) losses compared to cover crops alone, with only minor increases in NO3--N and DOC losses. Adding a tailwater return system to this combination of BMPs could help minimize these NO3--N and DOG losses. Use of cover crops with a tailwater pond and tailwater return system are a combination of BMPS that can thus be recommended for organic production when considering multiple environmental outcomes.
  • Authors:
    • Fixen, P. E.
    • Snyder, C. S.
  • Source: Journal of Soil and Water Conservation
  • Volume: 67
  • Issue: 5
  • Year: 2012
  • Authors:
    • Kanengieter, R. L.
    • Sleeter, R. R.
    • Bennett, S. L.
    • Reker, R. R.
    • Bouchard, M. A.
    • Sayler, K. L.
    • Sleeter, B. M.
    • Sohl, T. L.
    • Zhu, Z. L.
  • Source: AGRICULTURE ECOSYSTEMS & ENVIRONMENT
  • Volume: 153
  • Year: 2012
  • Summary: The Great Plains of the United States has undergone extensive land-use and land-cover change in the past 150 years, with much of the once vast native grasslands and wetlands converted to agricultural crops, and much of the unbroken prairie now heavily grazed. Future land-use change in the region could have dramatic impacts on ecological resources and processes. A scenario-based modeling framework is needed to support the analysis of potential land-use change in an uncertain future, and to mitigate potentially negative future impacts on ecosystem processes. We developed a scenario-based modeling framework to analyze potential future land-use change in the Great Plains. A unique scenario construction process, using an integrated modeling framework, historical data, workshops, and expert knowledge, was used to develop quantitative demand for future land-use change for four IPCC scenarios at the ecoregion level. The FORE-SCE model ingested the scenario information and produced spatially explicit land-use maps for the region at relatively fine spatial and thematic resolutions. Spatial modeling of the four scenarios provided spatial patterns of land-use change consistent with underlying assumptions and processes associated with each scenario. Economically oriented scenarios were characterized by significant loss of natural land covers and expansion of agricultural and urban land uses. Environmentally oriented scenarios experienced modest declines in natural land covers to slight increases. Model results were assessed for quantity and allocation disagreement between each scenario pair. In conjunction with the U.S. Geological Survey's Biological Carbon Sequestration project, the scenario-based modeling framework used for the Great Plains is now being applied to the entire United States.
  • Authors:
    • McAloon, A. J.
    • Lamb, M. C.
    • Lima, I. M.
    • Boateng, A. A.
    • Collins, H. P.
    • Ippolito, J. A.
    • Archer, D. W.
    • Novak, J. M.
    • Cantrell, K. B.
    • Spokas, K. A.
    • Lentz, R. D.
    • Nichols, K. A.
  • Source: Journal of Environmental Quality
  • Volume: 41
  • Issue: 4
  • Year: 2012
  • Summary: Biochar has been heralded as an amendment to revitalize degraded soils, improve soil carbon sequestration, increase agronomic productivity, and enter into future carbon trading markets. However, scientific and economic technicalities may limit the ability of biochar to consistently deliver on these expectations. Past research has demonstrated that biochar is part of the black carbon continuum with variable properties due to the net result of production (e.g., feedstock and pyrolysis conditions) and postproduction factors (storage or activation). Therefore, biochar is not a single entity but rather spans a wide range of black carbon forms. Biochar is black carbon, but not all black carbon is biochar. Agronomic benefits arising from biochar additions to degraded soils have been emphasized, but negligible and negative agronomic effects have also been reported. Fifty percent of the reviewed studies reported yield increases after black carbon or biochar additions, with the remainder of the studies reporting alarming decreases to no significant differences. Hardwood biochar (black carbon) produced by traditional methods (kilns or soil pits) possessed the most consistent yield increases when added to soils. The universality of this conclusion requires further evaluation due to the highly skewed feedstock preferences within existing studies. With global population expanding while the amount of arable land remains limited, restoring soil quality to nonproductive soils could be key to meeting future global food production, food security, and energy supplies; biochar may play a role in this endeavor. Biochar economics are often marginally viable and are tightly tied to the assumed duration of agronomic benefits. Further research is needed to determine the conditions under which biochar can provide economic and agronomic benefits and to elucidate the fundamental mechanisms responsible for these benefits.
  • Authors:
    • Stockwell, R.
    • Bitan, E.
  • Source: Journal of Soil and Water Conservation
  • Volume: 67
  • Issue: 3
  • Year: 2012
  • Authors:
    • Cavigelli, M. A.
    • Spargo, J. T.
    • Mirsky, S. B.
    • Teasdale, J. R.
    • Maul, J. E.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 3
  • Year: 2012
  • Summary: There is interest in developing no-tillage systems for organic farming; however, potential limitations include the inability to control weeds and to provide sufficient crop available N. A 3-yr field experiment was conducted on organically certified land to explore roller-crimper technology for terminating a hairy vetch ( Vicia villosa Roth) cover crop in a reduced-tillage compared to a disk-tillage organic corn ( Zea mays L.) production system in Maryland. Within this tillage comparison, factors including the corn planting date and post-plant cultivation were examined for optimizing reduced-tillage organic corn production. Corn yield in roll-killed hairy vetch treatments where corn was planted by mid-June and that received high-residue cultivation was similar or higher than the best treatments with disk-killed hairy vetch. Delayed corn planting dates had little impact on corn yield in either disk- or roll-killed treatments, a result consistent with the similarity in weed biomass after cultivation, fertility, moisture, and radiation across planting dates. In 2 yr with supplemented weed populations, weed biomass was the major driver determining corn yield, which was reduced by 53 to 68% relative to weed-free control plots in the absence of post-plant cultivation, and by 21 to 28% with post-plant cultivation. In a year with low, natural weed populations, weeds had no significant influence on yield. These results demonstrate that organic corn production in a reduced-tillage roll-killed cover crop system can provide similar yields to those in a traditional tillage-based system, but also highlight the importance of maintaining low weed populations to optimize corn yield.
  • 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:
    • Williams, C.
    • Walling, S.
    • Sample, D.
    • Radloff, G.
    • Jackson, R.
    • Hull, S.
    • Ventura, S.
  • Source: Journal of Soil and Water Conservation
  • Volume: 67
  • Issue: 1
  • Year: 2012
  • Authors:
    • Ingram, K. T.
    • Jones, J. W.
    • Woli, P.
    • Fraisse, C. W.
  • Source: AGRONOMY JOURNAL
  • Volume: 104
  • Issue: 2
  • Year: 2012
  • Summary: Several drought indices are available to compute the degree of drought to which crops are exposed. They vary in complexity, generality, and the adequacy with which they represent processes in the soil, plant, and atmosphere. Agricultural Reference Index for Drought (ARID) was developed as a reference index to approximate the water stress factor that is used to affect growth and other physiological processes in crop simulation models. Using RMSE, Willmott d index, and modeling efficiency (ME) as performance measures, ARID was evaluated using soil water contents in the root zone measured daily in two grass fields in Florida. The ability of ARID was assessed through comparison with the water deficit index (WSPD) of the Decision Support System for Agrotechnology Transfer (DSSAT) CERES-Maize model. Seven other drought indices were compared with WSPD to identify the most appropriate agricultural drought index. Values of each index were computed for full canopy cover periods of maize ( Zea mays L.) crops for 16 locations in the U.S. Southeast. Using periodic values, the performance of each index was assessed in terms of its correlation ( r) with and departure from WSPD. The ARID reasonably predicted soil water contents (RMSE=0.01-0.019, d index=0.92-0.94, ME=0.66-0.73) and adequately approximated WSPD ( r=0.90, RMSE=0.15). Among the indices compared, ARID mimicked WSPD the most closely (RMSE smaller by 1-83%, r larger by 1-630%) and captured weather fluctuation effects the most accurately. Results indicated that ARID may be used as a simple index for quantifying drought and its effects on crop yields.