• Authors:
    • Rubenstein, D.
    • Notenbaert, A.
    • Beringer, T.
    • Thornton, P. K.
    • Estes, L.
    • Searchinger, T. D.
    • Heimlich, R.
    • Licker, R.
    • Herrero, M.
  • Source: Article
  • Volume: 5
  • Issue: 5
  • Year: 2015
  • Summary: Do the wet savannahs and shrublands of Africa provide a large reserve of potential croplands to produce food staples or bioenergy with low carbon and biodiversity costs? We find that only small percentages of these lands have meaningful potential to be low-carbon sources of maize (1/42%) or soybeans (9.5-11.5%), meaning that their conversion would release at least one-third less carbon per ton of crop than released on average for the production of those crops on existing croplands. Factoring in land-use change, less than 1% is likely to produce cellulosic ethanol that would meet European standards for greenhouse gas reductions. Biodiversity effects of converting these lands are also likely to be significant as bird and mammal richness is comparable to that of the world's tropical forest regions. Our findings contrast with influential studies that assume these lands provide a large, low-environmental-cost cropland reserve. © 2015 Macmillan Publishers Limited. All rights reserved.
  • Authors:
    • Vicca, S.
    • Davidson, E.
    • Trumbore, S.
    • Sierra, C.
    • Janssens,I.
  • Source: Journal of Advances in Modeling Earth Systems
  • Volume: 7
  • Issue: 1
  • Year: 2015
  • Summary: The sensitivity of soil organic matter decomposition to global environmental change is a topic of prominent relevance for the global carbon cycle. Decomposition depends on multiple factors that are being altered simultaneously as a result of global environmental change; therefore, it is important to study the sensitivity of the rates of soil organic matter decomposition with respect to multiple and interacting drivers. In this manuscript, we present an analysis of the potential response of decomposition rates to simultaneous changes in temperature and moisture. To address this problem, we first present a theoretical framework to study the sensitivity of soil organic matter decomposition when multiple driving factors change simultaneously. We then apply this framework to models and data at different levels of abstraction: (1) to a mechanistic model that addresses the limitation of enzyme activity by simultaneous effects of temperature and soil water content, the latter controlling substrate supply and oxygen concentration for microbial activity; (2) to different mathematical functions used to represent temperature and moisture effects on decomposition in biogeochemical models. To contrast model predictions at these two levels of organization, we compiled different data sets of observed responses in field and laboratory studies. Then we applied our conceptual framework to: (3) observations of heterotrophic respiration at the ecosystem level; (4) laboratory experiments looking at the response of heterotrophic respiration to independent changes in moisture and temperature; and (5) ecosystem-level experiments manipulating soil temperature and water content simultaneously.
  • Authors:
    • Helmers, M. J.
    • Kostel, J. A.
    • James, D. E.
    • Boomer, K. M. B.
    • Porter, S. A.
    • Tomer, M. D.
    • Isenhart, T. M.
    • McLellan, E.
  • Source: Agronomy Journal
  • Volume: 44
  • Issue: 3
  • Year: 2015
  • Summary: Spatial data on soils, land use, and topography, combined with knowledge of conservation effectiveness, can be used to identify alternatives to reduce nutrient discharge from small (hydrologic unit code [HUC]12) watersheds. Databases comprising soil attributes, agricultural land use, and light detection and ranging-derived elevation models were developed for two glaciated midwestern HUC12 watersheds: Iowa's Beaver Creek watershed has an older dissected landscape, and Lime Creek in Illinois is young and less dissected. Subsurface drainage is common in both watersheds. We identified locations for conservation practices, including in-field practices (grassed waterways), edge-of-field practices (nutrient-removal wetlands, saturated buffers), and drainage-water management, by applying terrain analyses, geographic criteria, and cross-classifications to field- and watershed-scale geographic data. Cover crops were randomly distributed to fields without geographic prioritization. A set of alternative planning scenarios was developed to represent a variety of extents of implementation among these practices. The scenarios were assessed for nutrient reduction potential using a spreadsheet approach to calculate the average nutrient-removal efficiency required among the practices included in each scenario to achieve a 40% NO 3-N reduction. Results were evaluated in the context of the Iowa Nutrient Reduction Strategy, which reviewed nutrient-removal efficiencies of practices and established the 40% NO 3-N reduction as Iowa's target for Gulf of Mexico hypoxia mitigation by agriculture. In both test watersheds, planning scenarios that could potentially achieve the targeted NO 3-N reduction but remove <5% of cropland from production were identified. Cover crops and nutrient removal wetlands were common to these scenarios. This approach provides an interim technology to assist local watershed planning and could provide planning scenarios to evaluate using watershed simulation models. A set of ArcGIS tools is being released to enable transfer of this mapping technology.
  • Authors:
    • Kohmann, M. M.
    • Torres, C. M. M. E.
    • Fraisse, C. W.
  • Source: Agricultural Journal
  • Volume: 137
  • Year: 2015
  • Summary: Agriculture is an important source of greenhouse gases (GHG), especially from crop production practices and enteric fermentation by ruminant livestock. Improved production practices in agriculture and increase in terrestrial carbon sinks are alternatives for mitigating GHG emissions in agriculture. The objective of this study was to estimate GHG emissions from hypothetical farm enterprise combinations in the southeastern United States with a mix of cropland and livestock production and estimate the area of forest plantation necessary to offset these emissions. Four different farm enterprise combinations (Cotton; Maize; Peanut; Wheat + Livestock + Forest) with different production practices were considered in the study resulting in different emission scenarios. We assumed typical production practices of farm operations in the region with 100 ha of cropland area and a herd of 50 cows. GHG emissions were calculated regarding production, storage and transportation of agrochemicals (pre-farm) and farm activities such as fertilization, machinery operation and irrigation (on-farm). Simulated total farm GHG emissions for the different farm enterprise combinations and production practices ranged from 348.8 t CO2e year-1 to 765.6 t CO2e year-1. The estimated forest area required to neutralize these emissions ranged from 19 ha to 40 ha. In general, enterprise combinations with more intense production practices that include the use of irrigation resulted in higher total emissions but lower emissions per unit of commodity produced. © 2015 Elsevier Ltd.
  • Authors:
    • Shonnard, D.
    • Archer, D.
    • Beck, E.
    • Ukaew, S.
  • Source: Journal
  • Volume: 20
  • Issue: 5
  • Year: 2015
  • Summary: Rapeseed is being considered as a potential feedstock for hydrotreated renewable jet (HRJ) fuel in the USA through its cultivation in rotation with wheat. The goal of this research was to determine the impact of soil C changes, induced through replacing the fallow period with rapeseed in rotation with wheat, and the effects it would have on emission of greenhouse gases (GHG) of rapeseed HRJ. The Intergovernmental Panel on Climate Change (IPCC) (Tier 1) method was used with modifications to determine the changes in soil C of wheat-wheat-rapeseed (WWR) relative to the reference wheat-wheat-fallow (WWF) rotation for 20 years of cultivation. The 27 case scenarios were conducted to study the impacts of changes in management practices (tillage practice and residue input) on changes in soil C for WWR rotation in multiple locations in 10 US states. The CO2 emissions resulting from soil C changes were incorporated into the rapeseed HRJ pathway in order to evaluate the GHG emissions. Introducing rapeseed to replace the fallow period with wheat could either increase or decrease changes in soil C, depending on management practices. Soil C is predicted to increase with increased residue input and reduced tillage. The greatest gain of soil C was found when using high residue input for wheat and rapeseed under no tillage, resulting in the best management practice. Conversely, adding low residue input to both crops with full tillage created the highest loss of soil C, referring to as the worst management practice. Soil C changes varied across locations from -0.22 to 0.32 Mg C ha(-1) year(-1). Consequently, the GHG emissions of rapeseed HRJ ranged from 4 to 70 g CO2 eq./MJ, comparing to 46 g CO2 eq./MJ for excluding soil C change. The rapeseed HRJ exhibited the GHG savings of 65-96 % for the best practice and 20-42 % for the worst practice when compared to petroleum jet fuel. Based on results using the modified IPCC method, adoption of high residue input with no tillage for the rotation cropping of rapeseed with wheat had the potential to increase soil C. However, the method has limitations for predicting soil C changes regarding crop management practices. Biogeochemical-based models that have a potential to capture processes of C and N dynamics in soil and yield may be better suited to quantify regional variations in soil C changes for the rotation cropping of rapeseed with wheat.
  • Authors:
    • Lobell, D.
    • Schlenker, W.
    • Roberts, M.
    • Urban, D.
  • Source: Journal
  • Volume: 130
  • Issue: 2
  • Year: 2015
  • Summary: Short durations of very high spring soil moisture can influence crop yields in many ways, including delaying planting and damaging young crops. The central United States has seen a significant upward trend in the frequency and intensity of extreme precipitation in the 20th century, potentially leading to more frequent occurrences of saturated or nearly saturated fields during the planting season, yet the impacts of these changes on crop yields are not known. Here we investigate the yield response to excess spring moisture for both maize and soybean in the U.S. states of Illinois, Iowa, and Indiana, and the impacts of historical trends for 1950-2011. We find that simple measures of extreme spring soil moisture, derived from fine-scale daily moisture data from the Variable Infiltration Capacity (VIC) hydrologic model, lead to significant improvements in statistical models of yields for both crops. Individual counties experience up to 10 % loss in years with extremely wet springs. However, losses due to historical trends in excess spring moisture measures have generally been small, with 1-3 % yield loss over the 62 year study period.
  • Authors:
    • Lobell, D.
    • Abelleyra, D.
    • Veron, S.
  • Source: Article
  • Volume: 130
  • Issue: 2
  • Year: 2015
  • Summary: Understanding regional impacts of recent climate trends can help anticipate how further climate change will affect agricultural productivity. We here used panel models to estimate the contribution of growing season precipitation (P), average temperature (T) and diurnal temperature range (DTR) on wheat, maize and soy yield and yield trends between 1971 and 2012 from 33 counties of the Argentine Pampas. A parallel analysis was conducted on a per county basis by adjusting a linear model to the first difference (i.e., subtracting from each value the previous year value) in yield and first difference in weather variables to estimate crop sensitivity to interannual changes in P, T, and DTR. Our results show a relatively small but significant negative impact of climate trends on yield which is consistent with the estimated crop and county specific sensitivity of yield to interannual changes in P, T and DTR and their temporal trends. Median yield loss from climate trends for the 1971-2012 period amounted to 5.4 % of average yields for maize, 5.1 % for wheat, and 2.6 % for soy. Crop yield gains for this time period could have been 15-20 % higher if climate remained without directional changes in the Pampas. On average, crop yield responded more to trends in T and DTR than in P. Translated into economic terms the observed reductions in maize, wheat, and soy yields due to climate trends in the Pampas would equal $1.1 B using 2013 producer prices. These results add to the increasing evidence that climate trends are slowing yield increase.
  • Authors:
    • Lynch, J. P.
    • Zhan, A.
  • Source: Article
  • Volume: 66
  • Issue: 7
  • Year: 2015
  • Summary: Suboptimal nitrogen (N) availability is a primary constraint for crop production in developing countries, while in developed countries, intensive N fertilization is a primary economic, energy, and environmental cost for crop production. We tested the hypothesis that under low-N conditions, maize ( Zea mays) lines with few but long (FL) lateral roots would have greater axial root elongation, deeper rooting, and greater N acquisition than lines with many but short (MS) lateral roots. Maize recombinant inbred lines contrasting in lateral root number and length were grown with adequate and suboptimal N in greenhouse mesocosms and in the field in the USA and South Africa (SA). In low-N mesocosms, the FLphenotype had substantially reduced root respiration and greater rooting depth than the MS phenotype. In low-N fields in the USA and SA, the FLphenotype had greater rooting depth, shoot N content, leaf photosynthesis, and shoot biomass than the MS phenotype. The FLphenotype yielded 31.5% more than the MS phenotype under low N in the USA. Our results are consistent with the hypothesis that sparse but long lateral roots improve N capture from low-N soils. These results with maize probably pertain to other species. The FLlateral root phenotype merits consideration as a selection target for greater crop N efficiency.
  • Authors:
    • Wang, E.
    • Luo, Z.
    • King, D.
    • Bryan, B. A.
    • Zhao, G.
    • Yu, Q.
  • Source: GCB Bioenergy
  • Volume: 7
  • Issue: 3
  • Year: 2015
  • Summary: The use of crop residues for bioenergy production needs to be carefully assessed because of the potential negative impact on the level of soil organic carbon (SOC) stocks. The impact varies with environmental conditions and crop management practices and needs to be considered when harvesting the residue for bioenergy productions. Here, we defined the sustainable harvest limits as the maximum rates that do not diminish SOC and quantified sustainable harvest limits for wheat residue across Australia's agricultural lands. We divided the study area into 9432 climate-soil (CS) units and simulated the dynamics of SOC in a continuous wheat cropping system over 122years (1889 - 2010) using the Agricultural Production Systems sIMulator (APSIM). We simulated management practices including six fertilization rates (0, 25, 50, 75, 100, and 200kg Nha(-1)) and five residue harvest rates (0, 25, 50, 75, and 100%). We mapped the sustainable limits for each fertilization rate and assessed the effects of fertilization and three key environmental variables - initial SOC, temperature, and precipitation - on sustainable residue harvest rates. We found that, with up to 75kg Nha(-1) fertilization, up to 75% and 50% of crop residue could be sustainably harvested in south-western and south-eastern Australia, respectively. Higher fertilization rates achieved little further increase in sustainable residue harvest rates. Sustainable residue harvest rates were principally determined by climate and soil conditions, especially the initial SOC content and temperature. We conclude that environmental conditions and management practices should be considered to guide the harvest of crop residue for bioenergy production and thereby reduce greenhouse gas emissions during the life cycle of bioenergy production.
  • Authors:
    • Grosso, S. J.
    • Spatari, S.
    • Pourhashem, G.
    • Mitchell, J. G.
    • Adler, P. R.
    • Parton, W. J.
  • Source: Research Article
  • Volume: 25
  • Issue: 4
  • Year: 2015
  • Summary: Crop residues are potentially significant sources of feedstock for biofuel production in the United States. However, there are concerns with maintaining the environmental functions of these residues while also serving as a feedstock for biofuel production. Maintaining soil organic carbon (SOC) along with its functional benefits is considered a greater constraint than maintaining soil erosion losses to an acceptable level. We used the biogeochemical model DayCent to evaluate the effect of residue removal, corn stover, and wheat and barley straw in three diverse locations in the USA. We evaluated residue removal with and without N replacement, along with application of a high-lignin fermentation byproduct (HLFB), the residue by-product comprised of lignin and small quantities of nutrients from cellulosic ethanol production. SOC always decreased with residue harvest, but the decrease was greater in colder climates when expressed on a life cycle basis. The effect of residue harvest on soil N 2O emissions varied with N addition and climate. With N addition, N 2O emissions always increased, but the increase was greater in colder climates. Without N addition, N 2O emissions increased in Iowa, but decreased in Maryland and North Carolina with crop residue harvest. Although SOC was lower with residue harvest when HLFB was used for power production instead of being applied to land, the avoidance of fossil fuel emissions to the atmosphere by utilizing the cellulose and hemicellulose fractions of crop residue to produce ethanol (offsets) reduced the overall greenhouse gas (GHG) emissions because most of this residue carbon would normally be lost during microbial respiration. Losses of SOC and reduced N mineralization could both be mitigated with the application of HLFB to the land. Therefore, by returning the high-lignin fraction of crop residue to the land after production of ethanol at the biorefinery, soil carbon levels could be maintained along with the functional benefit of increased mineralized N, and more GHG emissions could be offset compared to leaving the crop residues on the land.