• Authors:
    • Pijanowski, B. C.
    • Plourde, J. D.
    • Pekin, B. K.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 165
  • Year: 2013
  • Summary: While crop rotation patterns can be complex with multiple crops rotated over several years, the most common rotation practice in the Central United States is biannual rotation between corn and soybeans. We analyzed the changes in crop rotation patterns from 2003 to 2010 using the Cropland Data Layer (CDL), which provides remotely sensed land cover layers for agricultural crops in the Central United States. The accuracy of the CDL was validated by comparing the total acreage for a state or county present in the CDL with the total planted crop acreage available from the National Agricultural Statistics Service. The data layers were combined into two time periods 2003-2006 and 2007-2010, and specific rotation patterns were determined for every location in the study area. The combinations resulted in unique sequences such as single, double, triple and quadruple, the latter of which is equivalent to the same crop class present all four years at a particular location. Corn and soybeans were analyzed to determine the amount of area used for production as well as the amount of change between unique crop rotation sequences. While the total area under production of major crops in the second half of our study period increased only slightly, the extent to which major crops (e.g., corn and soybeans) were grown in continuous cropping sequences increased significantly. For example, the amount of land impacted by corn in the first time period increased by only 2% in the second time period. However, the amount of corn grown in quadruple sequence doubled from the first half to the second half of our study period. We conclude that, although crop rotation patterns are very complex in this region, involving considerable amount of non-cropland, the footprint of major crops such as corn have moved toward monoculture cropping practices in the last decade.
  • Authors:
    • Prokopy, L. S.
    • Gramig, B. M.
    • Reimer, A. P.
  • Source: Journal of Soil and Water Conservation
  • Volume: 68
  • Issue: 2
  • Year: 2013
  • Summary: Despite its economic and social benefits, agriculture is now a leading source of water pollution in the United States. While significant research effort has attempted to understand adoption of conservation practices on agricultural lands, relatively little research has explored the operation of specific agri-environmental policies in the United States. This research attempts to gain an understanding of how differing agricultural and sociopolitical contexts across the United States influence attempted participation in national agricultural conservation programs. Application rates in the Environmental Quality Incentives Program (EQIP) differ across the 50 states, indicating potentially important differences in state setting that influence behavior of individual farm operators. A variety of agricultural and sociopolitical measures were included in a fractional logit model to assess factors contributing to varying rates of application to EQIP. Significant explanatory variables included high sales farm prevalence, tenancy rates, and views on federal environmental spending. There also appears to be a large regional effect, with states in the Southeast, Mountain West, and Northeast having higher application rates than those in the Corn Belt. The results of this analysis indicate that certain types of farmers are more likely to seek participation in this large agricultural conservation program. Further research is needed to assess the role of government agencies (federal, state, and local) in influencing participation rates and what role individual political opinion may play in decisions related to federal cost share programs.
  • Authors:
    • Uliasz, M.
    • Richardson, S.
    • Miles, N.
    • Davis, K. J.
    • Denning, A. S.
    • West, T. O.
    • Lauvaux, T.
    • Schuh, A. E.
    • Lokupitiya, E.
    • Cooley, D.
    • Andrews, A.
    • Ogle, S.
  • Source: Global Change Biology
  • Volume: 19
  • Issue: 5
  • Year: 2013
  • Summary: An intensive regional research campaign was conducted by the North American Carbon Program (NACP) in 2007 to study the carbon cycle of the highly productive agricultural regions of the Midwestern United States. Forty-five different associated projects were conducted across five US agencies over the course of nearly a decade involving hundreds of researchers. One of the primary objectives of the intensive campaign was to investigate the ability of atmospheric inversion techniques to use highly calibrated CO 2 mixing ratio data to estimate CO 2 flux over the major croplands of the United States by comparing the results to an inventory of CO 2 fluxes. Statistics from densely monitored crop production, consisting primarily of corn and soybeans, provided the backbone of a well studied bottom-up inventory flux estimate that was used to evaluate the atmospheric inversion results. Estimates were compared to the inventory from three different inversion systems, representing spatial scales varying from high resolution mesoscale (PSU), to continental (CSU) and global (CarbonTracker), coupled to different transport models and optimization techniques. The inversion-based mean CO 2-C sink estimates were generally slightly larger, 8-20% for PSU, 10-20% for CSU, and 21% for CarbonTracker, but statistically indistinguishable, from the inventory estimate of 135 TgC. While the comparisons show that the MCI region-wide C sink is robust across inversion system and spatial scale, only the continental and mesoscale inversions were able to reproduce the spatial patterns within the region. In general, the results demonstrate that inversions can recover CO 2 fluxes at sub-regional scales with a relatively high density of CO 2 observations and adequate information on atmospheric transport in the region.
  • Authors:
    • Anderson-Teixeira, K. J.
    • Masters, M. D.
    • Mitchell, C. A.
    • David, M. B.
    • Smith, C. M.
    • Bernacchi, C. J.
    • DeLucia, E. H.
  • Source: Journal of Environmental Quality
  • Volume: 42
  • Issue: 1
  • Year: 2013
  • Summary: Current biofuel feedstock crops such as corn lead to large environmental losses of N through nitrate leaching and N 2O emissions; second-generation cellulosic crops have the potential to reduce these N losses. We measured N losses and cycling in establishing miscanthus ( Miscanthus * giganteus), switchgrass ( Panicum virgatum L. fertilized with 56 kg N ha -1 yr -1), and mixed prairie, along with a corn ( Zea mays L.)-corn-soybean [ Glycine max (L.) Merr.] rotation (corn fertilized at 168-202 kg N ha -1). Nitrous oxide emissions, soil N mineralization, mid-profile nitrate leaching, and tile flow and nitrate concentrations were measured. Perennial crops quickly reduced nitrate leaching at a 50-cm soil depth as well as concentrations and loads from the tile systems (year 1 tile nitrate concentrations of 10-15 mg N L -1 declined significantly by year 4 in all perennial crops to <0.6 mg N L -1, with losses of <0.8 kg N ha -1 yr -1). Nitrous oxide emissions were 2.2 to 7.7 kg N ha -1 yr -1 in the corn-corn-soybean rotation but were <1.0 kg N ha -1 yr -1 by year 4 in the perennial crops. Overall N balances (atmospheric deposition+fertilization+soybean N 2 fixation-harvest, leaching losses, and N 2O emissions) were positive for corn and soybean (22 kg N ha -1 yr -1) as well as switchgrass (9.7 kg N ha -1 yr -1) but were -18 and -29 kg N ha -1 yr -1 for prairie and miscanthus, respectively. Our results demonstrate rapid tightening of the N cycle as perennial biofuel crops established on a rich Mollisol soil.
  • Authors:
    • Smith, N. G.
    • Dukes, J. S.
  • Source: Global Change Biology
  • Volume: 19
  • Issue: 1
  • Year: 2013
  • Summary: To realistically simulate climate feedbacks from the land surface to the atmosphere, models must replicate the responses of plants to environmental changes. Several processes, operating at various scales, cause the responses of photosynthesis and plant respiration to temperature and CO 2 to change over time of exposure to new or changing environmental conditions. Here, we review the latest empirical evidence that short-term responses of plant carbon exchange rates to temperature and CO 2 are modified by plant photosynthetic and respiratory acclimation as well as biogeochemical feedbacks. We assess the frequency with which these responses have been incorporated into vegetation models, and highlight recently designed algorithms that can facilitate their incorporation. Few models currently include representations of the long-term plant responses that have been recorded by empirical studies, likely because these responses are still poorly understood at scales relevant for models. Studies show that, at a regional scale, simulated carbon flux between the atmosphere and vegetation can dramatically differ between versions of models that do and do not include acclimation. However, the realism of these results is difficult to evaluate, as algorithm development is still in an early stage, and a limited number of data are available. We provide a series of recommendations that suggest how a combination of empirical and modeling studies can produce mechanistic algorithms that will realistically simulate longer term responses within global-scale models.
  • Authors:
    • Lehmann, J.
    • Lal, R.
    • Jastrow, J. D.
    • Chenu, C.
    • Brookes, P. C.
    • Bird, M.
    • Baldock, J.
    • Angers, D. A.
    • Abbott, L.
    • Wheeler, I.
    • Singh, K.
    • Courcelles, V. de R. de
    • McBratney, A. B.
    • Minasny, B.
    • Jenkins, M.
    • Henakaarchchi, N.
    • Field, D. J.
    • Crawford, J. W.
    • Adams, M. A.
    • Stockmann, U.
    • O'Donnell, A. G.
    • Parton, W. J.
    • Whitehead, D.
    • Zimmermann, M.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 164
  • Year: 2013
  • Summary: Soil contains approximately 2344 Gt (1 gigaton=1 billion tonnes) of organic carbon globally and is the largest terrestrial pool of organic carbon. Small changes in the soil organic carbon stock could result in significant impacts on the atmospheric carbon concentration. The fluxes of soil organic carbon vary in response to a host of potential environmental and anthropogenic driving factors. Scientists worldwide are contemplating questions such as: 'What is the average net change in soil organic carbon due to environmental conditions or management practices?', 'How can soil organic carbon sequestration be enhanced to achieve some mitigation of atmospheric carbon dioxide?' and 'Will this secure soil quality?'. These questions are far reaching, because maintaining and improving the world's soil resource is imperative to providing sufficient food and fibre to a growing population. Additional challenges are expected through climate change and its potential to increase food shortages. This review highlights knowledge of the amount of carbon stored in soils globally, and the potential for carbon sequestration in soil. It also discusses successful methods and models used to determine and estimate carbon pools and fluxes. This knowledge and technology underpins decisions to protect the soil resource.
  • Authors:
    • Brown, D. G.
    • Sylvester, K. M.
    • Deane, G. D.
    • Kornak, R. N.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 168
  • Year: 2013
  • Summary: This paper examines drivers of land-cover change in the U.S. Great Plains in the last half of the twentieth century. Its central aim is to evaluate the dynamics of grassland preservation and conversion, across the region, and to identify areas of grassland that were never plowed during the period. The research compares land-cover data from 400 sample areas, selected from and nested within 50 counties, to aggregate data from the agricultural and population censuses. The spatially explicit land-cover data were interpreted from aerial photographs taken at three time points (1950s, 1970s and 2000s). Sample areas were chosen using a stratified random design based on the Public Land Survey grid with in the target counties, in several clusters across the region. We modeled the sequences and magnitudes of changes in the interpreted air photo data in a multi-level panel model that included soil quality and slope of sample areas and agricultural activities and employment reported in the U.S. Censuses of Agriculture and Population. We conclude that land retirement programs and production subsidies have worked at cross purposes, destabilizing micro-level patterns of land use in recent decades, increasing levels of switching between cropland and grassland and reducing the size of remaining areas of native grassland in the U.S. Great Plains.
  • Authors:
    • Pendall, E.
    • Bell, J.
    • Tucker, C. L.
    • Ogle, K.
  • Source: Global Change Biology
  • Volume: 19
  • Issue: 1
  • Year: 2013
  • Summary: Enhanced soil respiration in response to global warming may substantially increase atmospheric CO 2 concentrations above the anthropogenic contribution, depending on the mechanisms underlying the temperature sensitivity of soil respiration. Here, we compared short-term and seasonal responses of soil respiration to a shifting thermal environment and variable substrate availability via laboratory incubations. To analyze the data from incubations, we implemented a novel process-based model of soil respiration in a hierarchical Bayesian framework. Our process model combined a Michaelis-Menten-type equation of substrate availability and microbial biomass with an Arrhenius-type nonlinear temperature response function. We tested the competing hypotheses that apparent thermal acclimation of soil respiration can be explained by depletion of labile substrates in warmed soils, or that physiological acclimation reduces respiration rates. We demonstrated that short-term apparent acclimation can be induced by substrate depletion, but that decreasing microbial biomass carbon (MBC) is also important, and lower MBC at warmer temperatures is likely due to decreased carbon-use efficiency (CUE). Observed seasonal acclimation of soil respiration was associated with higher CUE and lower basal respiration for summer- vs. winter-collected soils. Whether the observed short-term decrease in CUE or the seasonal acclimation of CUE with increased temperatures dominates the response to long-term warming will have important consequences for soil organic carbon storage.
  • Authors:
    • McConnaughay, K. D.
    • Bernacchi, C. J.
    • Richter, K. T.
    • Bryant, J. J.
    • Twine, T. E.
    • Morris, S. J.
    • Leakey, A. D. B.
  • Source: Global Change Biology
  • Volume: 19
  • Issue: 9
  • Year: 2013
  • Summary: The physiological response of vegetation to increasing atmospheric carbon dioxide concentration ([CO 2]) modifies productivity and surface energy and water fluxes. Quantifying this response is required for assessments of future climate change. Many global climate models account for this response; however, significant uncertainty remains in model simulations of this vegetation response and its impacts. Data from in situ field experiments provide evidence that previous modeling studies may have overestimated the increase in productivity at elevated [CO 2], and the impact on large-scale water cycling is largely unknown. We parameterized the Agro-IBIS dynamic global vegetation model with observations from the SoyFACE experiment to simulate the response of soybean and maize to an increase in [CO 2] from 375 ppm to 550 ppm. The two key model parameters that were found to vary with [CO 2] were the maximum carboxylation rate of photosynthesis and specific leaf area. Tests of the model that used SoyFACE parameter values showed a good fit to site-level data for all variables except latent heat flux over soybean and sensible heat flux over both crops. Simulations driven with historic climate data over the central USA showed that increased [CO 2] resulted in decreased latent heat flux and increased sensible heat flux from both crops when averaged over 30 years. Thirty-year average soybean yield increased everywhere (ca. 10%); however, there was no increase in maize yield except during dry years. Without accounting for CO 2 effects on the maximum carboxylation rate of photosynthesis and specific leaf area, soybean simulations at 550 ppm overestimated leaf area and yield. Our results highlight important model parameter values that, if not modified in other models, could result in biases when projecting future crop-climate-water relationships.
  • Authors:
    • McCoy, T. D.
    • Guan, Q. F.
    • Mitchell, R. B.
    • Allen, C. R.
    • Uden, D. R.
  • Source: Journal of Soil and Water Conservation
  • Volume: 68
  • Issue: 5
  • Year: 2013