• Authors:
    • Balkcom, K. S.
    • Gamble, B. E.
    • Patterson, M. G.
    • Reeves, D. W.
    • Price, A. J.
    • Arriaga, F. J.
    • Monks, C. D.
  • Source: Peanut Science
  • Volume: 34
  • Issue: 1
  • Year: 2007
  • Summary: Information is needed on the role of cover crops as a weed control alternative due to the increase in adoption of conservation-tillage in peanut production. Field experiments were conducted from autumn 1994 through autumn 1997 in Alabama to evaluate three winter cereal cover crops in a high-residue conservation-tillage peanut production system. Black oat ( Avena strigosa Schreb.), rye ( Secale cereale L.), and wheat ( Triticum aestivum L.) were evaluated for their weed-suppressive characteristics compared to a winter fallow system. Three herbicide systems were utilized: no herbicide, preemergence (PRE) herbicides followed by (fb) postemergence (POST) herbicides, and PRE fb sequential POST herbicides. The PRE fb POST herbicide input system consisted of pendimethalin at 1.12 kg ai/ha fb an additional early POST application of paraquat at 0.14 kg ai/ha plus bentazon at 0.56 kg ai/ha. The PRE fb sequential POST herbicide input system contained the aforementioned herbicides fb 2,4-DB at 0.22 kg ai/ha plus chlorimuron at 0.14 kg ai/ha applied late POST. No cover crop was effective in controlling weeds without a herbicide program. However, when black oat or rye was utilized with PRE fb POST herbicides, weed control was similar to the high input system in two out of three years. Yield increased in 14 of 27 comparisons following conservation-tilled peanut using the Brazilian cover crop management system, compared to a winter fallow system. Yields never decreased following a winter cover crop compared to winter fallow. The winter fallow, high herbicide input system yielded between 7 and 26% less peanut compared to the highest yielding system that included a winter cover crop. The Brazilian system using black oat or rye cover crop has potential to increase peanut productivity and reduce herbicide inputs for peanuts grown in the Southeast.
  • Authors:
    • Lightle, D. T.
    • Karlen, D. L.
    • Johnson, J. M. F.
    • Wilhelm, W. W.
  • Source: Agronomy Journal
  • Volume: 99
  • Issue: 6
  • Year: 2007
  • Summary: Sustainable aboveground crop biomass harvest estimates for cellulosic ethanol production, to date, have been limited by the need for residue to control erosion. Recently, estimates of the amount of corn (Zea mays L.) stover needed to maintain soil carbon, which is responsible for favorable soil properties, were reported (5.25-12.50 Mg ha-1). These estimates indicate stover needed to maintain soil organic carbon, and thus productivity, are a greater constraint to environmentally sustainable cellulosic feedstock harvest than that needed to control water and wind erosion. An extensive effort is needed to develop advanced cropping systems that greatly expand biomass production to sustainably supply cellulosic feedstock without undermining crop and soil productivity.
  • Authors:
    • Arkebauer, T. J.
    • Grant, R. F.
    • Dobermann, A.
    • Hubbard, K. G.
    • Schimelfenig, T. T.
    • Verma, S. B.
    • Suyker, A. E.
    • Walters, D. T.
  • Source: Agronomy Journal
  • Volume: 99
  • Issue: 6
  • Year: 2007
  • Summary: Estimates of agricultural C sequestration require an understanding of how net ecosystem productivity (NEP) and net biome productivity (NBP) are affected by land use. Such estimates will most likely be made using mathematical models that have undergone well-constrained tests against field measurements of CO 2 exchange as affected by management. We tested a hydraulically driven soil-plant-atmosphere C and water transfer scheme in ecosys against CO 2 and energy exchange measured by eddy covariance (EC) over irrigated and rainfed no-till maize-soybean rotations at Mead, NE. Correlations between modeled and measured fluxes ( R2>0.8) indicated that <20% of variation in EC fluxes could not be explained by the model. Annual aggregations of modeled fluxes indicated that NEP of irrigated and rainfed soybean in 2002 was -30 and -9 g C m -2 yr -1 (net C source) while NEP of irrigated and rainfed maize in 2003 was 615 and 397 g C m -2 yr -1 (net C sink). These NEPs were within the range of uncertainty in annual NEP estimated from gap-filled EC fluxes. When grain harvests were subtracted from NEP to calculate NBP, both the modeled and measured maize-soybean rotations became net C sources of 40 to 80 g C m -2 yr -1 during 2002 and 2003. Long-term model runs (100 yr) under repeated 2001-2004 weather sequences indicated that a rainfed no-till maize-soybean rotation at Mead would lose about 30 g C m -2 yr -1. Irrigating this rotation would raise SOC by an average of 6 g C m -2 yr -1 over rainfed values. Modeled and measured results indicated only limited opportunity for long-term soil C storage in irrigated or rainfed maize-soybean rotations under the soil, climate, and management typical of intensive crop production in the U.S. Midwest.
  • Authors:
    • Paustian, K.
    • Williams, S.
    • Easter, M.
    • Breidt, F. J.
    • Ogle, S. M.
  • Source: Ecological Modelling
  • Volume: 205
  • Issue: 3-4
  • Year: 2007
  • Summary: Simulation modelling is used to estimate C sequestration associated with agricultural management for purposes of greenhouse gas mitigation. Models are not completely accurate or precise estimators of C pools, however, due to insufficient knowledge and imperfect conceptualizations about ecosystem processes, leading to uncertainty in the results. It can be difficult to quantify the uncertainty using traditional error propagation techniques, such as Monte Carlo Analyses, because of the structural complexity of simulation models. Empirically based methods provide an alternative to the error propagation techniques, and our objective was to apply this alternative approach. Specifically, we developed a linear mixed-effect model to quantify both bias and variance in modeled soil C stocks that were estimated using the Century ecosystem simulation model. The statistical analysis was based on measurements from 47 agricultural experiments. A significant relationship was found between model results and measurements although there were biases and imprecision in the modeled estimates. Century under-estimated soil C stocks for several management practices, including organic amendments, no-till adoption, and inclusion of hay or pasture in rotation with annual crops. Century also over-estimated the impact of N fertilization on soil C stocks. For lands set-aside from agricultural production, Century under-estimated soil C stocks on low carbon soils and over-estimated the stocks on high carbon soils. Using an empirically based approach allows for simulation model results to be adjusted for biases as well as quantify the variance associated with modeled estimates, according to the measured "reality" of management impacts from a network of experimental sites.
  • Authors:
    • Gal, A.
    • Hegymegi, P.
    • Smith, D. R.
    • Vyn, T. J.
    • Omonode, R.A.
  • Source: Soil & Tillage Research
  • Volume: 95
  • Issue: 1-2
  • Year: 2007
  • Summary: Although the Midwestern United States is one of the world's major agricultural production areas, few studies have assessed the effects of the region's predominant tillage and rotation practices on greenhouse gas emissions from the soil surface. Our objectives were to (a) assess short-term chisel (CP) and moldboard plow (MP) effects on soil CO2 and CH4 fluxes relative to no-till (NT) and, (b) determine how tillage and rotation interactions affect seasonal gas emissions in continuous corn and corn-soybean rotations on a poorly drained Chalmers silty clay loam (Typic Endoaquoll) in Indiana.
  • Authors:
    • VanGessel, M. J.
    • Scott, B. A.
  • Source: Weed Technology
  • Volume: 21
  • Issue: 1
  • Year: 2007
  • Summary: In November 2004, a 29-question survey was mailed to Delaware soybean growers to determine grower perceptions of glyphosate-resistant (GR) horseweed and if glyphosate applications, GR soybean usage, and management practices had been altered in lieu of the presence of resistance. A total of 213 valid responses were received. Ninety-eight percent of respondents reported planting GR soybean at some point in the last 5 yr, with 90% reporting having planted GR soybean 3 or more years. The presence of GR horseweed on-farm was reported by 38% of the respondents and 95% of those growers with GR horseweed on-farm reported implementing one or more changes in GR soybean management. The most frequent change (66% of growers) due to resistant horseweed was the application of another herbicide with a different mode of action before planting. Forty-eight percent of growers with resistance on-farm reported a $5 to $17/ha increase to manage for GR horseweed, with 28% reporting a greater than $17/ha increase. Regardless of experience with GR horseweed, approximately 80% responded that it was worthwhile to incur additional costs now to preserve glyphosate for future use. Soybean grower reliance on glyphosate has not decreased in light of GR horseweed in Delaware. Misconceptions of timing for the selection of GR horseweed biotypes and the future availability of new herbicides with different modes of action exist within the farming community.
  • Authors:
    • Adee, E. A.
    • Nafziger ,E. D.
    • Hoeft, R. G.
    • Lal, R.
    • Jagadamma, S.
  • Source: Soil & Tillage Research
  • Volume: 95
  • Issue: 1-2
  • Year: 2007
  • Summary: Agricultural soils can be a major sink for atmospheric carbon (C) with adoption of recommended management practices (RMPs). Our objectives were to evaluate the effects of nitrogen (N) fertilization and cropping systems on soil organic carbon (SOC) and total N (TN) concentrations and pools. Replicated soil samples were collected in May 2004 to 90 cm depth from a 23-year-old experiment at the Northwestern Illinois Agricultural Research and Demonstration Center, Monmouth, IL. The SOC and TN concentrations and pools, soil bulk density (rho(b)) and soil C:N ratio were measured for five N rates [0 (N-0), 70 (N-1), 140 (N-2), 210 (N-3) and 280 (N-4) kg N ha(-1)] and two cropping systems [continuous corn (Zea mays L.) (CC), and corn-soybean (Glycine max (L.) Merr.) rotation (CS)]. Long-term N fertilization and cropping systems significantly influenced SOC concentrations and pools to 30 cm depth. The SOC pool in 0-30 cm depth ranged from 68.4 Mg ha(-1) for N-0 to 75.8 Mg ha(-1) for N-4. Across all N treatments, the SOC pool in 0-30 cm depth for CC was 4.7 Mg ha(-1) greater than for CS. Similarly, TN concentrations and pools were also significantly affected by N rates. The TN pool for 0-30 cm depth ranged from 5.36 Mg ha(-1) for N-0 to 6.14 Mg ha(-1) for N-4. In relation to cropping systems, the TN pool for 0-20 cm depth for CC was 0.4 Mg ha(-1) greater than for CS. The increase in SOC and TN pools with higher N rates is attributed to the increased amount of biomass production in CC and CS systems. Increasing N rates significantly decreased rho(b) for 0-30 cm and decreased the soil C:N ratio for 0-10 cm soil depth. However, none of the measured soil properties were significantly correlated with N rates and cropping systems below 30 cm, soil depth. We conclude that in the context of developing productive and environmentally sustainable agricultural systems on a site and soil specific basis, the results from this study is helpful to strengthening the database of management effects on SOC storage in the Mollisols of Midwestem U.S. (c) 2007 Elsevier B.V. All rights reserved.
  • Authors:
    • Boast, C. W.
    • Ellsworth, T. R.
    • Mulvaney, R. L.
    • Khan, S. A.
  • Source: Journal of Environmental Quality
  • Volume: 36
  • Issue: 6
  • Year: 2007
  • Summary: Intensive use of N fertilizers in modern agriculture is motivated by the economic value of high grain yields and is generally perceived to sequester soil organic C by increasing the input of crop residues. This perception is at odds with a century of soil organic C data reported herein for Morrow Plots, the world's oldest experimental site under continuous corn (Zea mays L.). After 40 to 50 yr of synthetic fertilization that exceeded grain N removal by 60 to 190%, a net decline occurred in soil C despite increasingly massive residue C incorporation, the decline being more extensive for a corn-soybean (Glycine max L. Merr.) or corn-oats (Avena sativa L.)-hay rotation than for continuous corn and of greater intensity for the profile (0-46 cm) than the surface soil. These findings implicate fertilizer N in promoting the decomposition of crop residues and soil organic matter and are consistent with data from numerous cropping experiments involving synthetic N fertilization in the USA Corn Belt and elsewhere, although not with the interpretation usually provided. These are important implications for soil C sequestration because the yield-based input of fertilizer N has commonly exceeded grain N removal for corn production on fertile soils since the 1960s. To mitigate the ongoing consequences of soil deterioration, atmospheric CO2 enrichment, and NO3- pollution of ground and surface waters, N fertilization should be managed by site-specific assessment of soil N availability. Current fertilizer N managment practices, if combined with corn stover removal for bioenergy production; exacerbate soil C loss.
  • Authors:
    • Field,C. B.
    • Lobell, D. B.
  • Source: Environmental Research Letters
  • Volume: 2
  • Issue: 1
  • Year: 2007
  • Summary: Changes in the global production of major crops are important drivers of food prices, food security and land use decisions. Average global yields for these commodities are determined by the performance of crops in millions of fields distributed across a range of management, soil and climate regimes. Despite the complexity of global food supply, here we show that simple measures of growing season temperatures and precipitation - spatial averages based on the locations of each crop - explain similar to 30% or more of year-to-year variations in global average yields for the world's six most widely grown crops. For wheat, maize and barley, there is a clearly negative response of global yields to increased temperatures. Based on these sensitivities and observed climate trends, we estimate that warming since 1981 has resulted in annual combined losses of these three crops representing roughly 40 Mt or $5 billion per year, as of 2002. While these impacts are small relative to the technological yield gains over the same period, the results demonstrate already occurring negative impacts of climate trends on crop yields at the global scale.
  • Authors:
    • McFee, W. W.
    • Kladivko, E. J.
    • Michéli, E.
    • Vyn, T. J.
    • Gál, A.
  • Source: Soil & Tillage Research
  • Volume: 96
  • Issue: 1-2
  • Year: 2007
  • Summary: Numerous investigators of tillage system impacts on soil organic carbon (OC) or total nitrogen (N) have limited their soil sampling to depths either at or just below the deepest tillage treatment in their experiments. This has resulted in an over-emphasis on OC and N changes in the near-surface zones and limited knowledge of crop and tillage system impacts below the maximum depth of soil disturbance by tillage implements. The objective of this study was to assess impacts of long-term (28 years) tillage and crop rotation on OC and N content and depth distribution together with bulk density and pH on a dark-colored Chalmers silty clay loam in Indiana. Soil samples were taken to 1 m depth in six depth increments from moldboard plow and no-till treatments in continuous corn and soybean-corn rotation. Rotation systems had little impact on the measured soil properties; OC content under continuous corn was not superior to the soybean-corn rotation in either no-till or moldboard plow systems. The increase in OC (on a mass per unit area basis) with no-till relative to moldboard plow averaged 23 t ha(-1) to a constant 30 cm sampling depth, but only 10 t ha(-1) to a constant 1.0 m sampling depth. Similarly, the increase in N with no-till was 1.9 t ha(-1) to a constant 30 cm sampling depth, but only 1.4 t ha(-1) to a constant 1.0 m sampling depth. Tillage treatments also had significant effects on soil bulk density and pH. Distribution of OC and N with soil depth differed dramatically under the different tillage systems. While no-till clearly resulted in more OC and N accumulation in the surface 15 cm than moldboard plow, the relative no-till advantage declined sharply with depth. Indeed, moldboard plowing resulted in substantially more OC and N, relative to no-till, in the 30-50 cm depth interval despite moldboard plowing consistently to less than a 25 cm depth. Our results suggest that conclusions about OC or N gains under long-term no-till are highly dependent on sampling depth and, therefore, tillage comparisons should be based on samples taken well beyond the deepest tillage depth. (c) 2007 Elsevier B.V. All rights reserved.