• Authors:
    • McDaniel, M. D.
    • Wickings, K.
    • Salam, D. S.
    • Grandy, A. S.
    • Culman, S. W.
    • Snapp, S. S.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 179
  • Year: 2013
  • Summary: Litter decomposition dynamics are influenced by soil nutrient status, yet the specific effects of soil nitrogen (N) on litter decomposition in agricultural systems are not well understood. We explored litter decomposition and related soil organic matter dynamics in no-till, corn-based Midwestern U.S. cropping systems receiving 0, 134, and 291 kg N ha -1 y -1. We found that total soil carbon (C) and N, light fraction organic matter, and permanganate oxidizable C were similar among treatments, but N fertilization at rates of 134 and 291 kg N ha -1 y -1 reduced potentially mineralizable C by as much as 37% and 58%, respectively, compared to the unfertilized treatment. Litter mass remaining after one year of field decomposition was greater with wheat litter (37%) than with corn litter (23%), but was not influenced by N fertilizer rate. In litter, N fertilization led to increases in the activities of two hydrolase enzymes involved in simple carbohydrate metabolism (beta-d-cellobiohydrolase and beta-1,4-glucosidase) and periodic increases in one related to N metabolism (beta-1,4-N-acetylglucosaminidase), but had no effects on enzymes regulating the breakdown of aromatic compounds (phenol oxidase), or on enzymes measured in the soil. N fertilization also decreased arthropod densities in decomposing litter. We found contrasting effects of N fertilizer on processes regulating decomposition, but altogether our results were consistent with a limited or nil role for N fertilization in accelerating litter and soil C turnover, and thus do not support N fertilization as a contributor to depletion of C stocks in agricultural soils.
  • Authors:
    • Reyes-Fox, M.
    • Ascough, J.
    • Liebig, M. A.
    • Gollany, H. T.
    • Archer, D. W.
    • Franzluebbers, A. J.
    • Johnson, J. M. F.
    • Follett, R. F.
    • Karlen, D. L.
    • Vandenberg, B.
    • Wilson, G.
    • White, J. W.
    • Grosso, S. J. del
    • Pellack, L.
    • Starr, J.
    • Barbour, N.
    • Polumsky, R. W.
    • Gutwein, M.
    • James, D.
  • Source: Journal of Environmental Quality
  • Volume: 42
  • Issue: 4
  • Year: 2013
  • Summary: Difficulties in accessing high-quality data on trace gas fluxes and performance of bioenergy/bioproduct feedstocks limit the ability of researchers and others to address environmental impacts of agriculture and the potential to produce feedstocks. To address those needs, the GRACEnet (Greenhouse gas Reduction through Agricultural Carbon Enhancement network) and REAP (Renewable Energy Assessment Project) research programs were initiated by the USDA Agricultural Research Service (ARS). A major product of these programs is the creation of a database with greenhouse gas fluxes, soil carbon stocks, biomass yield, nutrient, and energy characteristics, and input data for modeling cropped and grazed systems. The data include site descriptors (e.g., weather, soil class, spatial attributes), experimental design (e.g., factors manipulated, measurements performed, plot layouts), management information (e.g., planting and harvesting schedules, fertilizer types and amounts, biomass harvested, grazing intensity), and measurements (e.g., soil C and N stocks, plant biomass amount and chemical composition). To promote standardization of data and ensure that experiments were fully described, sampling protocols and a spreadsheet-based data-entry template were developed. Data were first uploaded to a temporary database for checking and then were uploaded to the central database. A Web-accessible application allows for registered users to query and download data including measurement protocols. Separate portals have been provided for each project (GRACEnet and REAP) at nrrc.ars.usda.gov/slgracenet/#/Home and nrrc.ars.usda.gov/slreap/#/Home. The database architecture and data entry template have proven flexible and robust for describing a wide range of field experiments and thus appear suitable for other natural resource research projects.
  • Authors:
    • Norton, J. B.
    • Hurisso, T. T.
    • Norton, U.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 181
  • Year: 2013
  • Summary: Conversion of native prairie land for agricultural production has resulted in significant loss and redistribution of soil organic matter (SOM) in the soil profile ultimately leading to declining soil fertility in a low-productivity semiarid agroecosystem. Improved understanding of such losses can lead to development of sustainable land management practices that maintain soil fertility and enhance soil quality. This study was conducted to determine whether conservation practices impact soil profile carbon (C) and nitrogen (N) accumulation in central High Plains. Soil samples were taken at four-depth increments to 1.2 m in July of 2011 from five unfertilized fields under long-term management with varying degrees of soil disturbance: (1) historic wheat ( Triticum aestivum)-fallow (HT) - managed with tillage alone, (2) conventional wheat-fallow (CT) - input of herbicides for weed control and fewer tillage operation than historic wheat-fallow, (3) no-till wheat-fallow (NT) - not plowed since 2000 and herbicides used for weed control, (4) grass-legume mixture - established in 2005 as in the Conservation Reserve Program (CRP), and (5) native mixed grass prairie (NP) - representing a relatively undisturbed reference location. Cumulative soil organic C (SOC) was not significantly different among the three wheat-fallow systems when the whole profile (0-120 cm) was analyzed. However, SOC, dissolved organic C (DOC), and total soil N contents decreased in the direction NP > CRP ≥ NT > HT ≥ CT in the surface 0-30 cm depth. In the surface 0-30 cm depth, estimated annual SOC storage rate averaged 0.28 Mg C ha -1 year -1 since the cessation of tillage in 2000 and 0.58 Mg C ha -1 year -1 since the establishment of CRP grass-legume mixture in 2005. Cumulative soil inorganic C (SIC) accumulation ranged between 8.1 and 24.9 Mg ha -1and was greatest under wheat-fallow systems, particularly at deeper soil layers, relative to the perennial systems (NP and CRP). Results from this study suggest that repeated soil disturbance induced by cropping and fallow favored large accumulation of SIC which presence may result in decline in soil fertility and productivity; whereas conversion from tilled wheat-fallow to CRP grass-legume mixture offers great SOC storage potential relative to NT wheat-fallow practices.
  • Authors:
    • Markelz, R. J. C.
    • Ruiz-Vera, U. M.
    • Siebers, M. H.
    • Vanloocke, A.
    • Hussain, M. Z.
    • Leakey, A. D. B.
    • Ort, D. R.
    • Bernacchi, C. J.
  • Source: Global Change Biology
  • Volume: 19
  • Issue: 5
  • Year: 2013
  • Summary: Maize, in rotation with soybean, forms the largest continuous ecosystem in temperate North America, therefore changes to the biosphere-atmosphere exchange of water vapor and energy of these crops are likely to have an impact on the Midwestern US climate and hydrological cycle. As a C 4 crop, maize photosynthesis is already CO 2-saturated at current CO 2 concentrations ([CO 2]) and the primary response of maize to elevated [CO 2] is decreased stomatal conductance ( gs). If maize photosynthesis is not stimulated in elevated [CO 2], then reduced gs is not offset by greater canopy leaf area, which could potentially result in a greater ET reduction relative to that previously reported in soybean, a C 3 species. The objective of this study is to quantify the impact of elevated [CO 2] on canopy energy and water fluxes of maize ( Zea mays). Maize was grown under ambient and elevated [CO 2] (550 mol mol -1 during 2004 and 2006 and 585 mol mol -1 during 2010) using Free Air Concentration Enrichment (FACE) technology at the SoyFACE facility in Urbana, Illinois. Maize ET was determined using a residual energy balance approach based on measurements of sensible ( H) and soil heat fluxes, and net radiation. Relative to control, elevated [CO 2] decreased maize ET (7-11%; P<0.01) along with lesser soil moisture depletion, while H increased (25-30 W m -2; P<0.01) along with higher canopy temperature (0.5-0.6°C). This reduction in maize ET in elevated [CO 2] is approximately half that previously reported for soybean. A partitioning analysis showed that transpiration contributed less to total ET for maize compared to soybean, indicating a smaller role of stomata in dictating the ET response to elevated [CO 2]. Nonetheless, both maize and soybean had significantly decreased ET and increased H, highlighting the critical role of elevated [CO 2] in altering future hydrology and climate of the region that is extensively cropped with these species.
  • Authors:
    • Adviento-Borbe, M. A.
    • Six, J.
    • Venterea, R.
    • Kessel, C. van
    • Linquist, B.
    • Groenigen, K. J. van
  • Source: Global Change Biology
  • Volume: 19
  • Issue: 1
  • Year: 2013
  • Summary: No-tillage and reduced tillage (NT/RT) management practices are being promoted in agroecosystems to reduce erosion, sequester additional soil C and reduce production costs. The impact of NT/RT on N 2O emissions, however, has been variable with both increases and decreases in emissions reported. Herein, we quantitatively synthesize studies on the short- and long-term impact of NT/RT on N 2O emissions in humid and dry climatic zones with emissions expressed on both an area- and crop yield-scaled basis. A meta-analysis was conducted on 239 direct comparisons between conventional tillage (CT) and NT/RT. In contrast to earlier studies, averaged across all comparisons, NT/RT did not alter N 2O emissions compared with CT. However, NT/RT significantly reduced N 2O emissions in experiments >10 years, especially in dry climates. No significant correlation was found between soil texture and the effect of NT/RT on N 2O emissions. When fertilizer-N was placed at ≥5 cm depth, NT/RT significantly reduced area-scaled N 2O emissions, in particular under humid climatic conditions. Compared to CT under dry climatic conditions, yield-scaled N 2O increased significantly (57%) when NT/RT was implemented <10 years, but decreased significantly (27%) after ≥10 years of NT/RT. There was a significant decrease in yield-scaled N 2O emissions in humid climates when fertilizer-N was placed at ≥5 cm depth. Therefore, in humid climates, deep placement of fertilizer-N is recommended when implementing NT/RT. In addition, NT/RT practices need to be sustained for a prolonged time, particularly in dry climates, to become an effective mitigation strategy for reducing N 2O emissions.
  • Authors:
    • Taliaferro, C. M.
    • Kakani, V. G.
    • Zhang, H.
    • Wu, Y. Q.
    • Makaju, S. O.
    • Anderson, M. P.
  • Source: Agronomy Journal
  • Volume: 105
  • Issue: 2
  • Year: 2013
  • Summary: The maximum biomass yield of switchgrass ( Panicum virgatum L.) usually is achieved with one seasonal autumn harvest. However, information is limited on the influences of winter harvesting on annual biomass yield and on quality parameters impacting conversion into bioethanol. Accordingly, the objectives of this study were to assess: (i) yield of standing field cured biomass at monthly intervals through winter, (ii) year-round elemental composition of biomass, and (iii) associated year-round soil nutrient status. An unfertilized 'Kanlow' switchgrass planting established in 1998 was used for this study conducted from November 2007 to October 2010. The experimental treatment was monthly harvest from November to the following March and year-round monthly sampling of biomass (except April) and soil for chemical analyses. The 3-yr mean dry matter yield of winter harvests was 5.94Mg ha -1, ranging from 3.88 Mg ha -1 in the winter of 2007-2008 to 7.55 Mg ha -1 in 2009-2010. Monthly biomass yield differences were significant in Years 1 and 3 but not in Year 2. Concentrations of biomass elements and soil nutrients changed with various degrees over the 3 yr. Concentrations of ash, cell wall components, and mineral nutrients, except P, K, and S, did not change appreciably across winter months. Early winter harvests resulted in less yield loss compared to late winter harvests. These findings will be valuable in harvest management for switchgrass biomass production.
  • Authors:
    • Schulte, L. A.
    • Brown, P. W.
    • McGranahan, D. A.
    • Tyndall, J. C.
  • Source: Journal of Soil and Water Conservation
  • Volume: 68
  • Issue: 3
  • Year: 2013
  • Authors:
    • Arbuckle, J. G.
    • Hobbs, J.
    • Morton, L. W.
  • Source: Journal of Soil and Water Conservation
  • Volume: 68
  • Issue: 1
  • Year: 2013
  • Summary: Nitrogen (N) is critical for maintaining crop yields; however, current agricultural management practices are major contributors to high levels of N and other agricultural chemicals leaking into neighboring water bodies thereby limiting the achievement of sustainability goals for water resources. Changes in farmer beliefs over time about sustainability goals and production inputs reveal increasing uncertainty about the connection between sustainability and their practices. Inference from a multinomial model analysis of farmer beliefs from 1989 to 2002 shows increasing odds of being uncertain about whether use of sustainable farming practices help maintain the natural resource base. Almost 29% of the population of a 2002 random sample survey of Iowa farmers was uncertain about sustainable farming practices compared to 18.8% in 1989. Further, farmers were increasingly uncertain over time as to whether modern farming relies too heavily upon commercial fertilizers, insecticides, and herbicides. In 2002, 14.5% of farmers, compared to 8.4% in 1994 and 5.7% in 1989, were uncertain about whether heavy reliance on commercial fertilizers was a sustainability problem. Multinomial logistic regression models examining responses to various farming practices reveal that the ratio of disagree/agree increases over time and is influenced by total corn and soybean acres farmed, net of farmer age, and weather conditions. Models of uncertainty controlling for age and weather conditions show increasing farmer uncertainty about sustainable farming practices; natural resource base maintenance; and whether modern farming relies too heavily on commercial fertilizers, insecticides, and herbicides.
  • Authors:
    • Gurgel, A. C.
    • Nardy, V.
  • Source: Nova Economia
  • Volume: 23
  • Issue: 3
  • Year: 2013
  • Summary: This paper investigates the potential impacts from a cut in the U.S. trade tariffs to the Brazilian ethanol on land use and greenhouse gas emissions from such changes. A version of the GTAP global economic model is used to simulate how an increase in the Brazilian ethanol production could affect land use and CO 2 emissions in the country and worldwide. The results indicate an increases in cropland areas and decrease in pastureland and forest areas, with small increments in CO 2 emissions, which are offset by lower emissions from reduced consumption of fossil fuels. It can be concluded that the potential of sugarcane ethanol in reducing net greenhouse gas emissions is not affected by the trade liberalization, even when changes in land use are considered.
  • Authors:
    • Miller, P. R.
    • O'Dea, J. K.
    • Jones, C. A.
  • Source: JOURNAL OF SOIL AND WATER CONSERVATION
  • Volume: 68
  • Issue: 4
  • Year: 2013
  • Summary: Replacing summer fallow practices with annual legumes as green manures (LGMs) may increase the sustainability of northern Great Plains wheat (Triticum aestivum L.) systems. Viability hinges on soil water use management and realizing biologically fixed nitrogen (N) benefits. Plot-scale research has shown that managing LGMs with first-flower stage termination and no-till practices conserves soil water and that rotational N benefits can increase wheat grain quality Nonetheless, farmer adoption of LGMs has been negligible. To better understand this practice and its regional adoption potential, we conducted a participatory on-farm assessment of no-till LGM versus summer fallow wheat rotations in north-central Montana. Soil water and nitrate (NO3) levels to 0.9 m (3 ft), potentially mineralizable N (PMN) to 0.3 m (1 ft), wheat yields, conservation potential, and producer adoption challenges were assessed at five farmer-managed, field-scale sites. Compared to fallow, LGM treatment diminished mean wheat yield by 6% (0.24 Mg ha(-1) [3.7 bu ac(-1)]), diminished grain protein by 9 g kg(-1) when wheat was fertilized with N (p = 0.01), and increased grain protein by 5 g kg(-1) when wheat was unfertilized (p = 0.08). Small soil water depletions in LGM treatments below fallow at wheat seeding (17%; 30 mm [1.2 in]) and near-record high rainfall during the wheat growing season (280 to 380 mm [11 to 14 in]) suggest that LGMs likely did not limit soil water available to wheat in this study. Soil NO3 levels following LGMs were 29% to 56% less than summer fallow at wheat seeding, and conversely, greater PMN was detected in LGM treatments at 3 of 5 sites. We theorize that N mineralization from LGMs was insubstantial by wheat seeding due to dry soil conditions and low LGM biomass N contributions, consequently affecting wheat yield potential due to limited early season soil N availability. LGMs increased average use efficiency of available N by 24% during the wheat year and increased total residue carbon (C) and N returned to soils by 260 and 26 kg ha(-1) (232 and 23 lb ac(-1)), respectively, after two years. Our results illustrated that farmers viably managed LGM soil water use with early termination and no-till practices but that LGM adoption may be hindered by a lack of immediate wheat yield or protein benefits from legume-N and seed costs for LGMs. Appropriate incentives, management strategies, and yield benefit expectations (short versus long term) should be fostered to increase the adoption potential of this N-economizing soil and water conservation strategy.