• Authors:
    • Thompson, J.
    • Curan, D.
    • Hammer, G. L.
    • Sinclair, T. R.
    • Messina, C. D.
    • Oler, Z.
    • Gho, C.
    • Cooper, M.
  • Source: Agronomy Joural
  • Volume: 107
  • Issue: 6
  • Year: 2015
  • Summary: Yield loss due to water deficit is ubiquitous in maize ( Zea mays L.) production environments in the United States. The impact of water deficits on yield depends on the cropping system management and physiological characteristics of the hybrid. Genotypic diversity among maize hybrids in the transpiration response to vapor pressure deficit (VPD) indicates that a limited-transpiration trait may contribute to improved drought tolerance and yield in maize. By limiting transpiration at VPD above a VPD threshold, this trait can increase both daily transpiration efficiency and water availability for late-season use. Reduced water use, however, may compromise yield potential. The complexity associated with genotype * environment * management interactions can be explored in a quantitative assessment using a simulation model. A simulation study was conducted to assess the likely effect of genotypic variation in limited-transpiration rate on yield performance of maize at a regional scale in the United States. We demonstrated that the limited-transpiration trait can result in improved maize performance in drought-prone environments and that the impact of the trait on maize productivity varies with geography, environment type, expression of the trait, and plant density. The largest average yield increase was simulated for drought-prone environments (135 g m -2), while a small yield penalty was simulated for environments where water was not limiting (-33 g m -2). Outcomes from this simulation study help interpret the ubiquitous nature of variation for the limited-transpiration trait in maize germplasm and provide insights into the plausible role of the trait in past and future maize genetic improvement.
  • Authors:
    • Cai, X.
    • Zhuang, Q.
    • Qin, Z.
  • Source: Original Research
  • Volume: 7
  • Issue: 6
  • Year: 2015
  • Summary: Growing biomass feedstocks from marginal lands is becoming an increasingly attractive choice for producing biofuel as an alternative energy to fossil fuels. Here, we used a biogeochemical model at ecosystem scale to estimate crop productivity and greenhouse gas (GHG) emissions from bioenergy crops grown on marginal lands in the United States. Two broadly tested cellulosic crops, switchgrass, and Miscanthus, were assumed to be grown on the abandoned land and mixed crop-vegetation land with marginal productivity. Production of biomass and biofuel as well as net carbon exchange and nitrous oxide emissions were estimated in a spatially explicit manner. We found that, cellulosic crops, especially Miscanthus could produce a considerable amount of biomass, and the effective ethanol yield is high on these marginal lands. For every hectare of marginal land, switchgrass and Miscanthus could produce 1.0-2.3kl and 2.9-6.9kl ethanol, respectively, depending on nitrogen fertilization rate and biofuel conversion efficiency. Nationally, both crop systems act as net GHG sources. Switchgrass has high global warming intensity (100-390g CO(2)eql(-1) ethanol), in terms of GHG emissions per unit ethanol produced. Miscanthus, however, emits only 21-36g CO(2)eq to produce every liter of ethanol. To reach the mandated cellulosic ethanol target in the United States, growing Miscanthus on the marginal lands could potentially save land and reduce GHG emissions in comparison to growing switchgrass. However, the ecosystem modeling is still limited by data availability and model deficiencies, further efforts should be made to classify crop-specific marginal land availability, improve model structure, and better integrate ecosystem modeling into life cycle assessment.
  • Authors:
    • DeSutter, T.
    • Clay, S. A.
    • Mishra, U.
    • Dunn, B. H.
    • Reitsma, K. D.
    • Clay, D. E.
  • Source: Agronomy Journal
  • Volume: 107
  • Issue: 6
  • Year: 2015
  • Summary: A growing world population and climate change are expected to influence future agricultural productivity and land use. This study determined the impact of land-use change on soil sustainability and discussed the factors contributing to these changes. South Dakota was selected as a model system because corn ( Zea mays L.) grain prices tripled between 2006 and 2012 and it is located in a climate and grassland/cropland transition zone. High resolution imagery was used to visually determine land uses (cropland, grassland, nonagricultural, habitat, and water) at 14,400 points in 2006 and 2012. At each point, land-use change and the USDA land capability class (LCC) were determined. Over the 6-yr study period, 6.87% of the grasslands (730,000 ha) were converted to cropland, with 93% occurring on lands generally considered suitable for crop production (LCC ≤ IV) if appropriate practices are followed. Converted grasslands, however, had higher LCC values than existing croplands and lower LCC values than remaining grasslands. In addition, 4.2% of the croplands (250,000 ha) were converted to grasslands, and statewide, 20,000 ha of croplands were converted to grasslands in areas limited by excess water (LCC V). The conversion of grasslands could not be linked to one specific factor and may be related to: (i) a desire to increase financial returns, (ii) changes in the land ownership structure, (iii) technology improvements, (iv) governmental policies, (v) climate change, and (vi) an aging workforce. Research and outreach programs that balance the goods and services of different land uses are needed to maintain sustainable agroecosystems.
  • Authors:
    • Drag, D. W.
    • Siebers, M. H.
    • Ruiz-Vera, U. M.
    • Ort, D. R.
    • Bernacchi, C. J.
  • Source: Primary Research Article
  • Volume: 21
  • Issue: 11
  • Year: 2015
  • Summary: Rising atmospheric CO 2 concentration ([CO 2]) and attendant increases in growing season temperature are expected to be the most important global change factors impacting production agriculture. Although maize is the most highly produced crop worldwide, few studies have evaluated the interactive effects of elevated [CO 2] and temperature on its photosynthetic physiology, agronomic traits or biomass, and seed yield under open field conditions. This study investigates the effects of rising [CO 2] and warmer temperature, independently and in combination, on maize grown in the field throughout a full growing season. Free-air CO 2 enrichment (FACE) technology was used to target atmospheric [CO 2] to 200 mol mol -1 above ambient [CO 2] and infrared heaters to target a plant canopy increase of 3.5°C, with actual season mean heating of ~2.7°C, mimicking conditions predicted by the second half of this century. Photosynthetic gas-exchange parameters, leaf nitrogen and carbon content, leaf water potential components, and developmental measurements were collected throughout the season, and biomass and yield were measured at the end of the growing season. As predicted for a C 4 plant, elevated [CO 2] did not stimulate photosynthesis, biomass, or yield. Canopy warming caused a large shift in aboveground allocation by stimulating season-long vegetative biomass and decreasing reproductive biomass accumulation at both CO 2 concentrations, resulting in decreased harvest index. Warming caused a reduction in photosynthesis due to down-regulation of photosynthetic biochemical parameters and the decrease in the electron transport rate. The reduction in seed yield with warming was driven by reduced photosynthetic capacity and by a shift in aboveground carbon allocation away from reproduction. This field study portends that future warming will reduce yield in maize, and this will not be mitigated by higher atmospheric [CO 2] unless appropriate adaptation traits can be introduced into future cultivars.
  • Authors:
    • Gleason, R.
    • Finocchiaro, R.
    • Tangen, B.
  • Source: Science of the Total Environment
  • Volume: 533
  • Year: 2015
  • Summary: Wetland restoration has been suggested as policy goal with multiple environmental benefits including enhancement of atmospheric carbon sequestration. However, there are concerns that increased methane (CH4) emissions associated with restoration may outweigh potential benefits. A comprehensive, 4-year study of 119 wetland catchments was conducted in the Prairie Pothole Region of the north-central U.S. to assess the effects of land use on greenhouse gas (GHG) fluxes and soil properties. Results showed that the effects of land use on GHG fluxes and abiotic soil properties differed with respect to catchment zone (upland, wetland), wetland classification, geographic location, and year. Mean CH4 fluxes from the uplands were predictably low (<0.02 g CH4 m(-2) day(-1)), while wetland zone CH4 fluxes were much greater (<0.001-3.9 g CH4 m(-2) day(-1)). Mean cumulative seasonal CH4 fluxes ranged from roughly 0-650 g CH4 m(-2), with an overall mean of approximately 160 g CH4 m(-2). These maximum cumulative CH4 fluxes were nearly 3 times as high as previously reported in North America. The overall magnitude and variability of N2O fluxes from this study (<0.0001-0.0023 g N2O m(-2) day(-1)) were comparable to previously reported values. Results suggest that soil organic carbon is lost when relatively undisturbed catchments are converted for agriculture, and that when non-drained cropland catchments are restored, CH4 fluxes generally are not different than the pre-restoration baseline. Conversely, when drained cropland catchments are restored, CH4 fluxes are noticeably higher. Consequently, it is important to consider the type of wetland restoration (drained, non-drained) when assessing restoration benefits. Results also suggest that elevated N2O fluxes from cropland catchments likely would be reduced through restoration. The overall variability demonstrated by this study was consistent with findings of other wetland investigations and underscores the difficulty in quantifying the GHG balance of wetland systems. Published by Elsevier B.V.
  • Authors:
    • Vogel, A.
    • Strecker, T.
    • Steinauer, K.
    • Richter, A.
    • Ramirez, N.
    • Pierce, S.
    • Rong, J.
    • HongYan, G.
    • FuXun, A.
    • Tilman, D.
    • Scheu, S.
    • Reich, P.
    • Power, S.
    • Roscher, C.
    • Niklaus, P.
    • Manning, P.
    • Milcu, A.
    • Thakur, M.
    • Eisenhauer, N.
  • Source: Global Change Biology
  • Volume: 21
  • Issue: 11
  • Year: 2015
  • Summary: Soil microbial biomass is a key determinant of carbon dynamics in the soil. Several studies have shown that soil microbial biomass significantly increases with plant species diversity, but it remains unclear whether plant species diversity can also stabilize soil microbial biomass in a changing environment. This question is particularly relevant as many global environmental change (GEC) factors, such as drought and nutrient enrichment, have been shown to reduce soil microbial biomass. Experiments with orthogonal manipulations of plant diversity and GEC factors can provide insights whether plant diversity can attenuate such detrimental effects on soil microbial biomass. Here, we present the analysis of 12 different studies with 14 unique orthogonal plant diversity * GEC manipulations in grasslands, where plant diversity and at least one GEC factor (elevated CO 2, nutrient enrichment, drought, earthworm presence, or warming) were manipulated. Our results show that higher plant diversity significantly enhances soil microbial biomass with the strongest effects in long-term field experiments. In contrast, GEC factors had inconsistent effects with only drought having a significant negative effect. Importantly, we report consistent non-significant effects for all 14 interactions between plant diversity and GEC factors, which indicates a limited potential of plant diversity to attenuate the effects of GEC factors on soil microbial biomass. We highlight that plant diversity is a major determinant of soil microbial biomass in experimental grasslands that can influence soil carbon dynamics irrespective of GEC.
  • Authors:
    • Myers, G.
    • Dodla, S.
    • Zhang, Z.
    • Liu, S.
    • Wang, J.
    • Tian, Z.
  • Source: Science of the Total Environment
  • Volume: 533
  • Year: 2015
  • Summary: Nitrogen (N) fertilization affects both ammonia (NH3) and greenhouse gas (GHG) emissions that have implications in air quality and global warming potential. Different cropping systems practice varying N fertilizations. The aim of this study was to investigate the effects of applications of polymer-coated urea and urea treated with N process inhibitors: NBPT [N-(n-butyl) thiophosphoric triamide], urease inhibitor, and DCD [Dicyandiamide], nitrification inhibitor, on NH3 and GHG emissions from a cotton production systemin the Mississippi delta region. A two-year field experiment consisting of five treatments including the Check (unfertilized), urea, polymer-coated urea (ESN), urea + NBPT, and urea + DCD was conducted over 2013 and 2014 in a Cancienne loam (Fine-silty, mixed, superactive, nonacid, hyperthermic Fluvaquentic Epiaquepts). Ammonia and GHG samples were collected using active and passive chamber methods, respectively, and characterized. The results showed that the N loss to the atmosphere following urea-N application was dominated by a significantly higher emission of N2O-N than NH3-N and the most N2O-N and NH3-N emissions were during the first 30-50 days. Among different N treatments compared to regular urea, NBPT was the most effective in reducing NH3-N volatilization (by 58-63%), whereas DCD the most significant in mitigating N2O-N emissions (by 75%). Polymer-coated urea (ESN) and NBPT also significantly reduced N2O-N losses (both by 52%) over urea. The emission factors (EFs) for urea, ESN, urea-NBPT, urea + DCD were 1.9%, 1.0%, 0.2%, 0.8% for NH3-N, and 8.3%, 3.4%, 3.9%, 1.0% for N2O-N, respectively. There were no significant effects of different N treatments on CO2-C and CH4-C fluxes. Overall both of these N stabilizers and polymer-coated urea could be used as a mitigation strategy for reducing N2O emission while urease inhibitor NBPT for reducing NH3 emission in the subtropical cotton production system of the Mississippi delta region. (C) 2015 Elsevier B.V. All rights reserved.
  • Authors:
    • Lehmann, J.
    • Vanek, S.
  • Source: Plant and Soil
  • Volume: 395
  • Issue: 1/2
  • Year: 2015
  • Summary: Background and aims: We sought to understand biochar's role in promoting plant phosphorus (P) access via arbuscular mycorrhizas (AM), focusing on whether P solubility and biochar-P proximity altered AM enhancement of P uptake in a mycorrhizal crop legume. Methods: A greenhouse study compared feedstock-derived P with 50 mg P pot -1 of sparingly soluble FePO 4 (Fe-P) or soluble NaH 2PO 4 (Na-P) at different proximities to biochar (co-pyrolyzed, mixed with biochar, mixed with soil) on Phaseolus vulgaris P uptake, specific root length (SRL), AM colonization, AM neutral lipids, and microbial biomass-P. Results: Biochar increased AM colonization by 6% ( p2*) with AM hyphae. Biochar-P proximity did not alter P uptake, but shifted uptake towards AM for Fe-P and roots for Na-P. Soluble P located on biochar increased total plant+microbial P ( p<0.05). Biochar reversed ( p<0.05) reductions in SRL induced by AM. Conclusions: Biochar enhanced AM's access to sparingly soluble P, and root/microbial access to soluble P. Biochar augments sparingly soluble P uptake at scales larger than biochar particles, perhaps by reducing P sorption or facilitating root/hyphal exploration.
  • Authors:
    • Wilkens,S.
    • Weimer,P. J.
    • Lauer,J. G.
  • Source: Agronomy Journal
  • Volume: 107
  • Issue: 6
  • Year: 2015
  • Summary: Full-season corn ( Zea mays L.) hybrids take advantage of more of the growing season than shorter-season hybrids often leading to greater grain and biomass yield. Many agronomic experiments aimed at corn stover production have been performed at forage harvest rather than later when stover is normally harvested for biofuel measurements. The objective of this research was to evaluate the influence of hybrid relative maturity (days RM) on stover ethanol production, ruminant digestibility, and biomass composition. Hybrids selected were high-yielding commercial grain hybrids grown throughout Wisconsin and ranged from 85 to 115 d RM in 10 d RM increments during 2009, and in 5 d RM increments during 2010. Hybrids were harvested at physiological maturity or after a killing frost. Overall, stover and theoretical ethanol yields increased as RM increased at a linear rate of 0.211 Mg ha -1 RM -1 and 67.1 L ha -1 RM -1. Stover nutritional and biomass composition improved as RM increased, but yield variability was greater than nutritional and biomass compositional variability. Increasing ethanol yields will likely occur by increasing stover yields rather than by altering stover composition. Therefore, until price premiums for stover composition are made available to farmers for ethanol production, the adoption of full-season or longer maturing hybrids should be implemented for increased stover and ethanol yields.
  • Authors:
    • Johnson, J.
    • Ortiz, B. V.
    • Woli, P.
    • Hoogenboom, G.
  • Source: Agronomy Journal
  • Volume: 107
  • Issue: 6
  • Year: 2015
  • Summary: The winter wheat ( Triticum aestivum L.) growing season in the southeastern United States occurs during the period when the climate of this region is strongly influenced by El Nino-Southern Oscillation (ENSO). The ENSO-based interannual climate variability might influence growth, maturity, and yield of winter wheat. Because different maturity groups of wheat cultivars head at different times of the year, the groups are expected to have different impacts of climate variability. This study examined whether the yield difference between early and late maturity groups of winter wheat cultivars grown in this region were associated with ENSO-based climate. Data on yield, planting date, and heading date were obtained for a number of wheat cultivars grown at four locations in Georgia during the 1975 to 2012 period. Wheat cultivars were classified according to heading date as early or late maturity, and yield differences between maturity groups and among ENSO phases were examined using the Wilcoxon rank sum test. Results showed that the early maturity group could out-yield the late maturity group in southern locations during La Nina, whereas the late group could out-yield the early group in northern locations during El Nino. Of all ENSO phases, La Nina was associated with the largest yields. During El Nino, the yield difference between early and late groups increased with an increase in latitude, whereas during La Nina, the yield difference increased with a decrease in latitude. These findings might be helpful to wheat growers in this region in optimizing decisions regarding planting date and cultivar selection to reduce the risks related to climate variability.