• Authors:
    • Möller,K.
  • Source: Agronomy for Sustainable Development
  • Volume: 35
  • Issue: 3
  • Year: 2015
  • Summary: Sustainability in agriculture means the inclusion of several aspects, as sustainable agriculture systems must not compromise not only their ability to satisfy future needs by undermining soil fertility and the natural resource base but also sustainable agriculture has had to address a range of other issues including energy use, efficient use, and recycling of nutrients, the effects on adjacent ecosystems including the effects on water bodies and climate change. Organic manures are an important factor to keep the soil fertility level of soils. However, their management is often related to large emissions. In this context, anaerobic digestion is—similarly to composting—a treatment option for stabilization of biogenic wastes leading to a residual product called digestates, enabling the sanitation and the recycling and use as fertilizer. It is also a means to obtain energy from wastes as well as from dedicated energy crops. Therefore, anaerobic digestion potentially addresses several aspects of agricultural sustainability. This review discusses the current state of knowledge on the effects of anaerobic digestion on organic compounds in digestates and the most important processes influencing N emissions in the field, as well as the possible long-term effects on soil microbial biomass and soil fertility. The main findings are that (1) the direct effects of anaerobic digestion on long-term sustainability in terms of soil fertility and environmental impact at the field level are of minor relevance. (2) The most relevant effects of anaerobic digestion on soil fertility as well as on N emissions will be expected from indirect effects related to cropping system changes such as changes in crop rotation, crop acreage, cover cropping, and total amounts of organic manures including digestates. Furthermore, (3) the remaining organic fraction after anaerobic digestion is much more recalcitrant than the input feedstocks leading to a stabilization of the organic matter and a lower organic matter degradation rate after field application, enabling a similar reproduction of the soil organic matter as obtained by direct application of the feedstock or by composting of the feedstock. (4) Regarding emissions, the main direct effect of anaerobic digestion on a farm level is the influence on gaseous emissions during manure or digestate treatment and handling, whereas the direct effects of anaerobic digestion on a field level on emissions (NH3− and N2O− emissions, NO3- leaching) are negligible or at least ambiguous. (5) The main direct effects of anaerobic digestion on the field level are short-term effects on soil microbial activity and changes in the soil microbial community. Therefore, in terms of the effects on agricultural sustainability, potential cropping system-based changes induced by introduction of biogas plants are probably much more relevant for the overall performance and sustainability of the cropping system than the direct effects triggered by application of digestates in comparison to the undigested feedstocks. Furthermore, to get the full potential advances from implementation of biogas plants in terms of improvement of the nutrient use efficiency and reduction of greenhouse gas emissions, there is the need to introduce more sophisticated techniques to avoid counteracting effects by pollution swapping, e.g., by gas-tight closure of the digestate stores and direct soil incorporation of the field-applied digestates. © 2015, INRA and Springer-Verlag France.
  • Authors:
    • Monier,Erwan
    • Gao,Xiang
  • Source: Climatic Change
  • Volume: 131
  • Issue: 1
  • Year: 2015
  • Summary: In this study, we analyze changes in extreme temperature and precipitation over the US in a 60-member ensemble simulation of the 21st century with the Massachusetts Institute of Technology (MIT) Integrated Global System Model-Community Atmosphere Model (IGSM-CAM). Four values of climate sensitivity, three emissions scenarios and five initial conditions are considered. The results show a general intensification and an increase in the frequency of extreme hot temperatures and extreme precipitation events over most of the US. Extreme cold temperatures are projected to decrease in intensity and frequency, especially over the northern parts of the US. This study displays a wide range of future changes in extreme events in the US, even simulated by a single climate model. Results clearly show that the choice of policy is the largest source of uncertainty in the magnitude of the changes. The impact of the climate sensitivity is largest for the unconstrained emissions scenario and the implementation of a stabilization scenario drastically reduces the changes in extremes, even for the highest climate sensitivity considered. Finally, simulations with different initial conditions show conspicuously different patterns and magnitudes of changes in extreme events, underlining the role of natural variability in projections of changes in extreme events.
  • Authors:
    • Russell,J. R.
    • Bisinger,J. J.
  • Source: Journal of Animal Science
  • Volume: 93
  • Issue: 6
  • Year: 2015
  • Summary: Beyond grazing, managed grasslands provide ecological services that may offer economic incentives for multifunctional use. Increasing biodiversity of plant communities may maximize net primary production by optimizing utilization of available light, water, and nutrient resources; enhance production stability in response to climatic stress; reduce invasion of exotic species; increase soil OM; reduce nutrient leaching or loading in surface runoff; and provide wildlife habitat. Strategically managed grazing may increase biodiversity of cool-season pastures by creating disturbance in plant communities through herbivory, treading, nutrient cycling, and plant seed dispersal. Soil OM will increase carbon and nutrient sequestration and water-holding capacity of soils and is greater in grazed pastures than nongrazed grasslands or land used for row crop or hay production. However, results of studies evaluating the effects of different grazing management systems on soil OM are limited and inconsistent. Although roots and organic residues of pasture forages create soil macropores that reduce soil compaction, grazing has increased soil bulk density or penetration resistance regardless of stocking rates or systems. But the effects of the duration of grazing and rest periods on soil compaction need further evaluation. Because vegetative cover dissipates the energy of falling raindrops and plant stems and tillers reduce the rate of surface water flow, managing grazing to maintain adequate vegetative cover will minimize the effects of treading on water infiltration in both upland and riparian locations. Through increased diversity of the plant community with alterations of habitat structure, grazing systems can be developed that enhance habitat for wildlife and insect pollinators. Although grazing management may enhance the ecological services provided by grasslands, environmental responses are controlled by variations in climate, soil, landscape position, and plant community resulting in considerable spatial and temporal variation in the responses. Furthermore, a single grazing management system may not maximize livestock productivity and each of the potential ecological services provided by grasslands. Therefore, production and ecological goals must be integrated to identify the optimal grazing management system.
  • Authors:
    • Wise,M.
    • Hodson,E. L.
    • Mignone,B. K.
    • Clarke,L.
    • Waldhoff,S.
    • Luckow,P.
  • Source: Energy Economics
  • Volume: 50
  • Year: 2015
  • Summary: Accurately characterizing the emissions implications of bioenergy is increasingly important to the design of regional and global greenhouse gas mitigation policies. Market-based policies, in particular, often use information about carbon intensity to adjust relative deployment incentives for different energy sources. However, the carbon intensity of bioenergy is difficult to quantify because carbon emissions can occur when land use changes to expand production of bioenergy crops rather than simply when the fuel is consumed as for fossil fuels. Using a long-term, integrated assessment model, this paper develops an approach for computing the carbon intensity of bioenergy production that isolates the marginal impact of increasing production of a specific bioenergy crop in a specific region, taking into account economic competition among land uses. We explore several factors that affect emissions intensity and explain these results in the context of previous studies that use different approaches. Among the factors explored, our results suggest that the carbon intensity of bioenergy production from land use change (LUC) differs by a factor of two depending on the region in which the bioenergy crop is grown in the United States. Assumptions about international land use policies (such as those related to forest protection) and crop yields also significantly impact carbon intensity. Finally, we develop and demonstrate a generalized method for considering the varying time profile of LUC emissions from bioenergy production, taking into account the time path of future carbon prices, the discount rate and the time horizon. When evaluated in the context of power sector applications, we found electricity from bioenergy crops to be less carbon-intensive than conventional coal-fired electricity generation and often less carbon-intensive than natural-gas fired generation. © 2015 Elsevier B.V.
  • Authors:
    • Brookes,G.
    • Barfoot,P.
  • Source: GM Crops & Food
  • Volume: 7
  • Issue: 2
  • Year: 2015
  • Summary: This paper updates previous assessments of how crop biotechnology has changed the environmental impact of global agriculture. It focuses on the environmental impacts associated with changes in pesticide use and greenhouse gas emissions arising from the use of GM crops since their first widespread commercial use in the mid 1990s. The adoption of GM insect resistant and herbicide tolerant technology has reduced pesticide spraying by 553 million kg (-8.6%) and, as a result, decreased the environmental impact associated with herbicide and insecticide use on these crops (as measured by the indicator the Environmental Impact Quotient (EIQ)) by 19.1%. The technology has also facilitated important cuts in fuel use and tillage changes, resulting in a significant reduction in the release of greenhouse gas emissions from the GM cropping area. In 2013, this was equivalent to removing 12.4 million cars from the roads.
  • Authors:
    • Congreves,K. A.
    • Van Eerd,L. L.
  • Source: Nutrient Cycling in Agroecosystems
  • Volume: 102
  • Issue: 3
  • Year: 2015
  • Summary: Vegetables are important horticultural commodities with high farm gate values and nutritional quality. For many vegetables, growers apply large amounts of N fertilizer (> 200 kg N ha(-1)) to increase yield and profits, but such high N fertilizer applications can pose a significant threat for N loss and environmental contamination via denitrification, volatilization, leaching, runoff, and erosion. Nitrogen losses can reduce air and water quality by contributing to greenhouse gas emissions, ground-level ozone and particulate matter production, ground and surface water contamination, and eutrophication. The processes governing N loss include a complex of biological, physical, and chemical factors, which are impacted by management practices, climatic conditions and soil properties. Therefore, we reviewed and evaluated various management practices for minimizing N loss in N-intensive vegetable production within a temperate climate. Most soil nutrient management practices have focused on reducing N loss throughout the growing season, but the risk for N loss is very high after harvesting vegetables with low N harvest indices, low C:N ratios, and high quantities of N in crop residues, such as most Brassica oleracea L. crops. Amending soil with organic C material may present a novel strategy for reducing N losses after harvest by 37 %, compared to the typical practice of incorporating N-rich vegetable crop residues. Research must focus on testing new and innovative methods of minimizing post-harvest N loss in intensive horticulture.
  • Authors:
    • Dare,Anne
  • Source: Journal of Soil and Water Conservation
  • Volume: 70
  • Issue: 4
  • Year: 2015
  • Authors:
    • Hao,B.
    • Xue,Q.
    • Marek,T. H.
    • Jessup,K. E.
    • Becker,J.
    • Hou,X.
    • Xu,W.
    • Bynum,E. D.
    • Bean,B. W.
    • Colaizzi,P. D.
    • Howell,T. A.
  • Source: Agronomy Journal
  • Volume: 107
  • Issue: 5
  • Year: 2015
  • Summary: Drought is an important factor limiting corn ( Zea mays L.) yields in the Texas High Plains, and adoption of drought-tolerant (DT) hybrids could be a management tool under water shortage. We conducted a 3-yr field study to investigate yield, evapotranspiration (ET), and water use efficiency (WUE) in DT hybrids. One conventional (33D49) and 4 DT hybrids (P1151HR, P1324HR, P1498HR, and P1564HR) were grown at three water regimes (I 100, I 75, and I 50, referring to 100, 75, and 50% ET requirement) and three planting densities (PD) (5.9, 7.4, and 8.4 plants m -2). Yield (13.56 Mg ha -1) and ET (719 mm) were the greatest at I 100 but WUE (2.1 kg m -3) was the greatest at I 75. Although DT hybrids did not always have greater yield and WUE than 33D49 at I 100, hybrids P1151HR and P1564HR consistently had greater yield and WUE than 33D49 at I 75 and I 50. Compared to 33D49, P1151HR and P1564HR had 8.6 to 12.1% and 19.1% greater yield at I 75 and I 50, respectively. Correspondingly, WUE was 9.8 to 11.7% and 20.0% greater at I 75 and I 50, respectively. Greater PD resulted in greater yield and WUE at I 100 and I 75 but PD did not affect yield and WUE at I 50. Yield and WUE in greater PD (8.4 plants m -2) were 6.3 to 8.3% greater than those in smaller PD (5.9 plants m -2). The results of this study demonstrated that proper selection of DT hybrids can increase corn yield and WUE under water-limited conditions.
  • Authors:
    • Jacinthe,P. A.
    • Vidon,P.
    • Fisher,K.
    • Liu,X.
    • Baker,M. E.
  • Source: Journal of Environmental Quality
  • Volume: 44
  • Issue: 4
  • Year: 2015
  • Summary: Riparian buffers contribute to the mitigation of nutrient pollution in agricultural landscapes, but there is concern regarding their potential to be hot spots of greenhouse gas production. This study compared soil CO 2 and CH 4 fluxes in adjacent crop fields and riparian buffers (a flood-prone forest and a flood-protected grassland along an incised channel) and examined the impact of water table depth (WTD) and flood events on the variability of gas fluxes in riparian zones. Results showed significantly ( P22°C), but the effect of flooding was less pronounced in early spring (emission <1.06 mg CH 4-C m -2 d -1), probably due to low soil temperature. Although CH 4 flux direction alternated at all sites, overall the croplands and the flood-affected riparian forest were CH 4 sources, with annual emission averaging +0.040.17 and +0.921.6 kg CH 4-C ha -1, respectively. In the riparian forest, a topographic depression (<8% of the total area) accounted for 78% of the annual CH 4 emission, underscoring the significance of landscape heterogeneity on CH 4 dynamics in riparian buffers. The nonflooded riparian grassland, however, was a net CH 4 sink (-1.080.22 kg CH 4-C ha -1 yr -1), probably due to the presence of subsurface tile drains and a dredged/incised channel at that study site. Although these hydrological alterations may have contributed to improvement in the CH 4 sink strength of the riparian grassland, this must be weighed against the water quality maintenance functions and other ecological services provided by riparian buffers.
  • Authors:
    • Li,Na
    • Ning,Tangyuan
    • Cui,Zhengyong
    • Tian,Shenzhong
    • Li,Zengjia
    • Lal,Rattan
  • Source: Nutrient Cycling in Agroecosystems
  • Volume: 102
  • Issue: 3
  • Year: 2015
  • Summary: Fertilizer application and tillage practices play an important role in agricultural production, whereas excess N input could create considerable N2O emissions. However, it is unclear whether urea types under subsoiling or rotary tillage have effects on yield and N2O emissions in maize field. We investigated the effects on N2O emissions and maize (Zea mays L.) yield of tillage (rotary tillage [R] alone and rotary tillage following subsoiling [S]) and two types of urea (polymer-coated urea [P] and conventional urea [C]) applications, respectively, at the sowing [0] and V6 [6] stages in a clay loam soil. N2O emissions varied from 1 to 11 kg N2O-N ha(-1). Compared with S soil, the R soils produced greater N2O emissions. Compared with conventional urea, polymer-coated urea increased maize production and fertilizer-induced N2O emission, but had no significant effect on yield scaled N2O emission. The increase of N2O emission was mainly related to water-filled pore space affected by tillage and soil nitrate and ammonium N concentrations affected by urea types. Polymer-coated urea topdressing at the V6 stage in S soils was better for producing a higher yield with lower N2O emission. The results indicate that R soils had more significant N2O emission than S soils during a wet climate; and polymer-coated urea can increase grain yield with a slight higher N2O emissions, whereas changing the application stage can decrease the cumulative N2O emissions without reducing the yield.