• Authors:
    • Pan, G.
    • Parton, W. J.
    • Ogle, S. M.
    • Cheng, K.
  • Source: Global Change Biology
  • Volume: 20
  • Issue: 3
  • Year: 2014
  • Summary: Understanding the potential for greenhouse gas (GHG) mitigation in agricultural lands is a critical challenge for climate change policy. This study uses the DAYCENT ecosystem model to predict GHG mitigation potentials associated with soil management in Chinese cropland systems. Application of ecosystem models, such as DAYCENT, requires the evaluation of model performance with data sets from experiments relevant to the climate and management of the study region. DAYCENT was evaluated with data from 350 cropland experiments in China, including measurements of nitrous oxide emissions (N2O), methane emissions (CH4), and soil organic carbon (SOC) stock changes. In general, the model was reasonably accurate with R2 values for model predictions vs. measurements ranging from 0.71 to 0.85. Modeling efficiency varied from 0.65 for SOC stock changes to 0.83 for crop yields. Mitigation potentials were estimated on a yield basis (Mg CO2-equivalent Mg−1Yield). The results demonstrate that the largest decrease in GHG emissions in rainfed systems are associated with combined effect of reducing mineral N fertilization, organic matter amendments and reduced-till coupled with straw return, estimated at 0.31 to 0.83 Mg CO2-equivalent Mg−1Yield. A mitigation potential of 0.08 to 0.36 Mg CO2-equivalent Mg−1Yield is possible by reducing N chemical fertilizer rates, along with intermittent flooding in paddy rice cropping systems.
  • Authors:
    • Zhang, F. S.
    • Chen, X. P.
    • Ma, W. Q.
    • Ye, Y. L.
    • Wu, L.
    • Cui, Z. L.
  • Source: Biogeosciences
  • Volume: 11
  • Issue: 8
  • Year: 2014
  • Summary: Although the concept of producing higher yields with reduced greenhouse gas (GHG) emissions is a goal that attracts increasing public and scientific attention, the tradeoff between high yields and GHG emissions in intensive agricultural production is not well understood. Here, we hypothesize that there exists a mechanistic relationship between wheat grain yield and GHG emission, and that could be transformed into better agronomic management. A total 33 sites of on-farm experiments were investigated to evaluate the relationship between grain yield and GHG emissions using two systems (conventional practice, CP; high-yielding systems, HY) of intensive winter wheat (Triticum aestivum L.) in China. Furthermore, we discussed the potential to produce higher yields with lower GHG emissions based on a survey of 2938 farmers. Compared to the CP system, grain yield was 39% (2352 kg ha(-1)) higher in the HY system, while GHG emissions increased by only 10%, and GHG emission intensity was reduced by 21%. The current intensive winter wheat system with farmers' practice had a median yield and maximum GHG emission rate of 6050 kg ha(-1) and 4783 kg CO2 eq ha(-1), respectively; however, this system can be transformed to maintain yields while reducing GHG emissions by 26% (6077 kg ha(-1), and 3555 kg CO2 eq ha(-1)). Further, the HY system was found to increase grain yield by 39% with a simultaneous reduction in GHG emissions by 18% (8429 kg ha(-1), and 3905 kg CO2 eq ha(-1), respectively). In the future, we suggest moving the trade-off relationships and calculations from grain yield and GHG emissions to new measures of productivity and environmental protection using innovative management technologies.
  • Authors:
    • Wienhold, B.
    • Schmer, M.
    • Venterea, R.
    • Varvel, G.
    • Stott, D.
    • Sauer, T.
    • Osborne, S.
    • Lehman, R.
    • Karlen, D.
    • Johnson, J.
    • Baker, J.
    • Jin, V.
  • Source: Bioenergy Research
  • Volume: 7
  • Issue: 2
  • Year: 2014
  • Summary: In-field measurements of direct soil greenhouse gas (GHG) emissions provide critical data for quantifying the net energy efficiency and economic feasibility of crop residue-based bioenergy production systems. A major challenge to such assessments has been the paucity of field studies addressing the effects of crop residue removal and associated best practices for soil management (i.e., conservation tillage) on soil emissions of carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4). This regional survey summarizes soil GHG emissions from nine maize production systems evaluating different levels of corn stover removal under conventional or conservation tillage management across the US Corn Belt. Cumulative growing season soil emissions of CO2, N2O, and/or CH4 were measured for 2-5 years (2008-2012) at these various sites using a standardized static vented chamber technique as part of the USDA-ARS's Resilient Economic Agricultural Practices (REAP) regional partnership. Cumulative soil GHG emissions during the growing season varied widely across sites, by management, and by year. Overall, corn stover removal decreased soil total CO2 and N2O emissions by -4 and -7 %, respectively, relative to no removal. No management treatments affected soil CH4 fluxes. When aggregated to total GHG emissions (Mg CO2 eq ha(-1)) across all sites and years, corn stover removal decreased growing season soil emissions by -5 +/- 1 % (mean +/- se) and ranged from -36 % to 54 % (n = 50). Lower GHG emissions in stover removal treatments were attributed to decreased C and N inputs into soils, as well as possible microclimatic differences associated with changes in soil cover. High levels of spatial and temporal variabilities in direct GHG emissions highlighted the importance of site-specific management and environmental conditions on the dynamics of GHG emissions from agricultural soils.
  • Authors:
    • Laird, D.
    • Brown, R.
    • Hayes, D.
    • Dumortier, J.
    • Kauffman, N.
  • Source: Biomass & Bioenergy
  • Volume: 63
  • Year: 2014
  • Summary: A partial solution to problems associated with anthropogenic greenhouse gas (GHG) emissions could be the development and deployment of carbon-negative technologies, i.e., producing energy while reducing atmospheric carbon dioxide levels. Biofuels have been considered a possibility but have faced limitations due to competition with food production and GHG emissions through indirect land-use change (ILUC). In this article, we show how emissions from ILUC can potentially be reduced by producing food and bioenergy from biochar amended soils. The possibility of yield improvements from biochar would reduce the land requirement for crop production and thus, lead to a reduction in emissions from ILUC. In our application, biochar and bio-oil are produced via fast pyrolysis of corn stover. ho-oil is subsequently upgraded into a fuel suitable for use in internal combustion engines. Applying the U.S. regulatory method used to determine biofuel life cycle emissions, our results show that a biochar-induced yield improvement in the U.S. Midwest ranging from 1% to 8% above trend can lead to an ILUC credit between 1.65 and 14.79 t CO2- equivalent ha(-1) year(-1) when future emissions are assessed over the next 30 years. The model is generalizable to other feedstocks and locations and illustrates the relationship between biochar and crop production. (C) 2014 Elsevier Ltd. All rights reserved.
  • Authors:
    • Keck, P.
    • Dale, B.
    • Kim, S.
  • Source: Bioenergy Research
  • Volume: 7
  • Issue: 2
  • Year: 2014
  • Summary: This meta-study quantitatively and qualitatively compares 21 published life cycle assessment (LCA)-type studies for energy consumption and greenhouse gas (GHG) emissions of maize production in the USA. Differences between the methodologies and numerical results obtained are described. Nonrenewable energy consumption in maize production (from cradle-to-farm gate) ranges from 1.44 to 3.50 MJ/kg of maize, and GHG emissions associated with maize production range from -27 to 436 g CO2 equivalent/kg of maize. Large variations between studies exist within the input data for lime application, fuels purchased, and life cycle inventory data for fertilizer and agrochemical production. Although most studies use similar methodological approaches, major differences between studies include the following: (1) impacts associated with human labor and farm machinery production, (2) changes in carbon dioxide emissions resulting from soil organic carbon levels, and (3) indirect N2O emissions.
  • Authors:
    • BaoHai, W.
    • Ying, L.
  • Source: Journal of Agricultural Science and Technology (Beijing)
  • Volume: 16
  • Issue: 2
  • Year: 2014
  • Summary: Since entering into the 21st century, greenhouse gas emissions have led to the continued global warming. Low-carbon environment protection has been raised on the agenda. The development of low-carbon eco-agriculture has become an effective way to solve China's agricultural resources exhaustion, to curb environment deterioration, and to achieve the sustainable development of China's agriculture. In 2009, the Yellow River Delta Efficient Ecological Economic Zone rose to the national strategy. Low-carbon agriculture has become the theme for the development of modern agriculture in the Yellow River Delta. This paper analyzed the necessity for the Yellow River Delta to develop Low-Carbon Eco-agriculture. Combining with the status quo of natural resources and environment in this area, and the requirement for developing Low-Carbon agriculture, the paper put up 5 models suitable for the Yellow River Delta to develop Low-Carbon Eco-agriculture. At the same time, a series of suggestions were put forward based on these models.
  • Authors:
    • Tang, X.
    • Hu, C.
    • Zhang, W.
    • Liu, X.
  • Source: Biogeosciences
  • Volume: 11
  • Issue: 6
  • Year: 2014
  • Summary: The objectives of this study were to investigate seasonal variation of greenhouse gas fluxes from soils on sites dominated by plantation (Robinia pseudoacacia, Punica granatum, and Ziziphus jujube) and natural regenerated forests (Vitex negundo var. heterophylla, Leptodermis oblonga, and Bothriochloa ischcemum), and to identify how tree species, litter exclusion, and soil properties (soil temperature, soil moisture, soil organic carbon, total N, soil bulk density, and soil pH) explained the temporal and spatial variation in soil greenhouse gas fluxes. Fluxes of greenhouse gases were measured using static chamber and gas chromatography techniques. Six static chambers were randomly installed in each tree species. Three chambers were randomly designated to measure the impacts of surface litter exclusion, and the remaining three were used as a control. Field measurements were conducted biweekly from May 2010 to April 2012. Soil CO2 emissions from all tree species were significantly affected by soil temperature, soil moisture, and their interaction. Driven by the seasonality of temperature and precipitation, soil CO2 emissions demonstrated a clear seasonal pattern, with fluxes significantly higher during the rainy season than during the dry season. Soil CH4 and N2O fluxes were not significantly correlated with soil temperature, soil moisture, or their interaction, and no significant seasonal differences were detected. Soil organic carbon and total N were significantly positively correlated with CO2 and N2O fluxes. Soil bulk density was significantly negatively correlated with CO2 and N2O fluxes. Soil pH was not correlated with CO2 and N2O emissions. Soil CH4 fluxes did not dis-play pronounced dependency on soil organic carbon, total N, soil bulk density, and soil pH. Removal of surface litter significantly decreased in CO2 emissions and CH4 uptakes. Soils in six tree species acted as sinks for atmospheric CH4. With the exception of Ziziphus jujube, soils in all tree species acted as sinks for atmospheric N2O. Tree species had a significant effect on CO2 and N2O releases but not on CH4 uptake. The lower net global warming potential in natural regenerated vegetation suggested that natural regenerated vegetation were more desirable plant species in reducing global warming.
  • Authors:
    • Braden, J. B.
    • Cai, X.
    • Eheart, J. W.
    • Ng, T. L.
    • Czapar, G. F.
  • Source: Journal of Water Resources Planning and Management
  • Volume: 140
  • Issue: 1
  • Year: 2014
  • Summary: Excessive nitrate loads in surface waters are a major cause of hypoxia and eutrophication. In many places, agriculture is the single largest source of nitrogen entering receiving waters. Perennial energy grass crops have the potential to reduce nitrogen loads from agricultural areas, while sequestering carbon and offering new economic opportunities for farmers. This study analyzes farm system-scale cropping and fertilizer application decisions, and resulting nitrate loads, as driven by prices for the bioenergy crop miscanthus, as well as investigates reductions of carbon and other greenhouse gas emissions and nitrogen fertilizer use. An economic model of farm-system-scale decisions is coupled to a hydrologic-agronomic model of the physical stream system to obtain nitrate loading and crop yield results for varying combinations of prices and policies for a typical Midwestern agricultural watershed. For the scenarios examined, a large reduction in stream nitrate load depends on a high price for miscanthus relative to competing crops. A price for miscanthus that exceeds 50% of the average of corn and soybean prices, per unit weight, is estimated to lead to nitrate load reductions of 25% or more. Though significant, these reductions are still less than the recommended 45% reduction in stream nitrogen flux entering the Gulf of Mexico needed to mitigate the hypoxia problem in the gulf. Miscanthus prices are unlikely ever to reach such levels. However, nitrate load reductions could still be achieved by implementing a nitrogen fertilizer reduction subsidy alongside a miscanthus market. The results also show that carbon trading is unlikely to result in any significant reduction in nitrate load. The results are useful for improving understanding of the potential of these incentives, individually and concurrently, to reduce pollution from Midwestern crop agriculture.
  • Authors:
    • Horwath, W. R.
    • Zhu, X.
    • You, M.
    • Han, X.
    • Miao, S.
    • Qiao, Y.
  • Source: Field Crops Research
  • Volume: 161
  • Year: 2014
  • Summary: Long-term agronomic studies are useful to determine cropping system nitrogen (N) use efficiency and the fate of applied fertilizers. We used a subtractive fertilizer experiment incorporating N, phosphorous (P), potassium (K) and swine manure to determine long-term changes in grain yield, soil organic carbon (SOC), total soil nitrogen (N), as well as carbon dioxide (CO2) and nitrous oxide (N2O) emissions. The experiment was conducted on a 22-year maize-soybean-wheat rotation in Northeastern China. Crop residues were removed for cooking fuel and forage according to local practices. Five fertilizer treatments were applied annually: control (no fertilizer), NK, NP, NPK, and NPKOM (N, P. K and manure). The NPKOM treatment increased SOC and total soil N by 4.59 and 0.45 Mg ha(-1), respectively. In contrast, SOC decreased by 10.6 and 6.64 Mg ha(-1) in the control and NK treatments, respectively. The NPKOM treatment had an average of 2.9 times more N2O emissions than the other fertilizer treatments. The cropping system balances for N and SOC, together with fuel use for farming practices and manure handling, were used to calculate the global warming potential (GWP) of the different fertilizer treatments. Due to SOC sequestration, the GWP of the NPKOM treatment (6.77 Mg C equivalent ha(-1)) was significantly lower than that of both the control (14.4 Mg C equivalent ha(-1)) and the NK treatment (12.8 Mg C equivalent ha(-1)). The results suggest that in rainfed agricultural systems in Northeastern China, the application of manure supplemented with NPK can simultaneously achieve higher grain yield and lower GWP compared to mineral fertilizers alone.
  • Authors:
    • Chen, Q.
    • Wang, J. G.
    • Ren, T.
  • Source: International Society for Horticultural Science, Acta Horticulturae
  • Issue: 1018
  • Year: 2014
  • Summary: Organic manure is one of the most important factors to maintain soil fertility and achieve high yield in greenhouse vegetable production. Effects of organic manure, mineral nitrogen application and wheat straw incorporation on C cycling was investigated based on a six-year greenhouse tomato experiment in Shandong Province, northern China. In contrast to the amount of 0.14 t C ha -1 a -1 contributed by root residue, chicken manure, with 3.80 t C ha -1 a -1, was the dominant C supplement. Without any manure application, soil organic carbon and soil non-labile carbon fraction significantly decreased after 6 years of intensive tomato production. High chicken manure applied rates ranging from 13 to 20 t ha -1 a -1 only could maintain SOC content at their initial levels in the greenhouse. Based on the organic manure application, little effect of different mineral N application rate on SOC content was observed. Manure and straw incorporation significantly enhanced soil respiration rate, especially for straw incorporation, which led to higher negative net ecosystem productivity. Meanwhile no significant increase of SOC content was observed with manure and straw incorporation. High organic carbon decomposition rate due to year-round high temperature and moisture and excessive manure with low C/N ratio might be the dominant reason for the low accumulated rate of soil organic matter in this greenhouse tomato planting system. How to improve the soil organic matter further will be a great challenge in greenhouse vegetable production.