• Authors:
    • Venkat, K.
  • Source: Journal of Sustainable Agriculture
  • Volume: 36
  • Issue: 6
  • Year: 2012
  • Summary: Given the growing importance of organic food production, there is a pressing need to understand the relative environmental impacts of organic and conventional farming methods. This study applies standards-based life cycle assessment to compare the cradle-to-farm gate greenhouse gas emissions of 12 crop products grown in California using both organic and conventional methods. In addition to analyzing steady-state scenarios in which the soil organic carbon stocks are at equilibrium, this study models a hypothetical scenario of converting each conventional farming system to a corresponding organic system and examines the impact of soil carbon sequestration during the transition. The results show that steady-state organic production has higher emissions per kilogram than conventional production in seven out of the 12 cases (10.6% higher overall, excluding one outlier). Transitional organic production performs better, generating lower emissions than conventional production in seven cases (17.7% lower overall) and 22.3% lower emissions than steady-state organic. The results demonstrate that converting additional cropland to organic production may offer significant GHG reduction opportunities over the next few decades by way of increasing the soil organic carbon stocks during the transition. Nonorganic systems could also improve their environmental performance by adopting management practices to increase soil organic carbon stocks.
  • Authors:
    • Ouyang, Z.
    • Wang, X.
    • Wang, S.
  • Source: Journal of Environmental Sciences
  • Volume: 24
  • Issue: 3
  • Year: 2012
  • Summary: Soil organic carbon (SOC) and total nitrogen (TN) contents as well as their relationships with site characteristics are of profound importance in assessing current regional, continental and global soil C and N stocks and potentials for C sequestration and N conservation to offset anthropogenic emissions of greenhouse gases. This study investigated contents and distribution of SOC and TN under different land uses, and the quantitative relationships between SOC or TN and site characteristics in the Upstream Watershed of Miyun Reservoir, North China. Overall, both SOC and TN contents in natural secondary forests and grasslands were much higher than in plantations and croplands. Land use alone explained 37.2% and 38.4% of variations in SOC and TN contents, respectively. The optimal models for SOC and TN, achieved by multiple regression analysis combined with principal component analysis (PCA) to remove the multicollinearity among site variables, showed that elevation, slope, soil clay and water contents were the most significant factors controlling SOC and TN contents, jointly explaining 70.3% of SOC and 67.1% of TN contents variability. Only does additional 1.9% and 3% increase in the interpretations of SOC and TN contents variability respectively when land use was added to regressions, probably due to environment factors determine land use. Therefore, environmental variables were more important for SOC and TN variability than land use in the study area, and should be taken into consideration in properly evaluating effects of future land use changes on SOC and TN on a regional scale.
  • Authors:
    • Six, J.
    • Tian,Jing
    • Kuzyakov, Y.
    • Lee, J.
    • Chen, H.
    • Christie, P.
    • Li, X.
    • Zhang, F.
    • Fan, M.
    • Yan, Y.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 150
  • Year: 2012
  • Summary: The conversion from cereal fields to vegetable production in the last three decades represents a significant shift in land use in China. Here, we studied the effects of conversion form cereal fields to vegetable production in north China on soil organic carbon (SOC) and total nitrogen (TN) in both bulk soil and soil aggregates. We used two approaches: (1) measurements of paired soil samples from wheat (Triticum aestivum L) - maize (Zea mays L) fields and adjacent greenhouses vegetable fields in three vegetable production areas representing various management intensities in terms of C and N inputs and frequency of tillage: (2) fractionating soil to distinguish intra-aggregate particulate organic matter (iPOM) and organo-mineral complexes (silt + clay). Our results indicated that converting cereal fields to greenhouse vegetable production with intermediate and high management intensity led to increases in SOC and TN and decreases in C:N ratios in the top soil. The accumulation rates of C and N in the surface soil (0-30 cm) were estimated to be 1.37 Mg C ha(-1) yr(-1) and 0.21 Mg N ha(-1) yr(-1) over an average period of 8 years after cereal fields to greenhouse vegetable production conversion. At the soil aggregate level, only the coarse (>250 mu m) and fine (53-250 mu m) iPOM fraction contributed to the increases in soil C (e.g., 49% and 51% of total C increases, respectively), while the coarse and fine iPOM, and silt + clay fraction accounted for 22%, 30% and 48%, respectively, of total N increases. This illustrates how the addition of readily available C (manure) and N (manure and inorganic N) leads to a temporary stabilization of C in relatively labile SOM fractions, but to a preferential stabilization of N in organo-mineral SOM fractions. In conclusion, the conversion to highly intensive vegetable systems in China leads to marked differences in C and N stabilization dynamics.
  • Authors:
    • Kang, H.
    • Yoo, G.
  • Source: Journal of Environmental Quality
  • Volume: 41
  • Issue: 4
  • Year: 2012
  • Summary: Biochar application to soil has drawn much attention as a strategy to sequester atmospheric carbon in soil ecosystems. The applicability of this strategy as a climate change mitigation option is limited by our understanding of the mechanisms responsible for the observed changes in greenhouse gas emissions from soils, microbial responses, and soil fertility changes. We conducted an 8-wk laboratory incubation using soils from PASTURE (silt loam) and RICE PADDY (silt loam) sites with and without two types of biochar (biochar from swine manure [CHAR-M] and from barley stover [CHAR-B]). Responses to addition of the different biochars varied with the soil source. Addition of CHAR-B did not change CO2 and CH4 evolution from the PASTURE or the RICE PADDY soils, but there was a decrease in N2O emissions from the PASTURE soil. The effects of CHAR-M addition on greenhouse gas emissions were different for the soils. The most substantial change was an increase in N2O emissions from the RICE PADDY soil. This result was attributed to a combination of abundant denitrifiers in this soil and increased net nitrogen mineralization. Soil phosphatase and N-acetylglucosaminidase activity in the CHAR-B-treated soils was enhanced compared with the controls for both soils. Fungal biomass was higher in the CHAR-B-treated RICE PADDY soil. From our results, we suggest CHAR-B to be an appropriate amendment for the PASTURE and RICE PADDY soils because it provides increased nitrogen availability and microbial activity with no net increase in greenhouse gas emissions. Application of CHAR-M to RICE PADDY soils could result in excess nitrogen availability, which may increase N2O emissions and possible NO 3 leaching problems. Thus, this study confirms that the ability of environmentally sound biochar additions to sequester carbon in soils depends on the characteristics of the receiving soil as well as the nature of the biochar.
  • Authors:
    • Zhang, H.
    • Chen, F.
    • Kong, F.
    • Wei, Y.
    • Zhang, M.
  • Source: Transactions of the Chinese Society of Agricultural Engineering
  • Volume: 28
  • Issue: 6
  • Year: 2012
  • Summary: Distribution of soil organic carbon in different soil layer can be transformed by tillage practices, and then soil carbon storage was changed. The four indices of soil organic carbon (SOC), soil carbon density (SCD), soil respiration (SR) and biomass carbon (BC) were selected to verify the adaptability of DNDC model in North China based on model adaptation and then the model was used to simulate local dynamic change of soil carbon storage (SCS) and characteristics of greenhouse gas emission. The result showed that there was a high similarity between simulated values and observed values and the model proposed was suitable to apply to the simulation research of soil organic carbon for winter wheat-summer corn in North China. SOC and SCS simulated by the model increased from 2001-2010, and simulated data in the next 100 years showed that SOC with rotary tillage (RT), conventional tillage (CT) and no-tillage (NT) showed a severe rising tendency in the first 15 years, and rising tendency of NT could sustain for 40 years. By comparing changes of soil carbon storage for 100 years between each treatment, it was found that SCS values with CT were the highest in the first 20 years and SCS values with NT was the highest after first 20 years. The sequence of global warming potential (GWP) for each treatment was CT > RT > NT. The results showed that DNDC model could work well for winter wheat-summer corn in North China, and NT was beneficial to increase SCS and decrease GWP of farmland in the long run. It provides a reference for fixing carbon and reducing discharge of winter wheat-summer corn in North China.
  • Authors:
    • Zhang, X.
    • Zheng, J.
    • Li, L.
    • Hussain, Q.
    • Pan, G.
    • Liu, Y.
    • Zhang, A.
  • Source: Plant and Soil
  • Volume: 351
  • Issue: 1-2
  • Year: 2012
  • Summary: A field experiment was conducted to investigate the effect of biochar on maize yield and greenhouse gases (GHGs) in a calcareous loamy soil poor in organic carbon from Henan, central great plain, China. Biochar was applied at rates of 0, 20 and 40 t ha(-1) with or without N fertilization. With N fertilization, urea was applied at 300 kg N ha(-1), of which 60% was applied as basal fertilizer and 40% as supplementary fertilizer during crop growth. Soil emissions of CO2, CH4 and N2O were monitored using closed chambers at 7 days intervals throughout the whole maize growing season (WMGS). Biochar amendments significantly increased maize production but decreased GHGs. Maize yield was increased by 15.8% and 7.3% without N fertilization, and by 8.8% and 12.1% with N fertilization under biochar amendment at 20 t ha(-1) and 40 t ha(-1), respectively. Total N2O emission was decreased by 10.7% and by 41.8% under biochar amendment at 20 t ha(-1) and 40 t ha(-1) compared to no biochar amendment with N fertilization. The high rate of biochar (40 t ha(-1)) increased the total CO2 emission by 12% without N fertilization. Overall, biochar amendments of 20 t ha(-1) and 40 t ha(-1) decreased the total global warming potential (GWP) of CH4 and N2O by 9.8% and by 41.5% without N fertilization, and by 23.8% and 47.6% with N fertilization, respectively. Biochar amendments also decreased soil bulk density and increased soil total N contents but had no effect on soil mineral N. These results suggest that application of biochar to calcareous and infertile dry croplands poor in soil organic carbon will enhance crop productivity and reduce GHGs emissions.
  • Authors:
    • Cotrufo, M. F.
    • Stewart, C. E.
    • Zheng, J.
  • Source: Journal of Environmental Quality
  • Volume: 41
  • Issue: 5
  • Year: 2012
  • Summary: Biochar (BC) application to agricultural soils could potentially sequester recalcitrant C, increase N retention, increase water holding capacity, and decrease greenhouse gas (GHG) emissions. Biochar addition to soils can alter soil N cycling and in some cases decrease extractable mineral N (NO3- and NH4+) and N2O emissions. These benefits are not uniformly observed across varying soil types, N fertilization, and BC properties. To determine the effects of BC addition on N retention and GHG flux, we added two sizes (>250 and <250 mu m) of oak-derived BC (10% w/w) to two soils (aridic Argiustoll and aquic Haplustoll) with and without N fertilizer and measured extractable NO3- and NH4+ and GHG efflux (N2O, CO2, and CH4) in a 123-d laboratory incubation. Biochar had no effect on NO3-, NH4+, or N2O in the unfertilized treatments of either soil. Biochar decreased cumulative extractable NO3- in N fertilized treatments by 8% but had mixed effects on NH4+. Greenhouse gas efflux differed substantially between the two soils, but generally with N fertilizer BC addition decreased N2O 3 to 60%, increased CO2 10 to 21%, and increased CH4 emissions 5 to 72%. Soil pH and total treatment N (soil + fertilizer + BC) predicted soil N2O flux well across these two different soils. Expressed as CO2 equivalents, BC significantly reduced GHG emissions only in the N-fertilized silt loam by decreasing N2O flux. In unfertilized soils, CO2 was the dominant GHG component, and the direction of the flux was mediated by positive or negative BC effects on soil CO2 flux. On the basis of our data, the use of BC appears to be an effective management strategy to reduce N leaching and GHG emissions, particularly in neutral to acidic soils with high N content.
  • Authors:
    • Chen, C.
    • Yang, M.
    • Zhu, L.
  • Source: Journal of Agricultural Science
  • Volume: 4
  • Issue: 9
  • Year: 2012
  • Summary: Carbon sequestration in cropland soils which could be achieved through improved management practices (IPMs) represents an important opportunity to offset a portion of greenhouse gas emissions. North China is the main wheat and maize production region where many IMPs have been widely used during the last several decades, but the effect size and duration of IMPs on soil organic carbon (SOC) sequestration in wheat-maize double cropping system in this region is scarcely studied. In this study, a meta-analysis was conducted to compare the effect size and duration of four IMPs on SOC sequestration in wheat-maize double cropping system in north China. A total of 29 long-term experiments, consisting of 119 paired treatments were compiled in this analysis. The results indicated that the four IMPs of organic manure application (OM), organic manure combined with chemical fertilizer application (MF), straw return (SR) and reduced or no tillage (RNT) all had significant effects on SOC sequestration in the study area. On average, the IMPs of OM, MF, SR and RNT enhanced SOC density by 260, 328, 278 and 134 kg ha -1 yr -1, respectively. The effect duration of OM, MF, SR and RNT on SOC sequestration were about 48, 26, 22 and 18 years, respectively. Accumulation enhancements of SOC for OM, MF, SR and RNT over SOC sequestration period were about 34.7%, 36.1%, 22.0% and 12.7%, respectively. OM and MF could be the appropriate practices on SOC sequestration in wheat-maize double cropping system in the research area.
  • Authors:
    • Shaver, G. R.
    • Reich, P. B.
    • Pendall, E.
    • Mitchell, R. J.
    • Melillo, J. M.
    • Hobbie, S. E.
    • Frey, S. D.
    • Dukes, J. S.
    • Blair, J. M.
    • Brzostek, E. R.
    • Stefanski, A.
    • Tjoelker, M. G.
    • Finzi, A. C.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 8
  • Year: 2012
  • Summary: Nitrogen regulates the Earth's climate system by constraining the terrestrial sink for atmospheric CO 2. Proteolytic enzymes are a principal driver of the within-system cycle of soil nitrogen, yet there is little to no understanding of their response to climate change. Here, we use a single methodology to investigate potential proteolytic enzyme activity in soils from 16 global change experiments. We show that regardless of geographical location or experimental manipulation (i.e., temperature, precipitation, or both), all sites plotted along a single line relating the response ratio of potential proteolytic activity to soil moisture deficit, the difference between precipitation and evapotranspiration. In particular, warming and reductions in precipitation stimulated potential proteolytic activity in mesic sites - temperate and boreal forests, arctic tundra - whereas these manipulations suppressed potential activity in dry grasslands. This study provides a foundation for a simple representation of the impacts of climate change on a central component of the nitrogen cycle.
  • Authors:
    • Reitsma, K.
    • Carlson, G. C.
    • Gelderman, R. H.
    • Stone, J.
    • Clay, S. A.
    • Chang, J. Y.
    • Clay, D. E.
    • Jones, M.
    • Janssen, L.
    • Schumacher, T.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 3
  • Year: 2012
  • Summary: The corn (Zea mays L.)-based ethanol carbon footprint is impacted by many factors including the soil's C sequestration potential. The study's objective was to determine the South Dakota corn-based ethanol surface SOC sequestration potential and associated partial C footprint. Calculated short-term C sequestration potentials were compared with long-term sequestration rates calculated from 95,214 producer soil samples collected between 1985 and 2010. National Agricultural Statistics Service (NASS) grain yields, measured root/shoot ratios and harvest indexes, soil organic C (SOC) and nonharvested C (NHC) first-order rate constants, measured SOC benchmarks [81,391 composite soil samples (0-15 cm) collected between 1985 and 1998], and 34,704 production surveys were used to calculate the short-term sequestration potentials. The SOC short-term, area weighted sequestration potential for the 2004 to 2007 time period was 181 kg C (ha * yr) -1. This relatively low rate was attributed to a drought that reduced the amount of NHC returned to soil. For the 2008 to 2010 time period, the area weighted short-term sequestration rate was 341 kg (ha * yr) -1. This rate was similar to the long-term measured rate of 368 kg C (ha * yr) -1. Findings from these independent SOC sequestration assessments supports the hypothesis that many of the regions surface soils are C sinks when seeded with corn. Based on short-term C sequestration rates, corn yields, and the corn conversion rate to ethanol, the area weighted surface SOC footprints for the 2004 to 2007 and 2008 to 2010 time periods was -10.4 and -15.4 g CO 2 equ MJ -1, respectively.