• Authors:
    • Herridge, D.
    • Guppy, C.
    • Begum, N.
    • Schwenke, G.
  • Source: Biology and Fertility of Soils
  • Volume: 50
  • Issue: 3
  • Year: 2014
  • Summary: Few studies have compared emissions of nitrous oxide (N2O), the potent greenhouse gas associated with decomposition of both below-ground (root) and above-ground (shoot) residues. We report a laboratory incubation experiment to evaluate effects of root and shoot residues from wheat, canola, soybean, and sorghum, incorporated into a naturally fertile acidic Black Vertisol, on N2O and carbon dioxide (CO2) emissions. The residue-amended Vertisol samples were incubated at 25 A degrees C and 70 % water-filled pore space (WFPS) to facilitate denitrification activity for a total period of 56 days. The incubated soils were periodically sampled for N2O, CO2, mineral N, and dissolved organic carbon (DOC). In general, shoot residues emitted more CO2 than roots, while N2O emissions were 50-70 % higher in cereal root residues than those in shoots. Surprisingly, the highest N2O emissions were associated with soils amended with the more inert high C/N ratio residues (wheat and sorghum roots), and to some extent, lowest emissions were associated with low C/N ratio (more labile) residues, particularly during the early stages of incubation (0-22 days). During this stage, there was a significant (p < 0.01) and negative correlation between N2O emissions and microbial respiration (CO2 efflux) and a positive (p < 0.001) correlation between microbial respiration and DOC. These results suggest that residue decomposition linked to N immobilization reduced N2O emissions during this early stage. Only, later in the study (23-56 days), did the high %N, low C/N ratio residues of soybean shoot and canola roots release at least twice as much N2O as the majority of the other treatments. We concluded that the unexpected patterns of N2O emissions were a result of the initially high mineral N content of the incubated soils and that root residues are likely to contribute substantially to emissions from cropping soils.
  • Authors:
    • Balarezo Giarola, N.
    • Tormena, C.
    • Ball, B.
    • da Silva, A.
    • Locks Guimaraes, R.
  • Source: Scientia Agricola
  • Volume: 71
  • Issue: 2
  • Year: 2014
  • Summary: No-tillage in Brazil is an efficient agricultural system that improves crop productivity whilst controlling erosion caused to the soil by degradation. However, there is some concern regarding soil compaction. Our objective was to determine whether the function of soil structure in sustaining crop growth was dependent on row and interrow positions in long-term no-tillage. We took soil samples from a field in a commercial farm under long-term no-tillage since 1979 on a clayey Oxisol in Southern Brazil. We assessed soil physical quality using the revised Peerlkamp technique and measured bulk density, air-filled porosity and air permeability of intact soil cores. Samples were incubated to assess in vitro N2O and CO2 production. The soil physical and structural properties showed consistent differences between interrow and row positions, where the properties measured were more favorable. The revised Peerlkamp technique proved as efficient as quantitative parameters in discriminating treatment differences. Overall, soil physical conditions in the interrow were less favourable than in the row. Pore continuity did not vary as regards position. This may explain why row position did not influence in vitro N2O and CO2 production. Soil physical quality under no-tillage system is enhanced, at least in the short term, by superficial disturbances in the row as a result of the action of the coulters of the no-tillage seeder.
  • Authors:
    • Sanabria, C.
    • Rodriguez, E.
    • Xiomara Pullido, S.
    • Loaiza, S.
    • del Pilar Hurtado, M.
    • Gutierrez, A.
    • Gomez, Y.
    • Chaparro, P.
    • Botero, C.
    • Bernal, J.
    • Arguello, O.
    • Rodriguez, N.
    • Lavelle, P.
    • Velasquez, E.
    • Fonte, S.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 185
  • Year: 2014
  • Summary: In the Orinoco River Basin of eastern Colombia large scale and rapid conversion of natural savannas into commercial agriculture exists as a critical threat for the ecological integrity of this fragile region. The highly acidic and compacted soils inherent to this region require thorough physical and chemical conditioning in order for intensive cropping systems to be established. Assessing the impact of this dramatic soil perturbation on biodiversity, ecosystem services and other elements of the natural capital is an urgent task for designing sustainable management options in the region. To address this need, we evaluated soil macro invertebrate communities and soil-based ecosystem services (climate regulation, hydrologic functions, soil stability provided by macro aggregation and nutrient provision potential) in four major production systems: improved pastures, annual crops (rice, corn and soy bean), oil palm and rubber plantations, and compared them to the original savanna. Fifteen plots of each system were sampled along a 200 km natural gradient of soil and climatic conditions. In each plot, we assessed climate regulation by measuring green house gas emissions (N2O, CH4 and CO2) and C storage in aboveground plant biomass and soil (0-20 cm). Soil biodiversity (macro invertebrate communities) and three other soil-based ecosystem services, were assessed using sets of 12-20 relevant variables associated with each service and synthesized via multivariate analyses into a single indicator for each ecosystem function, adjusted in a range of 0.1-1.0. Savannas yielded intermediate values for most indicators, while each production system appeared to improve at least one ecosystem service. For example, nutrient provision (chemical fertility) was highest in annual cropping systems (0.78 +/- 0.03) due to relatively high concentrations of Ca, Mg, N, K, and available P and low Al saturation. Hydrological functions and climate regulation (C storage and GHG emissions) were generally improved by perennial crops (oil palm and rubber), while indicators for macro invertebrate biodiversity and activity (0.73 +/- 0.05) and soil macro aggregation (0.76 +/- 0.02) were highest within improved pastures. High variability within each system indicates the potential to make improvements in fields with lowest indicator values, while differences among systems suggest the potential to mitigate negative impacts by combining plots with contrasted functions in a strategically designed landscape mosaic. (C) 2014 Elsevier B.V. All rights reserved.
  • Authors:
    • Robertson, R. D.
    • Mueller, C.
  • Source: Agricultural Economics
  • Volume: 45
  • Issue: 1
  • Year: 2014
  • Summary: Assessments of climate change impacts on agricultural markets and land-use patterns rely on quantification of climate change impacts on the spatial patterns of land productivity. We supply a set of climate impact scenarios on agricultural land productivity derived from two climate models and two biophysical crop growth models to account for some of the uncertainty inherent in climate and impact models. Aggregation in space and time leads to information losses that can determine climate change impacts on agricultural markets and land-use patterns because often aggregation is across steep gradients from low to high impacts or from increases to decreases. The four climate change impact scenarios supplied here were designed to represent the most significant impacts (high emission scenario only, assumed ineffectiveness of carbon dioxide fertilization on agricultural yields, no adjustments in management) but are consistent with the assumption that changes in agricultural practices are covered in the economic models. Globally, production of individual crops decrease by 10-38% under these climate change scenarios, with large uncertainties in spatial patterns that are determined by both the uncertainty in climate projections and the choice of impact model. This uncertainty in climate impact on crop productivity needs to be considered by economic assessments of climate change.
  • Authors:
    • Zimmerman, A. R.
    • Lal, R.
    • Mukherjee, A.
  • Source: Science of The Total Environment
  • Volume: 487
  • Issue: July
  • Year: 2014
  • Summary: Short and long-term impacts of biochar on soil properties under field conditions are poorly understood. In addition, there is a lack of field reports of the impacts of biochar on soil physical properties, gaseous emissions and C stability, particularly in comparison with other amendments. Thus, three amendments - biochar produced from oak at 650°C, humic acid (HA) and water treatment residual - (WTR) were added to a scalped silty-loam soil @ 0.5% (w/w) in triplicated plots under soybean. Over the 4-month active growing season, all amendments significantly increased soil pH, but the effect of biochar was the greatest. Biochar significantly increased soil-C by 7%, increased sub-nanopore surface area by 15% and reduced soil bulk density by 13% compared to control. However, only WTR amendment significantly increased soil nanopore surface area by 23% relative to the control. While total cumulative CH4 and CO2 emissions were not significantly affected by any amendment, cumulative N2O emission was significantly decreased in the biochar-amended soil (by 92%) compared to control over the growing period. Considering both the total gas emissions and the C removed from the atmosphere as crop growth and C added to the soil, WTR and HA resulted in net soil C losses and biochar as a soil C gain. However, all amendments reduced the global warming potential (GWP) of the soil and biochar addition even produced a net negative GWP effect. The short observation period, low application rate and high intra-treatment variation resulted in fewer significant effects of the amendments on the physicochemical properties of the soils than one might expect indicating further possible experimentation altering these variables. However, there was clear evidence of amendment-soil interaction processes affecting both soil properties and gaseous emissions, particularly for biochar, that might lead to greater changes with additional field emplacement time.
  • 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:
    • Cerri, C. C.
    • Bernoux, M.
    • Cerri, C. E. P.
    • Frazao, L. A.
    • Raucci, G. S.
    • Nunes Carvalho, J. L.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 183
  • Issue: January
  • Year: 2014
  • Summary: The objective of this study was to quantify the soil greenhouse gas (GHG) balance after the conversion of native vegetation (NV) to pasture and agricultural land and the conversion of agriculture to crop-pasture rotation (CPR) by evaluating changes in C stocks and N2O and CH4 fluxes. Soil sampling was carried out in March 2007 and April 2009 and GHG fluxes were sampled nine times between April 2007 and March 2009. The conversion of NV to pasture and agriculture decreased soil C stocks, with loss rates ranging from 0.25 to 0.64 Mg C ha(-1) yr(-1), respectively. The implementation of CPR in,agriculture areas increased soil C stocks by 0.60 Mg ha(-1) yr(-1). N2O emissions were higher in CPR and lower in NV. Emission of 1.03 kg CH4-C ha(-1) yr(-1) was observed in pasture, while in other areas consumption of CH4 was observed. The net GHG emission from the soil, including all GHG expressed in C-equivalent, indicated that the conversion of NV to pasture and agricultural land results in emissions of 0.54 and 0.72 Mg C ha(-1) yr(-1), respectively. In contrast, the adoption of CPR in areas under crop succession was a sink of 0.36 Mg ha(-1) yr(-1). Among the evaluated land use changes, only the implementation of CPR proved to be a good strategy to mitigate soil GHG emissions in Brazilian Cerrado. (C) 2013 Elsevier B.V. All rights reserved.
  • 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:
    • Skaracis, G. N.
    • Mariolis, N. A.
    • Vlachos, C. E.
  • Source: The Journal of Agricultural Science
  • Volume: 152
  • Issue: 2
  • Year: 2014
  • Summary: Sunflower (Helianthus annuus L.) and rapeseed (Brassica napus L.) are considered as the most suitable crops for biodiesel production in the Mediterranean basin. Soybean (Glycine max L.) could also be used, under certain conditions. In Greece, the farming practice adopted in each region varies significantly, leading to significant differences in the levels of emitted greenhouse gases (GHG). Greenhouse gas emissions were estimated during the cultivation phase as grams of carbon dioxide equivalents (g CO 2e) per megajoule (MJ), followed by emission savings (%) estimation when fossil fuels are replaced by biodiesel. Crop and region comparisons provided important information towards promoting sustainability. Overall, sunflower demonstrated the lowest average emissions, 53.8 g CO 2e/MJ, followed by rapeseed and soybean. Furthermore, rapeseed achieved the lowest emission saving level required by European legislation in most cases studied, with an average value of 37%. Irrigation and nitrogen fertilization were the operations mostly contributing to the total quantity of GHG emissions. More specifically, the highest GHG emissions were found for soybean irrigation (34%) and rapeseed nitrogen fertilization (68%).
  • Authors:
    • Schauer, R. L.
    • Griffing, E. M.
    • Rice, C. W.
  • Source: Journal of Environmental Quality
  • Volume: 43
  • Issue: 2
  • Year: 2014
  • Summary: Life cycle assessment is the predominant method to compare energy and environmental impacts of agricultural production systems. In this life cycle study, we focused on the comparison of swine manure to synthetic fertilizer as nutrients for corn production in Iowa. Deep pit (DP) and anaerobic lagoon (AL) treatment systems were compared separately, and urea ammonium nitrate (UAN) was chosen as the representative synthetic fertilizer. The two functional units used were fertilization of 1000 kg of corn in a continuous corn system and fertilization of a crop yielding 1000 kg of corn and a crop yielding 298 kg of soybean in a 2-yr corn-soybean rotation. Iowa-specific versions of emission factors and energy use were used when available and compared with Intergovernmental Panel on Climate Change values. Manure was lower than synthetic fertilizer for abiotic depletion and about equal with respect to eutrophication. Synthetic fertilizer was lower than manure for global warming potential (GWP) and acidification. The choice of allocation method and life cycle boundary were important in understanding the context of these results. In the DP system, methane (CH 4) from housing was the largest contributor to the GWP, accounting for 60% of the total impact. When storage systems were compared, the DP system had 50% less GWP than the AL system. This comparison was due to reduction in CH 4 emissions from the storage system and conservation of nitrogen. Nitrous oxide emissions were the biggest contributor to the GWP of UAN fertilization and the second biggest contributor to the GWP of manure. Monte Carlo and scenario analyses were used to test the robustness of the results and sensitivity to methodology and important impact factors. The available crop-land and associated plant nutrient needs in Iowa was compared with manure production for the current hog population. On a state- or county-wide level, there was generally an excess of available land. On a farm level, there is often an excess of manure, which necessitates long-distance transport.