• Authors:
    • Brown, S.
    • Grimland, S.
    • Pearson, T. R. H.
  • Year: 2010
  • Summary: From exec summary: "....The basis of the direct and indirect emission calculations is a detailed empirical model that is discussed in the companion report to this work (hereafter referred to as the modified Bouwman model-MBM). The MBM incorporates various factors including quantity of fertilizer used, type of fertilizer, soil texture and drainage, pH and soil carbon concentration to predict nitrous oxide emissions. The companion report shows that the approach of the MBM is not sufficient at the project level, however, for a broad national analysis the approach is ideal....Our analysis resulted in an estimate of total annual N2O emission of 61 million tons of carbon dioxide equivalent for the three crops across the 31 states. Seventy percent of these emissions were from corn fields, 25% from wheat fields and 5% from cotton.
  • Authors:
    • Schlegel, A. J.
    • Stone, L. R.
  • Source: Agronomy Journal
  • Volume: 102
  • Issue: 2
  • Year: 2010
  • Summary: Efficient water use is the primary determinant of profitability in dryland crop production of the western Great Plains. For a sustainable increase in precipitation use efficiency (PUE) from that typical of the traditional winter wheat (Triticum aestivum L.)-fallow rotation with conventional stubble-mulch (sweep) tillage (CT) to occur, decreased use of fallow and tillage is required. Our objective was to quantify the effect of tillage intensity (no-till [NT], reduced tillage [RT], and CT) and phase of the winter wheat-grain sorghum [Sorghum bicolor (L.) Moench]-fallow rotation on selected sod properties that influence PUE, with emphasis on infiltration and the association between water-stable aggregates (WSA) and infiltration rate. Soil water content at -1.5 MPa matric potential, concentration of WSA >= 0.5 mm, mean weight diameter of WSA, and ponded steady-state infiltration rate were significantly greater with NT than RT or CT (infiltration rates: NT, 30.6; RT, 15.3; and CT, 11.4 mm h(-1)). Infiltration rate was significantly greater in the wheat phase (25.8 mm h(-1)) than in the sorghum (15.4 mm h(-1)) or fallow (16.2 mm h(-1)) phases. The significantly better conditions of aggregate stability and water infiltration with NT management and the lack of development of poor infiltration properties during the wheat season that would need to be alleviated by tillage after harvest reinforce the appropriateness of NT management in crop production systems of the region.
  • Authors:
    • van Groenigen, K. J.
    • van Kessel, C.
    • Oenema, O.
    • Velthof, G. L.
    • van Groenigen, J. W.
  • Source: European Journal of Soil Science
  • Volume: 61
  • Issue: 6
  • Year: 2010
  • Summary: Agricultural soils are the main anthropogenic source of nitrous oxide (N2O), largely because of nitrogen (N) fertilizer use. Commonly, N2O emissions are expressed as a function of N application rate. This suggests that smaller fertilizer applications always lead to smaller N2O emissions. Here we argue that, because of global demand for agricultural products, agronomic conditions should be included when assessing N2O emissions. Expressing N2O emissions in relation to crop productivity (expressed as above-ground N uptake: "yield-scaled N2O emissions") can express the N2O efficiency of a cropping system. We show how conventional relationships between N application rate, N uptake and N2O emissions can result in minimal yield-scaled N2O emissions at intermediate fertilizer-N rates. Key findings of a meta-analysis on yield-scaled N2O emissions by non-leguminous annual crops (19 independent studies and 147 data points) revealed that yield-scaled N2O emissions were smallest (8.4 g N2O-N kg-1N uptake) at application rates of approximately 180-190 kg Nha-1 and increased sharply after that (26.8 g N2O-N kg-1 N uptake at 301 kg N ha-1). If the above-ground N surplus was equal to or smaller than zero, yield-scaled N2O emissions remained stable and relatively small. At an N surplus of 90 kg N ha-1 yield-scaled emissions increased threefold. Furthermore, a negative relation between N use efficiency and yield-scaled N2O emissions was found. Therefore, we argue that agricultural management practices to reduce N2O emissions should focus on optimizing fertilizer-N use efficiency under median rates of N input, rather than on minimizing N application rates.
  • Authors:
    • Paré, D.
    • Angers, D. A.
    • Laganière, J.
  • Source: Global Change Biology
  • Volume: 16
  • Issue: 1
  • Year: 2010
  • Summary: Deforestation usually results in significant losses of soil organic carbon (SOC). The rate and factors determining the recovery of this C pool with afforestation are still poorly understood. This paper provides a review of the influence of afforestation on SOC stocks based on a meta-analysis of 33 recent publications (totaling 120 sites and 189 observations), with the aim of determining the factors responsible for the restoration of SOC following afforestation. Based on a mixed linear model, the meta-analysis indicates that the main factors that contribute to restoring SOC stocks after afforestation are: previous land use, tree species planted, soil clay content, preplanting disturbance and, to a lesser extent, climatic zone. Specifically, this meta-analysis (1) indicates that the positive impact of afforestation on SOC stocks is more pronounced in cropland soils than in pastures or natural grasslands; (2) suggests that broadleaf tree species have a greater capacity to accumulate SOC than coniferous species; (3) underscores that afforestation using pine species does not result in a net loss of the whole soil-profile carbon stocks compared with initial values (agricultural soil) when the surface organic layer is included in the accounting; (4) demonstrates that clay-rich soils (>33%) have a greater capacity to accumulate SOC than soils with a lower clay content (<33%); (5) indicates that minimizing preplanting disturbances may increase the rate at which SOC stocks are replenished; and (6) suggests that afforestation carried out in the boreal climate zone results in small SOC losses compared with other climate zones, probably because trees grow more slowly under these conditions, although this does not rule out gains over time after the conversion. This study also highlights the importance of the methodological approach used when developing the sampling design, especially the inclusion of the organic layer in the accounting.
  • Authors:
    • Gross, J. R.
    • Tanaka, D. L.
    • Liebig, M. A.
  • Source: Soil Science Society of America Journal
  • Volume: 74
  • Issue: 2
  • Year: 2010
  • Summary: The inclusion of cover crops during fallow (i.e., green fallow) may mitigate greenhouse gas (GHG) emissions from dryland cropping systems. An investigation was conducted to quantify the effects of chemical and green fallow on soil organic C (SOC) and CO2, CH4, and N2O flux within spring wheat (Triticum aestivum L.)-fallow (chemical fallow) and spring wheat-safflower (Carthamus tinctorius L.)-rye (Secale cereale L.) (green fallow) under no-till management in west-central North Dakota. Using static chamber methodology, flux measurements were made during 19 mo of the fallow period of each cropping system. Soil samples collected before initiation of flux measurements indicated no difference in SOC in the surface 10 cm between cropping systems. Additionally, differences in gas flux between cropping systems were few. Emission of CO2 was greater under green fallow than chemical fallow during spring thaw until the termination of rye (P = 0.0071). Uptake of atmospheric CH4 was the dominant exchange process during the evaluation period, and was significantly (P = 0.0124) greater under chemical fallow (-2.7 g CH4-C ha-1 d-1) than green fallow (-1.5 g CH4-C ha-1 d-1) following the termination of rye. Cumulative fluxes of CO2, CH4, and N2O did not differ between the chemical- and green-fallow phases during the 19-mo period (P = 0.1293, 0.2629, and 0.9979, respectively). The results from this evaluation suggest there was no net GHG benefit from incorporating a rye cover crop during the fallow phase of a dryland cropping system under no-till management.
  • Authors:
    • Yang, Z.
    • Chen, D.
    • Li, M.
    • Liang, W.
    • Wang, K.
    • Wang, Y.
    • Han, S.
    • Zhou, Z.
    • Zheng, X.
    • Liu, C.
  • Source: Plant and Soil
  • Volume: 332
  • Issue: 1-2
  • Year: 2010
  • Summary: Cotton is one of the major crops worldwide and delivers fibers to textile industries across the globe. Its cultivation requires high nitrogen (N) input and additionally irrigation, and the combination of both has the potential to trigger high emissions of nitrous oxide (N2O) and nitric oxide (NO), thereby contributing to rising levels of greenhouse gases in the atmosphere. Using an automated static chamber measuring system, we monitored in high temporal resolution N2O and NO fluxes in an irrigated cotton field in Northern China, between January 1st and December 31st 2008. Mean daily fluxes varied between 5.8 to 373.0 µg N2O-N m-2 h-1 and -3.7 to 135.7 µg NO-N m-2 h-1, corresponding to an annual emission of 2.6 and 0.8 kg N ha-1 yr-1 for N2O and NO, respectively. The highest emissions of both gases were observed directly after the N fertilization and lasted approximately 1 month. During this time period, the emission was 0.85 and 0.22 kg N ha-1 for N2O and NO, respectively, and was responsible for 32.3% and 29.0% of the annual total N2O and NO loss. Soil temperature, moisture and mineral N content significantly affected the emissions of both gases (p<0.01). Direct emission factors were estimated to be 0.95% (N2O) and 0.24% (NO). We also analyzed the effects of sampling time and frequency on the estimations of annual cumulative N2O and NO emissions and found that low frequency measurements produced annual estimates which differed widely from those that were based on continuous measurements.
  • Authors:
    • Saggar, S.
    • de Klein, C. A. M.
    • Ledgard, S. F.
    • Luo, J.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 136
  • Issue: 3-4
  • Year: 2010
  • Summary: Nitrous oxide (N2O) emissions from grazed pastures represent a significant source of atmospheric N2O. With an improved understanding and quantification of N sources, transformation processes, and soil and climatic conditions controlling N2O emissions, a number of management options can be identified to reduce N2O emissions from grazed pasture systems. The mitigation options discussed in this paper are: optimum soil management, limiting the amount of N fertiliser or effluent applied when soil is wet; lowering the amount of N excreted in animal urine by using low-N feed supplements as an alternative to fertiliser N-boosted grass; plant and animal selection for increased N use efficiency, using N process inhibitors that inhibit the conversion of urea to ammonium and ammonium to nitrate in soil; use of stand-off/feed pads or housing systems during high risk periods of N loss. The use of single or multiple mitigation options always needs to be evaluated in a whole farm system context and account for total greenhouse gas emissions including methane and carbon dioxide. They should focus on ensuring overall efficiency gains through decreasing N losses per unit of animal production and achieving a tighter N cycle. Whole-system life-cycle-based environmental analysis should also be conducted to assess overall environmental emissions associated the N2O mitigation options. (C) 2009 Elsevier B.V. All rights reserved.
  • Authors:
    • Sun, O. J.
    • Wang, E. L.
    • Luo, Z. K.
  • Source: Geoderma
  • Volume: 155
  • Issue: 3-4
  • Year: 2010
  • Summary: Soil is the largest reservoir of carbon (C) in the terrestrial biosphere and a slight variation in this pool could lead to Substantial changes in the atmospheric CO2 concentration, thus impact significantly on the global climate. Cultivation of natural ecosystems has led to marked decline in soil C storage, such that conservation agricultural practices (CAPs) are widely recommended as options to increase soil C storage, thereby mitigating climate change. In this review, we summarise soil C change as a result of cultivation worldwide and in Australia. We then combine the available data to examine the effects of adopting CAPs on soil C dynamics in Australian agro-ecosystems. Finally, we discuss the future research priorities related to soil C dynamics. The available data show that in Australian agro-ecosystems, cultivation has led to C loss for more than 40 years, with a total C loss of approximately 51% in the surface 0.1 m of soil. Adoption of CAPs generally increased soil C. Introducing perennial plants into rotation had the greatest potential to increase soil C by 18% compared with other CAPs. However, the same CAPS Could result in different outcomes on soil C under different climate and soil combinations. No consistent trend of increase in soil C was found with the duration of CAP applications, implying that questions remain regarding long-term impact of CAPs. Most of the available data in Australia are limited to the surface 0.1 to 0.3 m of soil. Efforts are needed to investigate soil C change in deeper soil layers in Order to understand the impact of crop root growth and various agricultural practices on C distribution in soil profile. Elevated atmospheric CO2 concentration, global warming and rainfall change Could all alter the C balance of agricultural soils. Because of the complexity of soil C response to management and environmental factors, a system modelling approach Supported by sound experimental data would provide the most effective means to analyse the impact of different management practices and future climate change on soil C dynamics. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.
  • Authors:
    • Sun, O. J.
    • Wang, E.
    • Luo, Z.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 139
  • Issue: 1-2
  • Year: 2010
  • Summary: Adopting no-tillage in agro-ecosystems has been widely recommended as a means of enhancing carbon (C) sequestration in soils. However, study results are inconsistent and varying from significant increase to significant decrease. It is unclear whether this variability is caused by environmental, or management factors or by sampling errors and analysis methodology. Using meta-analysis, we assessed the response of soil organic carbon (SOC) to conversion of management practice from conventional tillage (CT) to no-tillage (NT) based on global data from 69 paired-experiments, where soil sampling extended deeper than 40 cm. We found that cultivation of natural soils for more than 5 years, on average, resulted in soil C loss of more than 20 t ha-1, with no significant difference between CT and NT. Conversion from CT to NT changed distribution of C in the soil profile significantly, but did not increase the total SOC except in double cropping systems. After adopting NT, soil C increased by 3.15 +- 2.42 t ha-1 (mean ± 95% confidence interval) in the surface 10 cm of soil, but declined by 3.30 ± 1.61 t ha-1 in the 20-40 cm soil layer. Overall, adopting NT did not enhance soil total C stock down to 40 cm. Increased number of crop species in rotation resulted in less C accumulation in the surface soil and greater C loss in deeper layer. Increased crop frequency seemed to have the opposite effect and significantly increased soil C by 11% in the 0-60 cm soil. Neither mean annual temperature and mean annual rainfall nor nitrogen fertilization and duration of adopting NT affected the response of soil C stock to the adoption of NT. Our results highlight that the role of adopting NT in sequestrating C is greatly regulated by cropping systems. Increasing cropping frequency might be a more efficient strategy to sequester C in agro-ecosystems. More information on the effects of increasing crop species and frequency on soil C input and decomposition processes is needed to further our understanding on the potential ability of C sequestration in agricultural soils.
  • Authors:
    • MDEQ
    • Midwestern GHG Reduction Accord
  • Volume: 2010
  • Year: 2010
  • Summary: The Midwest Greenhouse Gas Reduction Accord (MGGRA) was a commitment by the governors of six Midwestern states and the premier of one Canadian province to reduce greenhouse gas (GHG) emissions through a regional cap-and-trade program and other complementary policy measures. The Accord was signed in November 2007 as a part of the Midwestern Governors Association Energy Security and Climate Change Summit. Though MGGRA has not been formally suspended, participating states are no longer pursuing it.