• Authors:
    • Committee on the Impact of Biotechnology on Farm-Level Economics and Sustainability
    • National Research Council
  • Year: 2010
  • Authors:
    • Pollack, A.
    • Neuman, W.
  • Source: The New York Times
  • Volume: 4 May
  • Year: 2010
  • Summary: A 2010 article in the New York times about Round-Up resistant weeds in the United States.
  • Authors:
    • Hatfield, J. L.
    • Parkin, T. B.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 136
  • Issue: 1-2
  • Year: 2010
  • Summary: Fertilizer application in crop production agriculture has been identified as a major source of the greenhouse gas nitrous oxide. Thus, management strategies that increase fertilizer N use efficiency will reduce N2O emission. Anhydrous ammonia applied to cropland in the fall is recognized as a management practice that increases the risk of N loss from the rooting zone, however, this practice is still common in the U.S. Midwest Corn Belt. The nitrification inhibitor, nitrapyrin has been shown to decrease soil N losses during the fall and spring, and maintain fertilizer N availability to the crop. Additionally, nitrification inhibitors have shown promise in reducing soil N2O emissions. However, there have been no studies evaluating the effectiveness of nitrapyrin to reduce annual N2O emissions from land receiving fall-applied anhydrous ammonia. This study was conducted over 2 years to measure N2O emissions from corn plots with fall-applied anhydrous ammonia with and without nitrapyrin. Based on soil NO3 and NH4 analyses, we observed that nitrapyrin delayed nitrification, and in 1 year, reduced late fall/early spring N2O emission. However, annual N2O emissions were not significantly reduced. Significantly higher corn grain yields were observed in the nitrapyrin treatment in both years.
  • 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:
    • Conway, R.
    • Noe, S.
    • Schwartz, R.
    • Nefstead, W.
    • Gallagher, P.W.
    • Shapouri, H.
  • Year: 2010
  • Summary: The Agricultural Resource Management Survey of corn growers for the year 2005 and the 2008 survey of dry mill ethanol plants are used to estimate the net energy balance of corn ethanol. This report measures all conventional fossil fuel energy used in the production of 1 gallon of corn ethanol. The ratio is about 2.3 BTU of ethanol for 1 BTU of energy inputs, when a portion of total energy input is allocated to byproduct, and fossil fuel is used for processing energy. The ratio is somewhat higher for some firms that are partially substituting biomass energy in processing energy.
  • 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:
    • Ochsner, T. E.
    • Venterea, R. T.
  • Source: Soil Science Society of America Journal
  • Volume: 74
  • Issue: 2
  • Year: 2010
  • Summary: Quantifying N2O emissions from corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] fields under different fertilizer regimes is essential to developing national inventories of greenhouse gas emissions. The objective of this study was to compare N2O emissions in plots managed for more than 15 yr under continuous corn (C/C) vs. a corn-soybean (C/S) rotation that were fertilized during the corn phase with either anhydrous NH3 (AA) or urea (U). During three growing seasons, N2O emissions from corn following corn were nearly identical to corn following soybean. In both systems, however, N2O emissions with AA were twice the emissions with U. After accounting for N2O emissions during the soybean phase, it was estimated that a shift from C/S to C/C would result in an increase in annual emissions of 0.78 kg N ha-1 (equivalent to 0.11 Mg CO2-C ha-1) when AA was used, compared with only 0.21 kg N ha-1 (0.03 Mg CO2-C ha-1) with U. In light of trends toward increased use of U, these results suggest that fertilizer-induced soil N2O emissions may decline in the future, at least per unit of applied N, although further study is needed in different soils and cropping systems. While soil CO2 emissions were 20% higher under C/C, crop residue from the prior year did not affect soil inorganic N or dissolved organic C during the subsequent season. We also compared different flux-calculation schemes, including a new method for correcting chamber-induced errors, and found that selection of a calculation method altered N2O emissions estimates by as much as 35%.
  • Authors:
    • Barbour, N.
    • Archer, D. W.
    • Johnson, J. M. F.
  • Source: Soil Science Society of America Journal
  • Volume: 74
  • Issue: 2
  • Year: 2010
  • Summary: The agricultural sector is a small but significant contributor to the overall anthropogenic greenhouse gas (GHG) emission and a major contributor of N2O emission in the United States. Land management practices or systems that reduce GHG emission would aid in slowing climate change. We measured the emission of CO2, CH4, and N2O from three management scenarios: business as usual (BAU), maximum C sequestration (MAXC), and optimum greenhouse gas benefits (OGGB). The BAU scenario was chisel or moldboard plowed, fertilized, in a 2-yr rotation (corn [Zea mays L.]-soybean [Glycine max (L.) Merr]). The MAXC and OGGB scenarios were strip tilled in a 4-yr rotation (corn-soybean-wheat [Triticum aestivum L.]/alfalfa [Medicago sativa L.]-alfalfa). The MAXC received fertilizer inputs but the OGGB scenario was not fertilized. Nitrous oxide, CO2, and CH4 emissions were collected using vented static chambers. Carbon dioxide flux increased briefly following tillage, but the impact of tillage was negligible when CO2 flux was integrated across an entire year. The sod tended to be neutral to a slight CH4 sink under these managements scenarios. The N2O flux during spring thaw accounted for up to 65% of its annual emission, compared with 6% or less due to application of N fertilizer. Annual cumulative emissions of CO2, CH4, and N2O did not vary significantly among these three management scenarios. Reducing tillage and increasing the length of the crop rotation did not appreciably change GHG emissions, Strategies that reduce N2O flux during spring thaw could reduce annual N2O emission.
  • 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:
    • Stewart, G.
    • Gregorich, E. G.
    • McLaughlin, N. B.
    • Morrison, M. J.
    • Deen, W.
    • Tremblay, N.
    • Wu, T. Y.
    • Ma, B. L.
  • Source: Global Change Biology
  • Volume: 16
  • Issue: 1
  • Year: 2010
  • Summary: Nitrogen fertilization is considered as an important source of atmospheric N2O emission. A seven site-year on-farm field experiment was conducted at Ottawa and Guelph, ON and Saint-Valentin, QC, Canada to characterize the affect of the amount and timing of N fertilizer on N2O emission in corn (Zea mays L.) production. Using the static chamber method, gas samples were collected for 28-days after preplant and 28-days after sidedress fertilization at the seven site-year, resulting in 14 monitoring periods. For both methods of fertilization, peak N2O flux and cumulative emission increased with the amount of N applied, with rates ranging from 30 to 900 mu g N m(-2) h(-1). Depending on N amount and time of application, cumulative emission varied from 0.05 to 2.42 kg N ha(-1), equivalent to 0.03% to 1.45% of the N fertilizer applied. Differences in N2O emission peaks among fertilizer treatments were clearly separated in 13 out of 14 monitoring periods. Total N2O emissions may have been underestimated compared with annual monitoring in 10 out of the 49 cases because the monitoring period ended before N2O efflux returned to the baseline level. The flux of N2O was negligible when soil mineral N in the 0-15 cm layer was 15 degrees C was likely the driving force responsible for the higher levels of N2O found for sidedress than preplant application methods. However, caution must be taken when interpreting these later results as preplant fertilization may have continuously stimulated N2O emissions after the 28-days monitoring period, especially in situations where N2O effluxes have not fallen back to their baseline levels. Increasing fertilizer rates from 90 to 150 kg N ha(-1) resulted in slight increases in yields, but doubled cumulative N2O emissions.