• Authors:
    • Roberts, T. L.
  • Source: Turkish Journal of Agriculture and Forestry
  • Volume: 32
  • Year: 2008
  • Summary: Public interest and awareness of the need for improving nutrient use efficiency is great, but nutrient use efficiency is easily misunderstood. Four indices of nutrient use efficiency are reviewed and an example of different applications of the terminology show that the same data set might be used to calculate a fertilizer N efficiency of 21% or 100%. Fertilizer N recovery efficiencies from researcher managed experiments for major grain crops range from 46% to 65%, compared to on-farm N recovery efficiencies of 20% to 40%. Fertilizer use efficiency can be optimized by fertilizer best management practices that apply nutrients at the right rate, time, and place. The highest nutrient use efficiency always occurs at the lower parts of the yield response curve, where fertilizer inputs are lowest, but effectiveness of fertilizers in increasing crop yields and optimizing farmer profitability should not be sacrificed for the sake of efficiency alone. There must be a balance between optimal nutrient use efficiency and optimal crop productivity.
  • Authors:
    • Bertrand, N.
    • Chantigny, M. H.
    • Angers, D. A.
    • Rochette, P.
  • Source: Soil Science Society of America Journal
  • Volume: 72
  • Issue: 5
  • Year: 2008
  • Summary: The anticipated benefits of increased soil C stocks on net soil-surface greenhouse gas (GHG) emissions after adoption of soil conservation practices can be offset by increases in soil N2O emissions. The objective of this study was to assess the short-term impacts of no-till (NT) on soil N2O emissions. The study was conducted in eastern Canada in the 3rd, 4th, and 5th yr after initiation of NT and fall moldboard plowing (MP) on heavy clay and gravelly loam soils. Annual emissions of N2O were exceptionally high in the heavy clay soil, varying from 12 to 45 kg N2O-N ha-1 during the 3 yr of the study. Such high emissions were probably not associated with fertilizer N inputs but rather with denitrification sustained by the decomposition of large soil organic matter stocks (192 Mg C ha-1 in the top 0.5 m). On average, NT more than doubled N2O emissions compared with MP in the heavy clay soil. The influence of plowing on N2O flux in the heavy clay soil was probably the result of increased soil porosity that maintained soil aeration and water content at levels restricting denitrification and N2O production in the top 0.20 m. In the loam soil, average emissions during the 3 yr were similar in the NT and MP plots. The results of this study indicate that the potential of NT for decreasing net GHG emissions may be limited in fine-textured soils rich in organic matter that are prone to high water content and reduced aeration.
  • Authors:
    • Desjardins, R. L.
    • Wagner-Riddle, C.
    • Pennock, D. J.
    • McConkey, B. G.
    • Lemke, R. L.
    • Worth, D. E.
    • Rochette, P.
  • Source: Canadian Journal of Soil Science
  • Volume: 88
  • Issue: 5
  • Year: 2008
  • Summary: International initiatives such as the United Nations Framework Convention on Climate Change and the Kyoto Protocol require that countries calculate national inventories of their greenhouse gas emissions. The objective of the present study was to develop a country-specific (Tier II) methodology to calculate the inventory of N2O emissions from agricultural soils in Canada. Regional fertilizer-induced emission factors (EFreg) were first determined using available field experimental data. Values for EFreg were 0.0016 kg N2O-N kg-1 N in the semi-arid Brown and 0.008 kg N2O-N kg N-1 in the sub-humid Black soil zones of the Prairie region, and 0.017 kg N2O-N kg-1 N in the humid provinces of Quebec and Ontario. A function relating EFreg to the "precipitation to potential evapotranspiration" ratio was determined to estimate annual emission factors (EFeco) at the ecodistrict scale in all agricultural regions of Canada. Country-specific coefficients were also developed to account for the effect of several additional factors on soil N2O emissions. Emissions from fine-textured soils were estimated as being 50% greater than from coarse- and medium-textured soils in eastern Canada; emissions during winter and spring thaw corresponded to 40% of emissions during the snow-free season in eastern Canada; increased emissions from lower (wetter) sections of the landscape and irrigated areas were accounted for; emissions from no-till soils were 10% greater in eastern, but 20% lower in western Canada than from those under conventional tillage practices; emissions under summerfallow were estimated as being equal to those from soils under annual cropping. This country-specific methodology therefore accounts for regional climatic and land use impacts on N2O emission factors, and includes several sources/offsets that are not included in the Intergovernmental Panel on Climate Change (IPCC) default approach.
  • Authors:
    • Stevens, W. B.
    • Jabro, J. D.
    • Sainju, U. M.
  • Source: Journal of Environmental Quality
  • Volume: 37
  • Issue: 1
  • Year: 2008
  • Summary: Management practices can influence soil CO2 emission and C content in cropland, which can effect global warming. We examined the effects of combinations of irrigation, tillage, cropping systems, and N fertilization on soil CO2 flux, temperature, water, and C content at the 0- to 20-cm depth from May to November 2005 at two sites in the northern Great Plains. Treatments were two irrigation systems (irrigated vs. non-irrigated) and six management practices that contained tilled and no-tilled malt barley (Hordeum vulgaris L.) with 0 to 134 kg N ha-1, no-tilled pea (Pisum sativum L.), and a conservation reserve program (CRP) planting applied in Lihen sandy loam (sandy, mixed, frigid, Entic Haplustolls) in western North Dakota. In eastern Montana, treatments were no-tilled malt barley with 78 kg N ha-1, no-tilled rye (Secale cereale L.), no-tilled Austrian winter pea, no-tilled fallow, and tilled fallow applied in dryland Williams loam (fine-loamy, mixed Typic Argiborolls). Irrigation increased CO2 flux by 13% compared with non-irrigation by increasing soil water content in North Dakota. Tillage increased CO2 flux by 62 to 118% compared with no-tillage at both places. The flux was 1.5- to 2.5-fold greater with tilled than with non-tilled treatments following heavy rain or irrigation in North Dakota and 1.5- to 2.0-fold greater with crops than with fallow following substantial rain in Montana. Nitrogen fertilization increased CO2 flux by 14% compared with no N fertilization in North Dakota and cropping increased the flux by 79% compared with fallow in no-till and 0 kg N ha-1 in Montana. The CO2 flux in undisturbed CRP was similar to that in no-tilled crops. Although soil C content was not altered, management practices influenced CO2 flux within a short period due to changes in soil temperature, water, and nutrient contents. Regardless of irrigation, CO2 flux can be reduced from croplands to a level similar to that in CRP planting using no-tilled crops with or without N fertilization compared with other management practices.
  • Authors:
    • Martius, C.
    • Lamers, J. P. A.
    • Ibragimov, N.
    • Kienzler, K.
    • Wassmann, R.
    • Scheer, C.
  • Source: Global Change Biology
  • Volume: 14
  • Issue: 10
  • Year: 2008
  • Summary: Land use and agricultural practices can result in important contributions to the global source strength of atmospheric nitrous oxide (N2O) and methane (CH4). However, knowledge of gas flux from irrigated agriculture is very limited. From April 2005 to October 2006, a study was conducted in the Aral Sea Basin, Uzbekistan, to quantify and compare emissions of N2O and CH4 in various annual and perennial land-use systems: irrigated cotton, winter wheat and rice crops, a poplar plantation and a natural Tugai (floodplain) forest. In the annual systems, average N2O emissions ranged from 10 to 150 mu g N2O-N m(-2) h(-1) with highest N2O emissions in the cotton fields, covering a similar range of previous studies from irrigated cropping systems. Emission factors (uncorrected for background emission), used to determine the fertilizer-induced N2O emission as a percentage of N fertilizer applied, ranged from 0.2% to 2.6%. Seasonal variations in N2O emissions were principally controlled by fertilization and irrigation management. Pulses of N2O emissions occurred after concomitant N-fertilizer application and irrigation. The unfertilized poplar plantation showed high N2O emissions over the entire study period (30 mu g N2O-N m(-2) h(-1)), whereas only negligible fluxes of N2O (< 2 mu g N2O-N m(-2) h(-1)) occurred in the Tugai. Significant CH4 fluxes only were determined from the flooded rice field: Fluxes were low with mean flux rates of 32 mg CH4 m(-2) day(-1) and a low seasonal total of 35.2 kg CH4 ha(-1). The global warming potential (GWP) of the N2O and CH4 fluxes was highest under rice and cotton, with seasonal changes between 500 and 3000 kg CO2 eq. ha(-1). The biennial cotton-wheat-rice crop rotation commonly practiced in the region would average a GWP of 2500 kg CO2 eq. ha(-1) yr(-1). The analyses point out opportunities for reducing the GWP of these irrigated agricultural systems by (i) optimization of fertilization and irrigation practices and (ii) conversion of annual cropping systems into perennial forest plantations, especially on less profitable, marginal lands.
  • Authors:
    • Snyder, C. S.
  • Year: 2008
  • Summary: The discussion and guides that follow are oriented toward the central U.S. Corn Belt, but are relevant to other cropping systems with similar crop geographies. They are provided to assist in fertilizer nitrogen (N) management decisions that will help lessen the impact of fertilizer N use on greenhouse gas (GHG) emissions and help mitigate the global warming potential (GWP) - expressed as CO2 equivalent. The three GHGs of interest to agriculture are: nitrous oxide (N2O), methane (CH4), and CO2. The GWP of CH4 is 23 times greater and the GWP of N2O is 296 times greater than that of CO2. Because fertilizer N use may be associated with N2O emissions, and because the GWP of N2O is so much greater than CO2, fertilizer N BMPs to reduce N2O emissions are emphasized in this practical guide. For example, fertilizer N BMPs which help minimize excess nitrate (NO3 -) in the soil during warm, wet, or waterlogged conditions can result in lowered risks for N2O emission.
  • Authors:
    • Snyder, K.
    • Sims, P. L.
    • Schuman, G. E.
    • Saliendra, N. Z.
    • Morgan, J. A.
    • Mielnick, P.
    • Mayeux, H.
    • Johnson, D. A.
    • Haferkamp, M.
    • Gilmanov, T. G.
    • Frank, A. B.
    • Emmerich, W.
    • Dugas, W.
    • Bradford, J. A.
    • Angell, R.
    • Svejcar, T.
  • Source: Rangeland Ecology & Management
  • Volume: 61
  • Issue: 5
  • Year: 2008
  • Summary: Rangelands account for almost half of the earth's land surface and may play an important role in the global carbon (C) cycle. We Studied net ecosystem exchange (NEE) of C on eight North American rangeland sites over a 6-yr period. Management practices and disturbance regimes can influence NEE; for consistency, we compared ungrazed and undisturbed rangelands including four Great Plains sites from Texas to North Dakota, two Southwestern hot desert sites in New Mexico and Arizona, and two Northwestern sagebrush steppe sites in Idaho and Oregon. We used the Bowen ratio-energy balance system for continuous measurements of energy, water vapor, and carbon dioxide (CO2) fluxes at each study site during the measurement period (1996 to 2001 for most sites). Data were processed and screened using standardized procedures, which facilitated across-location comparisons. Although almost any site could be either a sink or source for C depending on yearly weather patterns, five of the eight native rangelands typically were sinks for atmospheric CO2 during the study period. Both sagebrush steppe sites were sinks and three of four Great Plains grasslands were sinks, but the two Southwest hot desert sites were sources of C on an annual basis. Most rangelands were characterized by short periods of high C uptake (2 mo to 3 mo) and long periods of C balance or small respiratory losses of C. Weather patterns during the measurement period strongly influenced conclusions about NEE on any given rangeland site. Droughts tended to limit periods of high C uptake and thus cause even the most productive sites to become sources of C on an annual basis. Our results show that native rangelands are a potentially important terrestrial sink for atmospheric CO2, and maintaining the period of active C uptake will be critical if we are to manage rangelands for C sequestration.
  • Authors:
    • Li, X.
    • Flesch, T. K.
    • Gao, Z.
    • Desjardins, R. L.
    • van Haarlem, R. P.
  • Source: Canadian Journal of Animal Science
  • Volume: 88
  • Issue: 4
  • Year: 2008
  • Summary: Methane and ammonia emissions from a beef feedlot in western Canada for a twelve-day period in the fall. Can. J. Anim. Sci. 88: 641649. Commercial feedlot operations are becoming a mainstay in the Canadian beef industry. These large operations that typically raise thousands of animals at a time represent a large localized source of methane (CH4) and of atmospheric pollutants such as ammonia (NH3) and particulate matter. An inverse dispersion model was utilized to calculate CH4 and NH3 emissions from a commercial cattle feedlot and an adjacent runoff retention pond. The feedlot measurements were collected within the interior of the feedlot enabling a near continuous emissions record over the 12 d of the study period. Average daily emission estimates of CH4 and NH3 were 323 and 318 g animal -1d-1, respectively. The CH4 emissions represent 4% of the gross energy intake (GEI) and NH3 emissions represent 72% of the total N intake. Emissions from the runoff retention pond associated directly with the feedlot operation were approximately 2.7 and 2% of the daily average feedlot emissions of CH4 and NH3, respectively.
  • Authors:
    • Stanenas, Adam J.
    • Venterea, Rodney T.
  • Source: Journal of Environmental Quality
  • Volume: 37
  • Issue: 4
  • Year: 2008
  • Summary: The impact of no-till (NT) and other reduced tillage (RT) practices on soil to atmosphere fluxes of nitrous oxide (N2O) are difficult to predict, and there is limited information regarding strategies for minimizing fluxes from RT systems. We measured vertical distributions of key microbial, chemical, and physical properties in soils from a long-term tillage experiment and used these data as inputs to a process-based model that accounts for N2O production, consumption, and gaseous diffusion. The results demonstrate how differences among tillage systems in the stratification of microbial enzyme activity chemical reactivity, and other properties can control NO fluxes. Under nitrification-dominated conditions, simulated N2O emissions in the presence of nitrite (NO2-) were 2 to 10 times higher in NT soil compared to soil under conventional tillage (CT). Under denitrification-dominated conditions in the presence of nitrate (NO3-), higher bulk density and water content under NT promoted higher denitrification rates than CT. These effects were partially offset by higher soluble organic carbon and/or temperature and lower N2O reduction rates under CT. The NT/CT ratio of N2O fluxes increased as NO2- or NO3- was placed closer to the surface. The highest NT/CT ratios of N2O flux (> 30:1) were predicted for near-surface NO3- placement, while NT/CT ratios < 1 were predicted for NO3- placement below 15 cm. These results suggest that N2O fluxes from RT systems can be minimized by subsurface fertilizer placement and by using a chemical form of fertilizer that does not promote substantial NO2- accumulation.
  • Authors:
    • Worth, D.
    • Desjardins, R. L.
    • Dyer, J. A.
    • VergĂ©, X. P. C.
  • Source: Agricultural Systems
  • Volume: 98
  • Issue: 2
  • Year: 2008
  • Summary: Commodity-specific estimates of the greenhouse gas (GHG) emissions from Canadian agriculture are required in order to identify the most efficient GHG mitigation measures. In this paper, the methodology from the Intergovernmental Panel on Climate Change (IPCC) for estimating bovine GHG emissions, for census years from 1981 to 2001, was applied to the Canadian beef industry. This analysis, which is based on several adaptations of IPCC methodology already done for the Canadian dairy industry, includes the concept of a beef crop complex, the land base that feeds the beef population, and the use of recommendations for livestock feed rations and fertilizer application rates to down-scale the national area totals of each crop, regardless of the use of that crop, to the feed requirements of the Canada's beef population. It shows how high energy feeds are reducing enteric methane emissions by displacing high roughage diets. It also calculates an emissions intensity indicator based on the total weight of live beef cattle destined for market. While total GHG from Canadian beef production have increased from 25 to 32 Tg of CO2 equiv. between 1981 and 2001, this increase was mainly driven by expansion of the Canadian cattle industry. The emission intensity indicator showed that between 1981 and 2001, the Canadian beef industry GHG emissions per kg of live animal weight produced for market decreased from 16.4 to 10.4 kg of CO2 equiv.