• 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:
    • Li, C.
    • Drury, C. F.
    • Rochette, P.
    • Desjardins, R. L.
    • Grant, B. B.
    • Smith, W. N.
  • Source: Canadian Journal of Soil Science
  • Volume: 88
  • Issue: 2
  • Year: 2008
  • Summary: Process-based models play an important role in the estimation of soil N2O emissions from regions with contrasting soil and climatic conditions. A study was performed to evaluate the ability of two process-based models, DAYCENT and DNDC, to estimate N2O emissions, soil nitrate- and ammonium-N levels, as well as soil temperature and water content. The measurement sites included a maize crop fertilized with pig slurry (Quebec) and a wheat-maize-soybean rotation as part of a tillage-fertilizer experiment (Ontario). At the Quebec site, both models accurately simulated soil temperature with an average relative error (ARE) ranging from 0 to 2%. The models underpredicted soil temperature at the Ontario site with ARE from -5 to -7% for DNDC and from -5 to -13% for DAYCENT. Both models underestimated soil water content particularly during the growing season. The DNDC model accurately predicted average seasonal N2O emissions across treatments at both sites whereas the DAYCENT model underpredicted N2O emissions by 32 to 58% for all treatments excluding the fertilizer treatment at the Quebec site. Both models had difficulty in simulating the timing of individual emission events. The hydrology and nitrogen transformation routines need to be improved in both models before further enhancements are made to the trace gas routines.
  • Authors:
    • Toderi, G.
    • Baldoni, G.
    • Comellini, F.
    • Giordani, G.
    • Nastri, A.
    • Triberti, L.
  • Source: European Journal of Agronomy
  • Volume: 29
  • Issue: 1
  • Year: 2008
  • Summary: The soil organic matter content represents a huge reservoir of plant nutrients and an effective safeguard against pollution; beside it can sequestrate atmospheric CO2. Since 1966 up to now in the Southeast Po valley (Italy), the soil organic C (SOC) and total N (TN) dynamics in the 0-0.40 m soil layer under a maize-wheat rainfed rotation are studied as influenced by organic and mineral N fertilizations. Every year in the same plots cattle manure, cattle slurry, and crop residues (i.e. wheat straw and maize stalk) are ploughed under to 0.40 m depth at a same dry matter rate (6.0 and 7.5 t DM ha-1 year-1 wheat and maize, respectively) and are compared to an unamended control. Each plot is splitted to receive four rates of mineral fertilizer (0-100-200-300 kg N ha-1). In the whole experiment, in 2000 SOC concentration was lower than in 1966 (6.77 and 7.72 g kg-1, respectively), likely for the deeper tillage that diluted SOC and favoured mineralization in deeper soil layer. From 1972 to 2000 SOC stock did not change in the control and N fertilized plots, while it increased at mean rates of 0.16, 0.18, and 0.26 t ha-1 year-1 with the incorporation of residues, slurry and manure, corresponding to sequestration efficiencies of 3.7, 3.8 and 8.1% of added C with the various materials. TN followed the same SOC dynamic, demonstrating how it depends on the soil organic matter. Manure thus confirmed its efficacy in increasing both SOC content and soil fertility on the long-term. In developed countries, however, this material has become scarcely available; slurry management is expensive and implies high environmental risks. Moreover, in a C balance at a farm (or regional) scale, the CO2 lost during manure and slurry stocking should be considered. For these reasons, the incorporation of cereal residues, even if only a little of their C content was found capable of soil accumulation, appears the best way to obtain a significant CO2 sequestration in developed countries. Our long-term experiment clearly shows how difficult it is to modify SOC content. Moreover, because climate and soil type can greatly influence SOC dynamic, to increase CO2 sequestration in cropland, it is important to optimize the fertilization within an agricultural management that includes all the agronomic practices (e.g. tillage, water management, cover crops, etc.) favouring the organic matter build up in the soil.
  • Authors:
    • Trostle, R.
  • Source: USDA, Economic Research Service
  • Year: 2008
  • Summary: This 2008 report, from the USDA's Economic Research Service, discusses factors contributing to the recent increase in food commodity prices.
  • Authors:
    • Diamant, A.
    • Knipping, E.
  • Source: Handout for US EPA Integrated Nitrogen Committee
  • Year: 2008
  • Authors:
    • McLaughlin, N. B.
    • Reynolds, W. D.
    • Yang, X. M.
    • Drury, C. F.
  • Source: Canadian Journal of Soil Science
  • Volume: 88
  • Issue: 2
  • Year: 2008
  • Summary: t is well established that nitrous oxide (N2O) and carbon dioxide (CO2) emissions from agricultural land are influenced by the type of crop grown, the form and amount of nitrogen (N) applied, and the soil and climatic conditions under which the crop is grown. Crop rotation adds another dimension that is often overlooked, however, as the crop residue being decomposed and supplying soluble carbon to soil biota is usually from a different crop than the crop that is currently growing. Hence, the objective of this study was to compare the influence of both the crop grown and the residues from the preceding crop on N2O and CO2 emissions from soil. In particular, N2O and CO2 emissions from monoculture cropping of corn, soybean and winter wheat were compared with 2-yr and 3-yr crop rotations (corn-soybean or corn-soybean-winter wheat). Each phase of the rotation was measured each year. Averaged over three growing seasons (from April to October), annual N2O emissions were about 3.1 to 5.1 times greater in monoculture corn (2.62 kg N ha-1 ) compared with either monoculture soybean (0.84 kg N ha-1) or monoculture winter wheat (0.51 kg N ha-1). This was due in part to the higher inorganic N levels in the soil resulting from the higher N application rate with corn (170 kg N ha-1) than winter wheat (83 kg N ha-1) or soybean (no N applied). Further, the previous crop also influenced the extent of N2O emissions in the current crop year. When corn followed corn, the average N2O emissions (2.62 kg N ha1 ) were about twice as high as when corn followed soybean (1.34 kg N ha-1) and about 60% greater than when corn followed winter wheat (1.64 kg N ha-1). Monoculture winter wheat had about 45% greater CO2 emissions than monoculture corn or 51% greater emissions than monoculture soybean. In the corn phase, CO2 emissions were greater when the previous crop was winter wheat (5.03 t C ha-1) than when it was soybean (4.20 t C ha-1) or corn (3.91 t C ha-1). Hence, N2O and CO2 emissions from agricultural fields are influenced by both the current crop and the previous crop, and this should be accounted for in both estimates and forecasts of the emissions of these important greenhouse gases.
  • Authors:
    • Wallander, R.
    • Lemke, R. L.
    • Miller, P. R.
    • Engel, R. E.
    • Dusenbury, M. P.
  • Source: Journal of Environmental Quality
  • Volume: 37
  • Issue: 2
  • Year: 2008
  • Summary: Field measurements of N2O emissions from soils are limited for cropping systems in the semiarid northern Great Plains (NGP). The objectives were to develop N2O emission-time profiles for cropping systems in the semiarid NGP, define important periods of loss, determine the impact of best management practices on N2O losses, and estimate direct N fertilizer-induced emissions (FIE). No-till (NT) wheat (Triticum Aestivum L.)-fallow, wheat-wheat, and wheat-pea (Pisum sativum), and conventional till (CT) wheat-fallow, all with three N regimes (200 and 100 kg N ha-1 available N, unfertilized control); plus a perennial grass-alfalfa (Medicago sativa L.) system were sampled over 2 yr using vented chambers. Cumulative 2-yr N2O emissions were modest in contrast to reports from more humid regions. Greatest N2O flux activity occurred following urea-N fertilization (10-wk) and during freeze-thaw cycles. Together these periods comprised up to 84% of the 2-yr total. Nitrification was probably the dominant process responsible for N2O emissions during the post-N fertilization period, while denitrification was more important during freeze-thaw cycles. Cumulative -yr N2O-N losses from fertilized regimes were greater for wheat-wheat (1.31 kg N ha-1) than wheat-fallow (CT and NT) (0.48 kg N ha-1), and wheat-pea (0.71 kg N ha-1) due to an additional N fertilization event. Cumulative losses from unfertilized cropping systems were not different from perennial grass-alfalfa (0.28 kg N ha-1). Tillage did not affect N2O losses for the wheat-fallow systems. Mean FIE level was equivalent to 0.26% of applied N, and considerably below the Intergovernmental Panel on Climate Change mean default value (1.25%).
  • Authors:
    • Lehmann, J.
    • Gaunt, J. L.
  • Source: Environmental Science & Technology
  • Volume: 42
  • Issue: 11
  • Year: 2008
  • Summary: Compared to its use as an energy source biochar produced by slow pyrolysis is more effective in reducing greenhouse gas emissions when used as a soil conditioner.
  • Authors:
    • Weisskopf, P.
    • Leifeld, J.
    • Anken, T.
    • Hermle, S.
  • Source: Soil & Tillage Research
  • Volume: 98
  • Issue: 1
  • Year: 2008
  • Summary: Soil tillage and its interaction with climate change are widely discussed as a measure fostering carbon sequestration. To determine possible carbon sinks in agriculture, it is necessary to study carbon sequestration potentials in relation to agricultural management. The aim of this paper is to evaluate the soil carbon sequestration potential of a site in north-eastern Switzerland under different tillage systems. The study was performed as a long-term (19-year) trial on an Orthic Luvisol (sandy loam) with a mean annual air temperature of 8.4 °C and a long-term precipitation mean of 1183 mm. The soil organic carbon (SOC) concentration was determined five times during the study period, with the paper focussing mainly on the year 2006. The main objective was to quantify the influence of mouldboard ploughing (PL), shallow tillage (ST), no-tillage (NT) practices, and grassland (GL) on soil organic carbon content, the latter's different fractions (labile, intermediate, and stable), and its distribution by depth. In calculating the SOC content of the whole soil profile, we included a correction factor accounting for variations in bulk density (equivalent soil mass). The total SOC stock at a depth of 0-40 cm was 65 Mg C ha-1, and although higher under GL, did not differ significantly between PL, ST, and NT. SOC concentrations per soil layer were significantly greater for NT and ST (0-10 cm) than for PL, which had greater SOC concentrations than NT and ST at 20-30 cm depth. Both SOC concentrations and stocks (0-20 cm) were largest under GL. In all treatments, most of the carbon was found in the intermediate carbon fraction. There was no significant difference in any of the three SOC fractions between NT and ST, although there was between ST and PL. A sharp decrease in C-concentrations was observed in the first 7 years after the transition from grassland to arable land, with a new equilibrium of the carbon concentration in the 0-40 cm layer being reached 12 years later, with no significant difference between the tillage treatments. Overall, the results indicate that effects of tillage on soil carbon are small in moist, cold-temperate soils, challenging conversion into no-till as a measure for sequestering C.
  • Authors:
    • Grant, C. A.
    • Li, X.
    • Burton, D. L.
  • Source: Canadian Journal of Soil Science
  • Volume: 88
  • Issue: 2
  • Year: 2008
  • Summary: Fertilizer nitrogen use is estimated to be a significant source of nitrous oxide (N2O) emissions in western Canada. These estimates are based primarily on modeled data, as there are relatively few studies that provide direct measures of the magnitude of N2O emissions and the influence of N source on N2O emissions. This study examined the influence of nitrogen source (urea, coated urea, urea with urease inhibitor, and anhydrous ammonia), time of application (spring, fall) and method of application (broadcast, banded) on nitrous oxide emissions on two Black Chemozemic soils located near Winnipeg and Brandon Manitoba. The results of this 3-yr study demonstrated consistently that the rate of fertilizer-induced N2O emissions under Manitoba conditions was lower than the emissions estimated using Intergovernmental Panel on Climate Change (IPCC) coefficients. The Winnipeg site tended to have higher overall NO emissions (1.7 kg N ha(-1)) and fertilizer-induced emissions (-0.8% of applied N) than did the Brandon site (0.5 kg N ha(-1)), representing similar to 0.2% of applied N. N2O emissions in the first year of the study were much higher than in subsequent years. Both the site and year effects likely reflected differences in annual precipitation. The N2O emissions associated with the use of anhydrous ammonia as a fertilizer source were no greater than emissions with urea. Fall application of nitrogen fertilizer tended to result in marginally greater N2O emissions than did spring application, but these differences were neither large nor consistent.