- Authors:
- White, R. E.
- Chapman, D. F.
- Eckard, R. J.
- Source: Australian Journal of Agricultural Research
- Volume: 58
- Issue: 12
- Year: 2007
- Authors:
- Apan, A.
- Maraseni, T. N.
- Cockfield, G.
- Source: Journal of Environmental Science and Health, Part A: Toxic/Hazardous Substances and Environmental Engineering
- Volume: 42
- Issue: 1
- Year: 2007
- Authors:
- McGregor, A.
- Slattery, B.
- Ugalde, D.
- Brungs, A.
- Kaebernick, M.
- Source: Soil & Tillage Research
- Volume: 97
- Issue: 2
- Year: 2007
- Authors:
- Barlow, E. W. R.
- Whetton, P. H.
- Webb, L. B.
- Source: Australian Journal of Grape and Wine Research
- Volume: 13
- Issue: 3
- Year: 2007
- Authors:
- North Carolina Department of Revenue
- Year: 2007
- Authors:
- Paustian, K.
- Williams, S.
- Easter, M.
- Breidt, F. J.
- Ogle, S. M.
- Source: Ecological Modelling
- Volume: 205
- Issue: 3-4
- Year: 2007
- Summary: Simulation modelling is used to estimate C sequestration associated with agricultural management for purposes of greenhouse gas mitigation. Models are not completely accurate or precise estimators of C pools, however, due to insufficient knowledge and imperfect conceptualizations about ecosystem processes, leading to uncertainty in the results. It can be difficult to quantify the uncertainty using traditional error propagation techniques, such as Monte Carlo Analyses, because of the structural complexity of simulation models. Empirically based methods provide an alternative to the error propagation techniques, and our objective was to apply this alternative approach. Specifically, we developed a linear mixed-effect model to quantify both bias and variance in modeled soil C stocks that were estimated using the Century ecosystem simulation model. The statistical analysis was based on measurements from 47 agricultural experiments. A significant relationship was found between model results and measurements although there were biases and imprecision in the modeled estimates. Century under-estimated soil C stocks for several management practices, including organic amendments, no-till adoption, and inclusion of hay or pasture in rotation with annual crops. Century also over-estimated the impact of N fertilization on soil C stocks. For lands set-aside from agricultural production, Century under-estimated soil C stocks on low carbon soils and over-estimated the stocks on high carbon soils. Using an empirically based approach allows for simulation model results to be adjusted for biases as well as quantify the variance associated with modeled estimates, according to the measured "reality" of management impacts from a network of experimental sites.
- Authors:
- Lachnicht-Weyers, S. L.
- Tillman, P. G.
- Whitehead, P. G.
- Singh, B. P.
- Schomberg, H. H.
- Sainju, U. M.
- Source: Soil & Tillage Research
- Volume: 96
- Year: 2007
- Summary: Cover crops may influence soil carbon (C) sequestration and microbial biomass and activities by providing additional residue C to soil. We examined the influence of legume [crimson clover (Trifolium incarnatum L.)], nonlegume [rye (Secale cereale L.)], blend [a mixture of legumes containing balansa clover (Trifolium michelianum Savi), hairy vetch (Vicia villosa Roth), and crimson clover], and rye + blendfmixture cover crops on soil C fractions at the 0-150 mm depth from 2001 to 2003. Active fractions of soil C included potential C mineralization (PCM) and microbial biomass C (MBC) and slow fraction as soil organic C (SOC). Experiments were conducted in Dothan sandy loam (fine-loamy, kaolinitic, thermic, Plinthic Kandiudults) under dryland cotton (Gossypium hirsutum L.) in central Georgia and in Tifton loamy sand (fine-loamy, siliceous, thermic, Plinthic Kandiudults) under irrigated cotton in southern Georgia, USA. Both dryland and irrigated cotton were planted in strip tillage system where planting rows were tilled, thereby leaving the areas between rows untilled. Total aboveground cover crop and cotton C in dryland and irrigated conditions were 0.72-2.90 Mg C ha-1 greater in rye + blend than in other cover crops in 2001 but was 1.15-2.24 Mg C ha-1 greater in rye than in blend and rye + blend in 2002. In dryland cotton, PCM at 50-150 mm was greater in June 2001 and 2002 than in January 2003 but MBC at 0-150 mm was greater in January 2003 than in June 2001. In irrigated cotton, SOC at 0-150 mm was greater with rye + blend than with crimson clover and at 0-50 mm was greater in March than in December 2002. The PCM at 0-50 and 0-150 mm was greater with blend and crimson clover than with rye in April 2001 and was greater with crimson clover than with rye and rye + blend in March 2002. The MBC at 0-50 mm was greater with rye than with blend and crimson clover in April 2001 and was greater with rye, blend, and rye + blend than with crimson clover in March 2002. As a result, PCM decreased by 21-24 g CO2-C ha-1 d-1 but MBC increased by 90-224 g CO2-C ha-1 d-1 from June 2001 to January 2003 in dryland cotton. In irrigated cotton, SOC decreased by 0.1-1.1 kg C ha-1 d-1, and PCM decreased by 10 g CO2-C ha-1 d-1 with rye to 79 g CO2-C ha-1 d-1 with blend, but MBC increased by 13 g CO2-C ha-1 d-1 with blend to 120 g CO2-C ha-1 d-1 with crimson clover from April 2001 to December 2002. Soil active C fractions varied between seasons due to differences in temperature, water content, and substrate availability in dryland cotton, regardless of cover crops. In irrigated cotton, increase in crop C input with legume + nonlegume treatment increased soil C storage and microbial biomass but lower C/N ratio of legume cover crops increased C mineralization and microbial activities in the spring.
- Authors:
- Valentini, R.
- Tubaf, Z.
- Sutton, M.
- Manca, G.
- Stefani, P.
- Skiba, U.
- Rees, R. M.
- Baronti, S.
- Raschi, A.
- Neftel, A.
- Nagy, Z.
- Martin, C.
- Kasper, G.
- Jones, M.
- Horvath, L.
- Hensen, A.
- Fuhrer, J.
- Flechard, C.
- Domingues, R.
- Czobel, S.
- Clifton-Brown, J.
- Ceschia, E.
- Campbell, C.
- Amman, C.
- Ambus, P.
- Pilegaard, K.
- Allard, V.
- Soussana, J. F.
- Source: Agriculture, Ecosystems & Environment
- Volume: 121
- Issue: 1-2
- Year: 2007
- Summary: The full greenhouse gas balance of nine contrasted grassland sites covering a major climatic gradient over Europe was measured during two complete years. The sites include a wide range of management regimes (rotational grazing, continuous grazing and mowing), the three main types of managed grasslands across Europe (sown, intensive permanent and semi-natural grassland) and contrasted nitrogen fertilizer supplies. At all sites, the net ecosystem exchange (NEE) of CO2 was assessed using the eddy covariance technique. N2O emissions were monitored using various techniques (GC-cuvette systems, automated chambers and tunable diode laser) and CH4 emissions resulting from enteric fermentation of the grazing cattle were measured in situ at four sites using the SF6 tracer method. Averaged over the two measurement years, net ecosystem exchange (NEE) results show that the nine grassland plots displayed a net sink for atmospheric CO2 of -240 +/- 70 g C m(-2) year(-1) (mean confidence interval at p > 0.95). Because of organic C exports (from cut and removed herbage) being usually greater than C imports (from manure spreading), the average C storage (net biome productivity, NBP) in the grassland plots was estimated at -104 +/- 73 g cm(-2) year(-1) that is 43% of the atmospheric CO2 sink. On average of the 2 years, the grassland plots displayed annual N2O and CH4 (from enteric fermentation by grazing cattle) emissions, in CO2-C equivalents, of 14 +/- 4.7 and 32 +/- 6.8 g CO2-C equiv. m(-2) year(-1), respectively. Hence, when expressed in CO2-C equivalents, emissions of N2O and CH4 resulted in a 19% offset of the NEE sink activity. An attributed GHG balance has been calculated by subtracting from the NBP: (i) N2O and CH4 emissions occurring within the grassland plot and (ii) off-site emissions of CO2 and CH4 as a result of the digestion and enteric fermentation by cattle of the cut herbage. On average of the nine sites, the attributed GHG balance was not significantly different from zero (-85 +/- 77 g CO2-C equiv. m(-2) year(-1)).
- Authors:
- Mangum, R. W.
- Coffman, C. B.
- Teasdale, J. R.
- Source: Agronomy Journal
- Volume: 99
- Issue: 5
- Year: 2007
- Summary: There have been few comparisons of the performance of no-tillage cropping systems vs. organic farming systems, particularly on erodible, droughty soils where reduced-tillage systems are recommended. In particular, there is skepticism whether organic farming can improve soils as well as conventional no-tillage systems because of the requirement for tillage associated with many organic farming operations. A 9-yr comparison of selected minimum-tillage strategies for grain production of corn (Zea mays L.), soybean [Glycine max (L.) Merr.], and wheat (Triticum aestivum L.) was conducted on a sloping, droughty site in Beltsville, MD, from 1994 to 2002. Four systems were compared: (i) a standard mid-Atlantic no-tillage system (NT) with recommended herbicide and N inputs, (ii) a cover crop-based no-tillage system (CC) including hairy vetch (Vicia villosa Roth) before corn, and rye (Secale cereale L.) before soybean, with reduced herbicide and N inputs, (iii) a no-tillage crownvetch (Coronilla varia L.) living mulch system (CV) with recommended herbicide and N inputs, and (iv) a chisel-plow based organic system (OR) with cover crops and manure for nutrients and postplanting cultivation for weed control. After 9 yr, competition with corn by weeds in OR and by the crownvetch living mulch in CV was unacceptable, particularly in dry years. On average, corn yields were 28 and 12% lower in OR and CV, respectively, than in the standard NT, whereas corn yields in CC and NT were similar. Despite the use of tillage, soil combustible C and N concentrations were higher at all depth intervals to 30 cm in OR compared with that in all other systems. A uniformity trial was conducted from 2003 to 2005 with corn grown according to the NT system on all plots. Yield of corn grown on plots with a 9-yr history of OR and CV were 18 and 19% higher, respectively, than those with a history of NT whereas there was no difference between corn yield of plots with a history of NT and CC. Three tests of N availability (corn yield loss in subplots with no N applied in 2003-2005, presidedress soil nitrate test, and corn ear leaf N) all confirmed that there was more N available to corn in OR and CV than in NT. These results suggest that OR can provide greater long-term soil benefits than conventional NT, despite the use of tillage in OR. However, these benefits may not be realized because of difficulty controlling weeds in OR.
- Authors:
- Source: Environmental Research Letters
- Volume: 2
- Issue: 1
- Year: 2007
- Summary: Changes in the global production of major crops are important drivers of food prices, food security and land use decisions. Average global yields for these commodities are determined by the performance of crops in millions of fields distributed across a range of management, soil and climate regimes. Despite the complexity of global food supply, here we show that simple measures of growing season temperatures and precipitation - spatial averages based on the locations of each crop - explain similar to 30% or more of year-to-year variations in global average yields for the world's six most widely grown crops. For wheat, maize and barley, there is a clearly negative response of global yields to increased temperatures. Based on these sensitivities and observed climate trends, we estimate that warming since 1981 has resulted in annual combined losses of these three crops representing roughly 40 Mt or $5 billion per year, as of 2002. While these impacts are small relative to the technological yield gains over the same period, the results demonstrate already occurring negative impacts of climate trends on crop yields at the global scale.
