111. A simulation-based analysis of productivity and soil carbon in response to time-controlled rotational grazing in the West African Sahel region

• Authors:
  • Keita, M.
  • Kodio, A.
  • Nelson, R.
  • Jones, J. W.
  • Stöckle, C. O.
  • Badini, O.
• Source: Agricultural Systems
• Volume: 94
• Issue: 1
• Year: 2007
• Summary: In the Sahel region of West Africa, the traditional organization of the population and the grazing land avoided overexploitation of pastures. Since independence in the 1960s, grazing lands have been opened to all without specific guidance, and the vulnerability of the pastures to degradation has increased. Rotational grazing is postulated as a possible solution to provide higher pasture productivity, higher animal loads per unit land, and perhaps improved soil carbon storage. The objective of this study was to conduct a simulation-based assessment of the impact of rotational grazing management on pasture biomass production, grazing efficiency, animal grazing requirement satisfaction, and soil carbon storage in the Madiama Commune, Mali. The results showed that grazing intensity is the primary factor influencing the productivity of annual pastures and their capacity to provide for animal grazing requirements. Rotating the animals in paddocks is a positive practice for pasture protection that showed advantage as the grazing pressure increased. Increasing the size of the reserve biomass not available for grazing, which triggers the decision of taking the animals off the field, provided better pasture protection but reduced animal grazing requirements satisfaction. In terms of soil carbon storage, all management scenarios led to reduction of soil carbon at the end of the 50-year simulation periods, ranging between 4% and 5% of the initial storage. The differences in reduction as a function of grazing intensity were of no practical significance in these soils with very low organic matter content, mostly resistant to decomposition.

112. Transformation of nitrogen and nitrous oxide emission from grassland soils as affected by compaction

• Authors:
  • Hedley, M. J.
  • Bolan, N. S.
  • Saggar, S.
  • Bhandral, R.
• Source: Soil & Tillage Research
• Volume: 94
• Issue: 2
• Year: 2007
• Summary: Animal trampling is one of the main factors responsible for soil compaction under grazed pastures. Soil compaction is known to change the physical properties of the soil thereby affecting the transformation of nitrogen (N) and the subsequent of release of N as nitrous oxide (N2O). The form of N source added to these compacted soils further affects N emissions. Here we determine the interactive effects of soil compaction and form of N sources (cattle urine and ammonium, nitrate and urea fertilizers) on the loss of N through N2O emission from grassland soil. Overall, soil compaction caused a seven-fold increase in the N2O flux, the total N2O fluxes for the entire experimental period ranged from 2.62 to 61.74 kg N2O-N ha-1 for the compacted soil and 1.12 to 4.37 kg N2O-N ha-1 for the uncompacted soil. Among the N sources, the highest emissions were measured with nitrate application, emissions being 10 times more than those from other N sources for compacted soil, suggesting that the choice of N fertilizer can go a long way in mitigating N2O emissions in compacted grasslands.

113. Rotational grazing effects on rangeland vegetation at a farm scale

• Authors:
  • Deregibus, V. A.
  • Bartoloni, N.
  • Rodriguez, A. M.
  • Jacobo, E. J.
• Source: Rangeland Ecology & Management
• Volume: 59
• Issue: 3
• Year: 2006
• Summary: We evaluated the adequacy of rotational grazing to improve rangeland condition in the Flooding Pampa region, eastern Argentina, comparing the floristic composition dynamic of the 2 main plant communities under rotational and continuous grazing over a study period of 4 years (1993-1996). The experiment was conducted in commercial farms located in 4 sites of the Flooding Pampa region. In each site, a couple of farms, one managed under rotational grazing (implemented in 1989) and an adjacent one managed under continuous grazing at a similar stocking rate (1 AU(.)ha(-1)), constituted the replications of the experiment. Basal cover of species, litter, and bare soil were monitored in midslope and lowland grassland communities on each farm. Total plant basal cover in midslope and in lowland communities remained unchanged over the whole experimental period under both grazing methods. Under rotational grazing, litter cover was higher in both communities while the amount of bare soil showed a significant reduction in lowlands and a tendency to be lower in midslope. Basal cover of legumes, C-3 annual and C-3 perennial grasses was higher, while cover of C-4 prostrate grasses was lower under rotational grazing in the midslope community. In the lowland community, rotational grazing effects were evident only in the drier years, when higher cover of hydrophytic grasses and legumes and lower cover of forbs occurred. Plant species diversity did not change in response to grazing. In conclusion, rotational grazing promoted functional groups composed of high forage value species and reduced bare soil through the accumulation of litter. These changes indicate an improvement in rangeland condition and in carrying capacity. As the stocking rate was approximately 60% higher than the average stocking rate of the Flooding Pampa region, we believe that productivity and sustainability may be compatible by replacing continuous with rotational grazing.

114. Methane and nitrous oxide emissions from Canadian animal agriculture: A review

• Authors:
  • France, J.
  • Wagner-Riddle, C.
  • Clark, K.
  • Kebreab, E.
• Source: Canadian Journal of Animal Science
• Volume: 86
• Issue: 2
• Year: 2006
• Summary: Considerable evidence of climate change associated with emissions of greenhouse gases (GHG) has resulted in international efforts to reduce GHG emissions. The agriculture sector contributes about 8% of GHG emissions in Canada mostly through methane (CH4) and nitrous oxide (N2O). The objective of this paper was to compile an integrative review of CH4 and N2O emissions from livestock by taking a whole cycle approach from enteric fermentation to manure treatment and storage, and field application of manure. Basic microbial processes that result in CH4 production in the rumen and hindgut of animals were reviewed. An overview of CH4 and N2O production processes in manure, and controlling factors are presented. Most of the studies conducted in relation to enteric fermentation were in dairy and beef cattle. To date, research has focussed on GHG emissions from the stored manures of dairy, beef cattle and swine; therefore, we focus our review on these. Several methods used to measure GHG emissions from livestock and stored manure were reviewed. A comparison of methods showed that there were agreements between most of the techniques but some systematic differences were also observed. Additional studies with comprehensive comparisons of methodologies are needed in order to allow for comparison of results obtained from studies using contrasting methodologies. The need to standardize measurement methods and reporting to facilitate comparison of results and data integration was identified. Prediction equations are often used to calculate GHG emissions. Various types of mathematical approaches, such as statistical models, mechanistic models and estimates calculated from emission factors, and studies that compare various types of models are discussed herein. A lack of process-based models describing GHG emissions from manure during storage was identified. A brief description of mitigation strategies focussing on recent studies is given. Reduction in CH4 emissions from ruminants through the addition of fats in diets and the use of more starch was achieved and a transient beneficial effect of ionophores was reported. Grazing management and genetic selection also hold promise. Studies focussed on manure treatment options that have been suggested to reduce gas fluxes from manure storage, composting, anaerobic digestion (AD), diet manipulation, covers and solid-liquid separation, were reviewed. While some of these options have been shown to decrease GHG emissions from stored manure, different studies have obtained conflicting results, and additional research is needed to identify the most promising options. GHG emissions from pasture and croplands after manure application have been the subject of several experimental and modelling studies, but few of these have linked field emissions to diet manipulation or manure treatments. Further work focussing on the entire cycle of GHG formation from feed formulation, animal metabolism, excreta treatment and storage, to field application of manure needs to be conducted.

115. Management effects on soil CO2 efflux in northern semiarid grassland and cropland

• Authors:
  • Tanaka, D. L.
  • Liebig, M. A.
  • Frank, A. B.
• Source: Soil & Tillage Research
• Volume: 89
• Issue: 1
• Year: 2006
• Summary: Soil respiration is a process influenced by land use, management practices, and environmental conditions. Our objectives were to evaluate relationships between management-induced differences in soil organic carbon (SOC) and soil CO2 efflux from continuous no-till spring wheat (Triticum aestivum L.), spring wheat-fallow under no-till, and a native mixed-grass prairie with grazing near Mandan, ND. A Werner-Sen-Chama soil complex (Entic Haplustoll, Typic Haplustoll, and Typic Calciustoll) was present at the grassland site and a Wilton silt loam (Pachic Haplustoll) at the cropping sites. Soil chambers were used to measure soil CO2 effluxes about every 21 days starting 14 May 2001 to 1 April 2003. Soil water and soil temperature were measured at time of CO2 efflux measurements. Soil organic carbon, microbial biomass carbon (MBC), and above and belowground plant biomass were measured in mid-July each year. Root biomass to 0.3 m depth of the undisturbed grassland was significantly greater (12.3 Mg ha-1) than under continuous wheat (1.3 Mg ha-1) and wheat-fallow (0.3 Mg ha-1). Grassland SOC content of 84 Mg ha-1 to 0.3 m soil depth was 1.2 times greater than continuous wheat and 1.3 times greater than wheat-fallow. The MBC of the grassland was 2.2 Mg ha-1, or 3.6 times greater than continuous wheat and 7.2 times greater than wheat-fallow treatments. Soil CO2 efflux averaged 2.8 g CO2-C m-2 day-1 for grassland, compared to 1.9 g CO2-C m-2 day-1 for wheat fallow and 1.6 g CO2-C m-2 day-1 for continuous wheat treatments. Although these CO2 efflux rates were based on measurements made at intervals of about 21 days, the differences among treatments with time were rather consistent. Differences in soil CO2 efflux among treatments could be attributed to differences in SOC and MBC, suggesting that land use plays a significant role in soil CO2 efflux from respiration.

116. Forage supply systems for dryland dairy farms in southern Australia.

• Authors:
  • Kenny, S. N.
  • O'Brien, G. B.
  • Ward, G. N.
  • Jacobs, J. L.
  • Chapman, D. F.
  • Beca, D.
  • McKenzie, F. R.
• Source: Proceedings of the New Zealand Grassland Association
• Volume: 68
• Year: 2006
• Summary: Continued improvements in home grown forage consumption are needed to support the long-term profitability of the dairy industry in southern Australia. Most home grown forage currently comes from perennial ryegrass pastures, which have significant limitations in the southern Australia environment. These limitations threaten future productivity gains, and we therefore consider opportunities for using other plant species. Data on the production of alternative perennial grasses, brassica summer crops, C4 summer crops and winter cereals grown for whole-crop silage are limited and generally show large variation in yields between sites and years. Simulation models suggest that, once the base ryegrass pasture is well-utilised, incorporating complementary forages can return $70-$100/ha extra operating profit for every additional tonne of home grown forage DM consumed per ha. Double cropping (winter cereal or annual ryegrass followed by a summer crop of turnips or maize) and summer-active pastures such as tall fescue show particular promise. Further information is required on how to integrate these forages into whole farm feeding systems to realise the additional profit with manageable business and environmental risk.

117. Nitrous oxide emissions from Australian agricultural soils: a perspective on pastures and grain

• Authors:
  • Leuning, R.
  • Baigent, R.
  • Eckard, R.
  • Barker-Reid, F.
  • Phillips, F.
  • Gates, W.
  • Kelly, K.
  • Galbally, I. E.
  • Meyer, C. P.
  • Weeks, I. A.
• Source: Greenhouse 2005: action on climate change
• Year: 2005

118. Spatial variability of N2O emissions and contributing soil factors from an Australian irrigated dairy pasture

• Authors:
  • R,Leuning
  • IE,Galbally
  • K,Kelly
  • R,Edis
  • Y,Li
  • D,Turner
  • D,Chen
• Source: 4th International Symposium on non-CO2 Greenhouse Gases
• Year: 2005

119. Ethanol production using corn, switchgrass, and wood; biodiesel production using soybean and sunflower

• Authors:
  • Patzek, T. W.
  • Pimentel, D.
• Source: Natural Resources Research
• Volume: 14
• Issue: 1
• Year: 2005
• Summary: Energy outputs from ethanol produced using corn, switchgrass, and wood biomass were each less than the respective fossil energy inputs. The same was true for producing biodiesel using soybeans and sunflower, however, the energy cost for producing soybean biodiesel was only slightly negative compared with ethanol production. Findings in terms of energy outputs compared with the energy inputs were: * Ethanol production using corn grain required 29% more fossil energy than the ethanol fuel produced. * Ethanol production using switchgrass required 50% more fossil energy than the ethanol fuel produced. * Ethanol production using wood biomass required 57% more fossil energy than the ethanol fuel produced. * Biodiesel production using soybean required 27% more fossil energy than the biodiesel fuel produced (Note, the energy yield from soy oil per hectare is far lower than the ethanol yield from corn). * Biodiesel production using sunflower required 118% more fossil energy than the biodiesel fuel produced.

120. Management of Canadian prairie region grazed grasslands: Soil C sequestration, livestock productivity and profitability

• Authors:
  • Martin, R. C.
  • Patterson, G.
  • Fredeen, A.
  • Cohen, R. D. H.
  • Lynch, D. H.
• Source: Canadian Journal of Soil Science
• Volume: 85
• Issue: 2
• Year: 2005
• Summary: The GrassGro model (a computer simulation of management-induced changes in range and pasture forage and livestock productivity) was combined with spreadsheet analyses to estimate the influence of improved grazing practices on soil organic carbon (SOC), and farm profitability, across native rangelands and tame pastures of the southern Canadian Prairies. Improved practices included complementary grazing (CG) and reduced stocking density (RSD) on rangeland; and N fertilization (FERT), seeded grass/legumes grazed continuously (GLGC) or rotationally (GLGR), and RSD on tame pastures. The analysis was stratified into three ecoregions on the basis of similarities in climate and soil type. Averaged over 30 yr and ecoregions, SOC rates of gain through improved management were 5 (RSD) to 26 (CG) kg C ha(-1) yr(-1) for rangelands, and 86 (RSD), 75 (GLGC), 62 (GLGR) and 222 (FERT) kg C ha(-1) yr(-1) for tame pastures. Gains with FERT were considered largely negated by associated energy (C) costs, N2O emissions, and shifts in grassland species. The CG system alone improved net returns to the producer. The estimated potential combined SOC gain on prairie grazinglands (11.5 Mha) was 1.63 MMT CO2 yr(-1) (or 0.465 MMT C yr(-1)), slightly less than the 1.70 MMT CO2 yr(-1) currently emitted from agricultural soils in Canada.