Monday, August 4, 2008
Exhibit Hall CD, Midwest Airlines Center
Background/Question/Methods Cattle ranching are one of the most significant factors that contribute to the elevated rates of forest deforestation and soil erosion, producing further effects in global biogeochemistry. Thus, ecological restoration is often associated with the exclusion of livestock, especially in the tropics. It may improve the quantity and quality of plant biomass, soil organic matter and nutrients, and recovery physical properties of the soils, which assist the establishment and development of vegetation of the perturbed areas. The land-cover change reduces the aboveground biomass and reincorporation of organic matter to soil. Livestock also changes soil density, which furthermore affects the stability of soil aggregates, water infiltration capacity, and conservation of soil nutrients. In contrast, the presence of cattle raises the amount of nitrogen (N) available for plants, reduces the carbon:nitrogen (C:N) ratio of soil organic matter and improves its mineralization. Which are the short time effects in physical and biogeochemical soil properties of cattle exclusion in an experimental grid in active pasture adjacent to tropical rain forest in Veracruz, Mexico? We evaluated soil texture, density, pH, organic C, total and mineral N of soil samples at 0-0.05 m and 0.05-0.2 m depth in October 2006 and three month after cattle exclusion. Project design consisted of 24 fenced plots (30x30 m) and 8 active pasture plots.
Results/Conclusions The results indicate that the sandy-loam soils were acidic, rich in organic matter, the ratio C:N was 10 and the relation nitrate:ammonium was 2. As expected, the concentrations of organic C, total and inorganic N were greatest in the upper soil (0-0.5 m depth). The exclusion of cattle did not affect the concentration of soil C, but in contrast, showed lower soil pH relative to active pasture. The concentrations of total and mineral N were greater in active pasture plots than plots without livestock. Thus, the ratio C:N decreased in soils of active pasture. Finally, nitrate:ammonium ratio increased from two in open pasture soils to three in close pasture soils. In conclusion, and despite of the short time of the exclusion of cattle, we found a difference in soil pH, but not in soil density and soil organic matter. Even though, the changes in soil properties could improve the availability of N because of the favoring conditions for microbial activity.
Results/Conclusions The results indicate that the sandy-loam soils were acidic, rich in organic matter, the ratio C:N was 10 and the relation nitrate:ammonium was 2. As expected, the concentrations of organic C, total and inorganic N were greatest in the upper soil (0-0.5 m depth). The exclusion of cattle did not affect the concentration of soil C, but in contrast, showed lower soil pH relative to active pasture. The concentrations of total and mineral N were greater in active pasture plots than plots without livestock. Thus, the ratio C:N decreased in soils of active pasture. Finally, nitrate:ammonium ratio increased from two in open pasture soils to three in close pasture soils. In conclusion, and despite of the short time of the exclusion of cattle, we found a difference in soil pH, but not in soil density and soil organic matter. Even though, the changes in soil properties could improve the availability of N because of the favoring conditions for microbial activity.
