Tuesday, November 14, 2006
187-6
Soil C and N Fractions in Cropping Systems Integrated with Livestock.
Alan Franzluebbers, USDA-ARS-NPA-SPNRU, USDA-ARS, 1420 Experiment Station Rd., Watkinsville, GA 30677
Integration of livestock in cropping systems of the southeastern USA could increase farm income diversity and improve nutrient cycling dynamics to increase resource efficiency. A long-term pasture was terminated and planted to cropping systems with and without cattle grazing of cover crops to determine production responses, as well as soil chemical, physical, and biological responses. Sorghum and corn with rye cover crop and winter wheat with pearl millet cover crop were managed with conventional and no tillage. Total, particulate, microbial biomass, and mineralizable C and N fractions were determined at depths of 0-3, 3-6, 6-12, and 12-20 cm on an annual basis during cropping. Tillage management had a large effect on the vertical distribution of soil C and N fractions in the soil, as expected. Whether cattle grazed cover crops or not resulted in relatively small changes in soil C and N fractions, although soil microbial biomass C did increase significantly near the soil surface with grazing compared to without grazing at the end of 3 years of cropping. Often, soil C and N fractions respond to management in a similar manner, but sometimes unique changes occur that can give us insight into how to improve nutrient cycling for increased resource efficiency.