Monday, November 13, 2006

Effect of Soil Compaction on Nitrogen Volatilization in a Management Intensive Grazing System.

R. L. Miller, Utah State Univ, 2300 Old Main Hill, Logan, UT 84322-2300 and L. A. Petersen, Utah State University, 2300 Old Main Hill, Logan, UT 84322-2300.

Management Intensive Grazing (MIG), a rotational grazing program, utilizes high animal stocking rates to efficiently harvest pasture crops. Unfortunately, MIG produces high concentrations of livestock excreta which increases environmental concerns about nitrogen leaching and volatilization. Little research has been performed on heavy textured soils with high pH which are typical of the Intermountain West. A laboratory experiment was conducted to provide base-line data on total N losses resulting from animal urine deposits in grazed pastures. A silt loam comprised of 17% clay, 28% sand, and 55% silt, and a loam soil, comprised of 22% clay, 28% sand, and 50% silt, were used. Soil cores were extracted at field capacity by pushing 14.8 cm diameter x 30.48 cm deep polyvinylchloride (PVC) pipes into the soil. Three compaction levels of 1.2, 1.3, 1.4 mg cm-3 were achieved by striking the soil surface with a metal plate until the desired volume was achieved. After three days, bovine urine harvested from lactating dairy cows was applied at a rate of 1000 lb N/acre, to represent the super-saturation of cattle urine pools under field conditions. Any leachate produced was collected and analyzed for total N content. Soil moisture was monitored every 2-3 days by weight and distilled water was added to restore soil cores to field capacity. Cores were incubated for 12 weeks in ambient laboratory conditions with day/night temperatures of 65-75° F. Upon completion of the incubation period, the PVC core containers were cut vertically and soil was removed, mixed, and a representative sample was analyzed for total N content. Differences between beginning soil nitrogen, N present in urine fertilizer, leachate losses, and ending soil nitrogen were examined, using a mass balance analysis. Volatilization losses were greater in soils with increased clay content and higher bulk density levels.