INFILTRATION OF SLURRY LIQUID AND AMMONIA VOLATILIZATION FROM PIG AND CATTLE SLURRY APPLIED TO HARROWED AND STUBBLE SOILS

Abstract

A large amount of the ammonia present in the atmosphere has volatilized from animal slurries added to agricultural fields. This loss of ammonia (NH₃) causes both an unwanted decrease in fertilizer efficiency and an unwanted increase of nitrogen in oligotrophic waters. The effects of soil and slurry type on the infiltration of slurry liquid into soils, either pre-tilled with a harrow or in stubble, and how this in turn affects ammonia volatilization, were considered in this study. Experiments were performed on undisturbed soil cores (0.098 m diameter, 0.08 m length) of loamy sand and sandy loam. Either cattle or pig slurry, spiked with bromide as a tracer for water flow, was introduced to the columns, which initially were equilibrated to a soil water potential of −150 cm. NH₃ volatilization was measured by drawing air continuously across the soil surface and trapping ammonia. At 1, 4, 24, 48, 72 h after slurry application, soil columns were cut into slices and the concentrations of bromide, ammonium, and nitrate were determined at different depths.

The volatilization rate of ammonia was greatest during the early postapplication period. For the period 24–48 h after application, the rate of volatilization declined to an average of only 5% of the rate for the period 0–1 h after application. Volatilization of ammonia was generally higher from cattle slurry than from pig slurry. Harrowing resulted in reduced ammonia volatilization from pig slurry, which was most pronounced on the sandy loam soil. This effect decreased with time. For cattle slurry, harrowing had no significant effect on NH₃ volatilization. Seventy-two hours after slurry application, accumulative emissions of ammonia from slurry applied to harrowed soil were 2 to 16% lower than from slurry applied to stubble soil.