Fate of nitrogen in pig effluent applied to a shallow stony pasture soil

Abstract

A 2‐year lysimeter experiment was conducted to determine the fate of nitrogen (N) in pig effluent applied to a shallow stony pasture soil. In the first year (1991), pig effluent was applied in a single application at three rates of total N (0, 200, and 600 kg N/ha) to 12 monolith lysimeters (500 mm diameter × 450 mm deep) during autumn (March). In the second year of the experiment, the 200 kg N/ha lysimeters received a repeat application using ¹⁵N‐labelled effluent. Application at the 200 kg N/ha rate resulted in: 10% of the applied N being lost by ammonia volatilisation; 5% being leached (11 kg N/ha) in the first year and less than 2.5% of applied ¹⁵N being leached in the second year; 35% of the applied effluent ¹⁵N was recovered by the pasture; and 14% was recovered in the soil plus roots. Denitrification losses (estimated by difference) were high (39%) and were attributed to the soluble carbon content of the effluent, a supply of nitrate from nitrification of slurry N, and transient anaerobic conditions which probably occurred at the soil/gravel interface. Application at the 600 kg N/ha rate resulted in a large leaching loss (116 kg N/ha) and a high concentration of NO3‐N in the drainage water. Application of effluent at either rate resulted in a considerable increase in pasture production, and this was attributed to improved plant nutrition.