NITRIFICATION AND DENITRIFICATION AFTER DIRECT INJECTION OF LIQUID CATTLE MANURE

Soil cores were collected in and around an injection slit in each of two field plots on a coarse sandy soil. The plots received either raw or anaerobically digested liquid cattle manure at a rate of 240 kg NH4+-N ha-1. During the three week period of the experiment, concentrations of dissolved organic carbon and NH4+ and the moisture content of cores from the injection slit were consistently above the background level in the soil. Denitrification activity was only registered in soil cores sampled in the injection slit. A dramatic increase occurred between Day 14 and Day 21, when the denitrification rate reached 3.5 kg N ha-1 day-1 in cores from the plot treated with raw manure, while the rate was 20-fold lower in the plot treated with digested manure. Nitrate accumulated between Day 7 and Day 21, suggesting a coupling between nitrification and denitrification.