NITROUS-OXIDE EMISSIONS FROM SOILS DUE TO INPUTS OF NITROGEN FROM EXCRETA RETURN BY LIVESTOCK ON GRAZED GRASSLAND IN THE UK

Nitrous oxide (N2O) emissions from different soils under grass were me asured after treatment with cow dung and urine in field trials conduct ed during two separate seasons and in laboratory incubation experiment s. N2O emission rates were much higher during autumn-winter than durin g spring-summer, and in the case of well-drained soil were substantial for both excreta types (207 mg N2O-N kg(-1) of deposited dung and 197 mg N2O-N kg(-1) of urine in autumn-winter). The corresponding data fo r poorly-drained soil were 0.2 mg (dung) and 148 mg (urine). Emissions continued over much longer periods (similar to 60 days) from sandy an d stony loams than from a silty clay loam (similar to 30 days) under b oth field and laboratory conditions, and were not solely dependent on soil NO3- or NH4+ status but also related to other factors including s oil moisture, rate of plant growth and carbon availability. Results su ggest that N2O production occurred during both nitrification and denit rification processes. Emission rates of up to similar to 1590 mu g N2O -N h(-1) m(-2) occurred in the field, while small rates of deposition to the soil were occasionally observed. Under laboratory conditions, s imilar treatments produced large emissions from loam soils having pH o f 4.5-6.5 and zero emissions from a peat soil with pH of 3.8. The rati o of nitrogen released as N2O to the amount of N excreted by the lives tock varied from similar to 0% (summer) to 0.8-2.3% (winter), consiste nt with loss rates observed for mineral fertilizers. Copyright (C) 199 6 Elsevier Science Ltd