Nitrous oxide release from soils receiving N-rich crop residues and paper mill sludge in eastern Scotland

Abstract

Incorporation of crop residues and other organic material to agricultural soils may increase nitrous oxide (N 2O) emissions, depending on the quantity and quality of the incorporated material. The effects of combining materials of contrasting quality on these emissions have still to be investigated. In this paper, the effects of applying paper mill sludge (PMS), incorporating plant residues, and cultivation on emissions of N 2O are reported. Two field experiments were undertaken on Cambisol soils (FAO classification), previously cropped to iceberg lettuce ( Lactuca sativa var. saladin) and calabrese ( Brassica oleracea italica var. cymosa) in Fife, eastern Scotland. Emissions were measured using both automated and manual closed chambers and comparisons were made between these techniques. Nitrous oxide emissions were high after incorporation of PMS; with up to 4.9 kg N 2ON ha −1 emitted over the first 3 weeks. These increased emissions were probably due to the high input of organic C for denitrification. Emissions from deep ploughed PMS treatments were higher ( P<0.05) than from rotary tilled and conventional ploughed treatments. Application of PMS resulted in an increase in microbial biomass C, but not biomass N. Measurements using autochambers recorded higher N 2O emissions than those obtained by less frequent manual measurements, partly due to diurnal variations in N 2O with soil temperature. High Q 10s (up to 4.0) for this temperature response were recorded in one period in July. It is recommended that diurnal temperature variations be recorded when sampling from manual closed flux chambers so that corrections can be made for diurnal variation in N 2O.