Comparison of methodologies for field measurement of net nitrogen mineralisation in arable soils

This study evaluated the suitability of a soil core incubation technique (with acetylene added to inhibit loss of N by denitrification; CIT) and a resin-core incubation technique (RCT) for measurement of net N mineralisation under arable cropping conditions. A conventional N balance (BAL) approach to the measurement of N mineralisation was used for comparison. In a sandy soil during winter 1996/97, CIT estimates of net N mineralisation were approximately 3 times greater than RCT and BAL estimates, which were in close agreement. Soil disturbance (with the consequent exposure of physically protected organic matter) did not enhance the rate of net N mineralisation measured by CIT on the sandy, low-organic-matter soil studied, although an increase in soil aeration may have enhanced rates above those measured by RCT and BAL. Overall, RCT was considered to be the more favourable technique for estimation of net N mineralisation. It also provided a measure of nitrate leaching which was comparable to that obtained by porous ceramic water samplers. However, separate estimates of the likely loss of N by denitrification should be obtained with soils which are particularly vulnerable (eg. poor aeration and high clay or water content). Spatial variability was a particular problem with all three techniques which can be overcome by taking a large number of soil cores to increase sample replication.