CONCURRENT MEASUREMENTS OF NET MINERALIZATION, NITRIFICATION, DENITRIFICATION AND LEACHING FROM FIELD INCUBATED SOIL CORES

An improved method is described for incubating intact soil cores in th e field, which permits concurrent measurement of net mineralization, n itrification, denitrification and leaching. Cores were enclosed in PVC tubes with minimal disturbance to the physical state or to the natura l cycles of wetting/drying, soil temperature and aeration during an in cubation lasting 4-5 days. An example of the application of the method is given in which soils with contrasting drainage characteristics wer e compared. Over a 64-day experimental period, 58% of the mineralized nitrogen (N) in a freely drained soil was nitrified and 36% of the nit rate-N (NO3--N) was denitrified. In a poorly drained soil, 72% of the mineralized N was nitrified and 63% of the NO3--N was denitrified. In both soil types, 18% of the remaining NO3--N was leached. Rates of nit rification were significantly correlated with net mineralization (r(2) = 0.41 and 0.52) and also closely correlated with denitrification (r( 2) = 0.67 and 0.68) in the freely and poorly drained soils, respective ly. Independent measurements of these processes, using alternative tec hniques (for the same period), compared favourably with measurements o btained with the improved incubation method. Adoption of this method h as a number of advantages with respect to field net N mineralization, and also allows interpretation of the impact this may have on other N transformation processes.