A SOIL CORE METHOD FOR ESTIMATING N-MINERALIZATION AND DENITRIFICATION DURING COVER CROP DECOMPOSITION

A soil core method is described for monitoring rates and extent of N-m ineralization and denitrification from intact leguminous cover crops ( e.g., hairy vetch) as a function of soil water content, The method als o allows for estimates of N-fixation in order to perform N-mass balanc es, Field conditions were simulated by growing cover crops in soil cor es from seed to biomass levels comparable to the field, followed by ha rvest/kill. Soil cores were wetted periodically using a rain simulator , After simulated rain events, samples of leachate were obtained and s oil water content adjusted by application of a vacuum (15 kPa) to the bottom of cores, The use of a PVC/silica filter (bubble point = 30 kPa ) allowed for cores to be drained to field capacity without pulling am bient air through the soil, N-fixation (before harvest/kill) and N-min eralization (after harvest/kill) were determined by comparing NO3- lea ched from vetch with fallow cores. Denitrification was determined by p eriodically sealing cores, injecting and recirculating acetylene throu ghout cores, and quantifying N2O production after 48 h. Preliminary ex periments with hairy vetch (Vicia villosa) indicate that plants are re asonably efficient at taking up soil NO;, intact roots decompose fairl y rapidly in soil (<6 weeks), and there is potential for substantial l osses of soil NO; as a result of denitrification at soil water content s greater than or equal to 70%.