O-2 UPTAKE, C METABOLISM AND DENITRIFICATION ASSOCIATED WITH MANURE HOT-SPOTS

O-2, C and N metabolism in organic hot-spots (sites where the intensit y of microbial respiration creates a high O-2 demand) was studied with fresh or anaerobically digested liquid cattle manure as substrates. A gel-stabilized mixture of soil and manure, 16 mm thick, was sandwiche d between layers of soil with a water content adjusted to field capaci ty, and incubated at 15 degrees C for up to 3 wk. When fresh manure wa s used, O-2 microprofiles demonstrated an O-2 penetration into the hot -spot of <1 mm after 1-3 d, increasing to ca. 2 mm after 3 wk. During this time, O-2 uptake rates decreased from 100-150 to ca. 50 nmol O-2 cm(-2) h(-1). With digested manure, the lower C availability in this s ubstrate resulted in Or penetration depths of 3-4 mm and O-2 uptake ra tes of <30 nmol O-2 cm(-2) h(-1) throughout the 3 wk. Maximum denitrif ication rates were also consistently lower with digested manure (4 nmo l N cm(-2) h(-1)) than with fresh manure (18 nmol N cm(-2) h(-1)). A n umerical model of NO3- transport indicated that denitrification was li mited by the availability of NO3- during the first week in the fresh m anure treatment, and that the soil was the only significant source of NO3- during at least 3 d; after this time nitrification at the soil-ma nure interface became increasingly important. After the first week wit h fresh manure, and throughout the experiment with digested manure, C availability apparently regulated denitrification.