INVESTIGATIONS ON DENITRIFICATION POTENTIAL IN AGRICULTURAL SOILS AS RELATED WITH AFFECTED FACTORS

Denitrification potential（DP） of agricultural soils as related．with affected factors was studied in incubation，Results indicated．in soil profile of upland fluvo－aquic soil DP was the highest（49％）in top soil（0～20cm）in incubation day 20 and was very low below the layer to 100cm．except for the horizon of 52～65cm．Addition of glucose promoted DP in all soil horizons， especialy during the early period of the incubation．The increase in DP in all other horiozons were higher than that in top soil，although the value of DP in top soil was still the highest．Addition of clear solution of fertile soil also increased the denitrification of all soil layers，but with less extent than that with addition of glucose．Addition of phosphorus had no effect on DP of all soil layers． The highest of DP was also observed in the top soil of the paddy soil with moderate fertility and the value was 74％ in 20－d incubation．DP decreased gradually as the depth of the soil profile． Addition of glucose or clear solution of fertile soil had no effect on DP in both 0～20cm and 20～40cm layers．but enhanced DP obivously in the layers from 40～100cm．No effect of addtion of phosphrous on DP was not obeserved in all soil layers. The values of DP in all soil layers of upland red soil profile collected from peanut field were very low，only 18％ in top soil and near zero in the layers below surface soil in 20－d incubation，Addition of glucose or clear solution of fertile soil increased DP in top layer of 0～20om in 20－d incubation，but had no effect on the layers below the top．No effect of addition phosphorus on DP of the red soil profile were observed． It was found that there is a significant correlation of DP with the content of soil organic matter for all the soils studied． the correlation coefflclentwas 0．827**． However，no such correlation Was found for DP with the content of soil available phosphrus and soil pH．