NITROGEN TRANSFORMATIONS IN A PEATY SOIL IMPROVED FOR PASTORAL AGRICULTURE

Microbial transformations and chemical distribution of N were compared in two upland stagnohumic gley soils at the same site. In 1981 one so il was improved for more intensive agriculture by lime and fertilizer applications and reseeding with a grass/clover mixture. The other soil (referred to here as unimproved) was also reseeded in 1981, but no li me was added and the sward has subsequently reverted to rough grazing land. Improvement resulted in greater soil microbial activity. The imp roved soil showed greater rates of denitrification, net N immobilizati on and N fixation (acetylene reduction) and contained more microbial b iomass N than the unimproved soil. However, no major differences in th e distribution of organic N fractions were detected. This indicates th at a large amount of the soil N present before improvement did not und ergo mineralization and remained unavailable to plants.