SIZE AND ACTIVITY OF SOIL MICROBIAL COMMUNITIES IN LONG-TERM EXPERIMENTAL GRASSLAND PLOTS TREATED WITH MANURE AND INORGANIC FERTILIZERS

We determined the size, activity, and affinity of the microbial commun ity for glucose in soils from longterm experimental grassland plots, T he plots had been treated annually with either farmyard manure, inorga nic NPK fertilizers, farmyard manure+inorganic NPK fertilizers, (NH4)( 2)SO4 only, or no experimental amendment since 1897. The largest bioma ss and activity differences were between the (NH4)(2)SO4-treatrd soil, which was very acid. and the rest, which were nearer neutral. In the (NH4)(2)SO4-treated soil, the biomass C to organic C ratio was small, but overall the community had high respiratory activity per unit of bi omass (qCO(2)) and high overall affinity for glucose (low K-m). The ef fects of the manure treatment were a greater biomass C and a lower ove rall glucose affinity than in the control plot. In the presence farmya rd manure, NPK led to smaller biomass and a lower biomass to organic C ratio while having no significant effect on either glucose K-m or qCO (2). In the absence of farmyard manure, NPK led to significantly great er glucose affinity but had no significant effect on the biomass, the biomass C to organic C ratio or qCO(2).