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 community for glucose in soils from longterm experimental grassland plots, The plots had been treated annually with either farmyard manure, inorganic NPK fertilizers, farmyard manure+inorganic NPK fertilizers, (NH4)(2)SO4 only, or no experimental amendment since 1897. The largest biomass 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 biomass (qCO(2)) and high overall affinity for glucose (low K-m). The effects of the manure treatment were a greater biomass C and a lower overall glucose affinity than in the control plot. In the presence farmyard 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 greater glucose affinity but had no significant effect on the biomass, the biomass C to organic C ratio or qCO(2).