THE SPATIAL-DISTRIBUTION OF SOIL MICROBIAL BIOMASS IN A PERMANENT ROWCROP

The effects of soil texture (silt loam or sandy loam) and cultivation practice (green manure) on the size and spatial distribution of the mi crobial biomass and its metabolic quotient were investigated in soils planted with a permanent row crop of hops (Humulus lupulus). The soil both between and in the plant rows was sampled at three different dept hs (0-10, 10-20, and 20-30 cm). The silt loam had a higher overall mic robial biomass C concentration (260 mug g-1) than the sandy loam (185 mug g-1), whereas the sandy loam had a higher (3.1 mug CO2-C mg-1 micr obial C h-1) metabolic quotient than the silt loam (2.6 mug CO2-C mg-1 microbial C h-1), on average over depth (0-30 cm) and over all treatm ents. There was a sharp decrease in the microbial biomass with increas ing depth for all plots. However, this was more pronounced in the silt loam than in the sandy loam. There was no distinct influence of sampl ing depth on the metabolic quotient. The microbial biomass was conside rably higher in the rows than between the rows, especially in the silt loam plots. There was no significant difference between plots without green manure and plots with green manure for either the microbial bio mass or the metabolic quotient.