, Volume 127, Issue 2, pp 157-167

Microbial biomass and mineral N transformations in soil planted with barley, ryegrass, pea or turnip

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Plants of barley (Hordeum vulgare), ryegrass (Lolium perenne), pea (Pisum sativum) or turnip (Brassica campestris rapifera) were grown in pots of unfertilised soil for 10 weeks together with unplanted control pots. A wide range of soil microbiological parameters was measured on bulk soil samples 2, 4, 7 and 10 weeks after seedlings were transplanted. There was no effect of planting or differential effect of plant species upon respiration rate, microbial biomass N, or biomass of microbial predators, but these parameters all varied significantly over time. Respiration, biomass N and nematode biomass all increased, whilst protozoan biomass decreased. Microbial biomass C showed no significant temporal changes or effect of planting. There was evidence for differential plant effects on potential nitrification and denitrification. Nitrification rates were depressed, compared with the fallow, in all treatments except the pea, at some time in the experiment. Conversely denitrification rates were enhanced in all treatments, except the grass, at specific times. Denitrification rates were greater in the pea treatment than the fallow on all occasions. These results demonstrate that plants do not necessarily influence the gross microbiology of the soil, but may affect physiologically distinct sub-components of the microbial biomass.