Showing papers by "Richard D. Bardgett published in 1995"

Soil microbial biomass and activity in long-term grassland : effects of management changes

Abstract: The effects of long-term N fertilizer management history and field drainage on soil microbial biomass N and C and its activity in the surface soil of a poorly-drained pasture soil in S.W. England were examined periodically for 1 year. The immediate effects of changes in N fertilizer inputs were also determined. In general, there were few differences in the trends of biomass C and N with time, nor of drainage, withdrawal of fertilizer N from a previously-fertilized soil, or addition of fertilizer N to a previously-unfertilized soil. However, soil microbial biomass N and C were substantially greater in the previously-unfertilized than in the fertilized treatment. Measurements of ATP, enzyme activity and respiration made on one occasion indicated, in contrast to the microbial biomass status, significant effects of both the short- and long-term treatments. There was also a substantial difference in the numbers of culturable bacteria with over 4 times less being present in soils without previous N application, again in contrast to total biomass contents: cfu of fungi were not influenced by any of the treatments. Important differences in microbial activity in response to short-term management changes were therefore demonstrated which may have an effect on N cycling in grassland soils. There is a need to understand the factors controlling these soil microbial characteristics and to identify and quantify differences in microbial community structure, in order to make greater progress in increasing the efficiency of N utilization.

The short-term effects of cessation of fertiliser applications, liming, and grazing on microbial biomass and activity in a reseeded upland grassland soil

Abstract: A field study was conducted to determine the influence of a short-term (2 year) cessation of fertiliser applications, liming, and sheep-grazing on microbial biomass and activity in a reseeded upland grassland soil. The cessation of fertiliser applications (N and NPK) on a limed and grazed grassland had no effect on microbial biomass measurements, enzyme activities, or respiration. Withholding fertiliser and lime from a grazed grassland resulted in significant reductions in both microbial biomass C (P<0.05) and dehydrogenase activity (P<0.05) by approximately 18 and 21%, respectively. The removal of fertiliser applications, liming, and grazing resulted in even greater reductions in microbial biomass C (44%, P<0.001) and dehydrogenase activity (31%, P<0.001), and significant reductions in microbial biomass N (P<0.005), urease activity (P<0.05), phosphatase activity (P<0.001), and basal respiration (P<0.05). The abundance of culturable bacteria and fungi and the soil ATP content were unaffected by changes in grassland managements. With the cessation of liming soil pH fell from 5.4 to 4.7, and the removal of grazing resulted in a further reduction to pH 4.5. A significant negative linear relationship (r 2=0.97; P<0.01) was found between increasing soil acidity and dehydrogenase activity. Possible mechanisms influencing these changes are discussed.