Seasonal responses in microbial biomass carbon, phosphorus and sulphur in soils under pasture |
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Authors: | Z L He J Wu A G O‘Donnell J K Syers |
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Institution: | (1) Department of Agricultural and Environmental Science, University of Newcastle, Newcastle Upon Tyne, NE1 7RU, UK Tel: (191)222-5677; Fax: (191)222-5677, GB |
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Abstract: | The response of the soil microbial biomass to seasonal changes was investigated in the field under pastures. These studies
showed that over a 9-month period, microbial biomass carbon, phosphorus and sulphur (biomass C, P, S), and their ratios (C:P,
C:S, and P:S) responded differently to changes in soil moisture and to the input of fresh organic materials. From October
to December (1993), when plant residues were largely incorporated into the soils, biomass C and S increased by 150–210%. Biomass
P did not increase over this time, having decreased by 22–64% over the dry summer (July to September). There was no obvious
correlation between biomass C, P, and S and air temperature. The largest amounts of biomass C and P (2100–2300μg and 150–190μgg–1 soil, respectively) were found in those soils receiving farmyard manure (FYM or FYM+NPK) and P fertilizer, whereas the use
of ammonium sulphate decreased biomass C and P. The C:P, C:S, and P:S ratios of the biomass varied considerably (9–276:1;
50–149:1; and 0.3–14:1, respectively) with season and fertilizer regime. This reflected the potential for the biomass to release
(when ratios were narrow) or to immobilize (wide ratios) P and S at different times of the year. Thus, seasonal responses
in biomass C, P, and S are important in controlling the cycling of C, P, and S in pasture and ultimately in regulating plant
availability of P and S. The uptake of P in the pasture was well correlated with the sum of P in the biomass and soil available
pools. Thus, the simultaneous measurement of microbial biomass P and available P provide useful information on the potential
plant availability of P.
Received: 25 May 1996 |
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Keywords: | Seasonal responses Microbial biomass C Microbial biomass P Microbial biomass S Nutrient cycling Pasture |
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