Phosphorus in the soil microbial biomass |
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Authors: | PC Brookes DS Powlson DS Jenkinson |
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Institution: | Rothamsted Experimental Station, Harpenden, Herts. AL5 2JQ, England |
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Abstract: | Phosphorus in the soil microbial biomass (biomass P) and soil biomass carbon (biomass C) were linearly related in 15 soils (8 grassland, 6 arable, 1 deciduous woodland), with a mean P concentration of 3.3% in the soil biomass. The regression accounted for 82% of the variance in the data. The relationship was less close than that previously measured between soil biomass C and soil ATP content and indicates that biomass P measurements can only provide a rough estimate of biomass C content. Neither P concentration in the soil biomass, nor the amount of biomass P in soil, were correlated with soil NaHCO3-extractable inorganic, organic or total P.The calculated mean annual flux of P through the biomass (in a soil depth of 10 cm) in 8 grassland soils was large, 23 kg P ha?1 yr?1, and more than three times the mean annual P flux through 6 arable soils (7 kg P ha?1 yr?1), suggesting that biomass P could make a significant contribution to plant P nutrition in grassland.About 3% of the total soil organic P in the arable soils was in microbial biomass and from 5 to 24% in the grassland soils. The decline in biomass P when an old grassland soil was put into an arable rotation for about 20 yr was sufficient to account for about 50% of the decline in total soil organic P during this period. When an old arable soil reverted to woodland, soil organic P doubled in 100 yr; biomass P increased 11-fold during the same period. |
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