The soil biomass as a source of plant nutrients

THE SOIL BIOMASS AS A SOURCE AND SINK OF PLANT NUTRIENTS 6.1 The nutrient content of the soil biomass 

The biomass is a small but comparatively labile part of the organic fraction in soil, and is important as a source and sink of nutrients. Estimates of the amounts of nutrient involved have been made by measuring the biomass-C in soil by various methods, and then assuming the mineral composition of the biomass to be similar to that of laboratory-grown cells. The nutrient content of such laboratory-grown organisms seems rather high. 

Estimation of the nutrient content of the biomass by the fumigation technique is a more direct method, but still assumes that the flushes of nutrients from the killed biomass behave in a similar way to those from the organisms used to estimate the k-factors. At the time of writing there have been comparatively few estimates using the fumigation technique and the majority of these have been on biomass-N. 

The biomass-N comprises roughly the same proportion of total N as the biomass-C does of the total C. Broadbalk unmanured soil was estimated to 

Thus on stockpiled soils biomass-N was only a small proportion of the total 204 

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