Turnover of root-derived material and related microbial biomass formation in soils of different texture

Abstract

Wheat plants were grown on two soils of different texture, a sandy soil and a silty clay loam, in an atmosphere containing 14CO 2. The 14C and total C content of the shoots, roots, soil rhizosphere CO 2 and soil microbial biomass were measured 21, 28, 35 and 42 days after germination. There was a pronounced effect of soil texture on the turnover of root-derived C through the microbial biomass. Turnover was relatively fast and at a constant rate in the sandy soil but slowed down in the clay soil, following an initial high assimilation of root products into the microbial biomass. Four percent of the total fixed 14C was retained in the clay loam after 6 weeks compared with a corresponding value of 1.2% for the sandy soil. The proportion of fixed 14C recovered as rhizosphere CO 2 at each of the sampling times was relatively constant for the sandy soil ( ca 19%) but decreased from 17% at day 28 to 11% at day 42 in the clay soil. The proportion of total fixed 14C in the soil biomass as measured by a fumigation technique increased to a maximum value of 20% after 6 weeks in the sandy soil but decreased in the clay soil from 86% at day 21 to 26% after 42 days plant growth.