Effects of sieving on estimations of microbial biomass, and carbon and nitrogen mineralization, in soil under pasture

Abstract

Biochemical indices of microbial biomass and other biochemical properties of a Typic Haplaquoll, sampled under pasture over four seasons, were compared in intact cores and soil sieved through a 6 mm and a 2 mm mesh. Sieving had an inconsistent influence on biomass C estimates, which tended, however, to be higher in <2 mm-mesh than in <6 mm-mesh soil. Sieving had no deleterious effect on mineral-N flush values, and no significant effect on biomass P, and generally adenosine 5'-triphosphate (ATP), contents. Judged by the values of biomass C/ATP and biomass C/mineral-N flush ratios, the biomass C estimates of winter samples, collected under water-logged conditions, were unrealistically low, particularly in sieved soil. CO2 production by soil at a standardized water potential tended to be lowest in <2 mm-mesh samples. In contrast, net mineralization of N, in all except the winter <2 mm-mesh soil, was highest in sieved soil, as generally were extractable inorganic and organic P contents. Overall, sieving is considered preferable to the use of intact cores for measurements of these biochemical properties in soil under pasture.