Effects of biotic manipulations and management practices on soil organic carbon, carbohydrates and microbial biomass

Soil organic matter plays important roles in soil fertility. Recent attention has been focused on the soil carbon storage because of its potential as a significant C pool. The objective of this dissertation research is to investigate the effects of plant roots, soil biota and management practices on soil organic carbon, carbohydrates and microbial biomass.; Soils under four biotic treatments (root exclusion, earthworm addition, and inhibition of fungi by fungicide Captan and microarthropods by insecticide Naphthalene) and their untreated controls in the Georgia piedmont after two years were analyzed for total organic carbon, soil nitrogen, microbial biomass C and carbohydrates. Plant roots had the most profound effects on soil carbon, carbohydrates, nitrogen and microbial biomass. Saprophytic fungi substantially contributed to the retention of soil carbohydrates and nitrogen. Root exclusion and inhibition of fungi by a fungicide significantly reduced soil microbial biomass-C, carbohydrates and nitrogen retention. Earthworm additions reduced soil carbohydrates and accelerated soil organic C turnover.; Tillage practices influenced soil organic carbon dynamics. Organic carbon was significantly and consistently higher in no-till surface soils than in conventional-till soils, while no significant differences in organic C of deeper soils were found between two tillage practices after 12 years of continuous treatments. The relative dominance of fungi in no-till systems positively affected the retention of soil carbohydrates. Organic carbon in macroaggregates were more labile than C in microaggregates since the latter had been strongly metabolized by soil microorganisms.; The size of soil labile carbon pools was significantly different among forest and agroecosystems. The highest carbohydrate contents and microbial biomass-C were found in forest soils, but agricultural soils had a higher proportion of the soil organic matter present as carbohydrates and as microbial biomass. Management practices and soil texture significantly affected organic C, carbohydrate contents and microbial biomass-C of agricultural soils. The differences in substrate quality due to different vegetation types substantially influenced labile C pools of forest soils.