Effects of land use and management practices on quantitative changes of soil carbohydrates

Abstract

Soil carbohydrates (SC) are important parameters in determining soil fertility in different land uses, particularly in the tropics. There are no tropical studies reported so far on the effect of heterogeneneous land uses on the concentration of SC. Therefore, SC under 13 different land uses including forests and adjacent cultivated lands in Sri Lanka were studied. Soil litter (SL) and soil organic C fractions were evaluated for availability of SC. The study showed that SL is the main factor determining SC composition. Positive relationships between SL and carbohydrates of plant origin (CPO) indicated that SL is the major source of carbohydrates in cultivated lands. Negative relationships were observed between SL and carbohydrates of microbial origin (CMO) in forests. Although the vegetation structure differs, the forests did not show much variation in SC, as soil disturbances, which lead to differences in decomposition rates were minimal or absent. However, the soil management practices among the cultivated lands were highly variable and hence induced significant variations in SC by changing the litter decomposition processes. Intensive soil tillage, agrochemical use and low biomass return reduced the SC to a significant level as shown in potato and tea soils. Three carbohydrates, namely arabinose, xylose and glucose, were not detected in potato cultivation, while ribose and glucose were not detected in tea plantation. The concentration of the other carbohydrates was restricted to the range of 0.12 - 1.75 × 10-6 g kg soil-1 in tea. High biomass return and minimum soil tillage in rubber and coconut plantations respectively increased the SC to 48.6 and 57.79 × 10-6 g kg soil-1 being comparable to their adjacent forests. By comparing SC of forests and the adjacent cultivated lands, both having similar climatic conditions and soil types, the study confirmed that differences in land management practices affected SC concentration. This study provides important guidelines for selecting better land management practices in tropical ecosystems for sustaining soil fertility through SC management.