INFLUENCE OF VEGETABLE INCLUSION IN RICE MONOCULTURE ON SOIL ORGANIC MATTER QUALITY UNDER SUB-TROPICAL CLIMATE

Abstract

Soil organic matter (SOM) quality and iits decomposibility is influenced by cropping pattern. However, little is known on this matter, particularly so far rice monoculture or comination of vegetables with rice culture. Therefore, four pairs of fields having vegetable-rice and rice-rice cropping pattern were selected from four different locations in Bangladesh, covering floodplain and terrace soils. Soils were first physically fractionated into particulate organic matter (POM) and silt and clay sized OM. The silt and clay sized OM was further chemically fractionated by oxidation with 6% NaOCl to isolate an oxidation-resistant OM fraction, followed by extraction of mineral bound OM with 10% HF (HF-res OM). The results show that there is a small increase in POM in vegetable compared with rice soils. Among the chemical treatments, NaOCl oxidized the largest amount of OC and N from the silt and clay fractions of vegetable soils. The silt and clay N in vegetable soil was found to be more susceptible to NaOCl treatment compared with OC. Both the HF-extracted (HF-ex) and HF-res OM fractions were found to be lower in vegetable soils compared with rice soils. Results from both physical and chemical fraction of SOM suggest that SOM accumulated in vegetable-rice cropping pattern are more labile than the solely rice based cropping pattern and prone to decompose quickly in any change of land use.