Soil quality in mangrove ecosystem deteriorates due to rice cultivation

Abstract

In this paper an attempt has been made to quantify and test whether rice cultivation in adjoining areas of mangrove forest by cutting forest tress has brought about significant changes in physicochemical, microbial and enzymatic properties of soils of the mangrove ecosystem. We collected 48 soil samples (24 pairs). We collected paired soil samples from each location, i.e., one soil sample from mangrove forest and its paired soil sample from adjacent rice fields. Various soil physicochemical, microbial and enzymatic properties were analyzed. Total soil organic carbon (TOC), available potassium and Bray P were significantly higher in soils of mangrove forest than soils of cultivated rice fields. Soil pH was in the acidic range at all locations, but was moderated towards neutral in mangrove soils. DTPA extractable concentrations of soil micronutrients (Zn, Mn) were significantly higher under the soils of mangrove than soils under cultivated rice fields. Enzymatic activities (Dehydrogenase, Urease, FDA hydrolysis, Acid Phosphatase) in soils of mangrove forests exceeded than under cultivated rice fields except for acid phosphatase activity which had higher activity in soils of cultivated rice fields. Populations of ammonium oxidizer and nitrite oxidizer were higher in mangrove soils, whereas populations of aerobic hetreotrophs were higher in cultivated rice fields compared to mangrove soils. The study provides a soil quality index based on soil physico-chemical and microbiological properties. This index is a function of the eight soil parameters, which showed the greatest weight in the factorial analysis made with all the parameters analysed. The value of the soil quality index was higher in mangrove soils compared to soils of rice fields at all the four locations of sampling indicating the adverse effect of rice cultivation around the mangrove forests.