Field experiment on long-term application of chemical fertilizers and farmyard manure in floodplain soil of Bangladesh

Field experiment on long-term application of chemical fertilizers and farmyard manure is ongoing in a floodplain soil of Bangladesh since 1978. The treatments are application of N, NP, NK, NPK, NS, NZn, NSZn, NPKSZn, and N+FYM (cowdung as farmyard manure), along with control (no addition), and have been executed in every cropping. Forty-five times of paddy-rice cropping was done before soil sampling in July 2002. Among chemical properties of soil, the organic matter and total N concentrations, clay mineralogical composition, and the heavy metal concentration were assessed. The organic matter and total N concentrations of surface soil were increased from those in the initial state, although this was ascribed to continuous cropping of paddy-rice rather than the direct effect of chemical fertilizers and farmyard manure. Clay mineralogical change, such as fixation of K in the vermiculite interlayer to be transformed into clay mica, was not detected. Accumulation of heavy metals in soil was not noticed.