Nitrogen mineralization at different moisture levels in soils under wheat–rice cropping systems

Abstract

A study was undertaken to assess the effects of moisture level and time of sampling on nitrogen (N) mineralization in soils under two wheat–rice cropping systems receiving different fertilizer and organic treatments, namely, wheat residue and sewage sludge. The soils (Grey Aeric Haplaquepts) were collected in June and September 1999 from the plots of two on-going experiments at Bangladesh Institute of Nuclear Agriculture (BINA), Mymensingh. Nitrogen mineralization was assayed after 42 days of incubation at 35°C and at 40, 60, and 80% of field capacity. There was no accumulation of ammonium in any of the soils after 42 days of incubation. Net nitrification and the rate of nitrification were found to increase linearly due to increase in moisture content from 40 to 80% of field capacity (FC) in the soil under wheat–rice–fallow (WRF) system. In contrast, a decrease in nitrate accumulation was observed in soil under wheat–fallow–rice (WFR) system due to increase in moisture content from 60 to 80% FC. Again, the September sample of the WFR system showed significantly higher net nitrification and rate of nitrification than those at June. The work suggests that the quantities of active N fractions vary seasonally depending on the additions of fertilizer and organic amendments as well as the environmental factors.