Potentially mineralizable nitrogen in ten important sub-tropical soil series of Bangladesh

Abstract

Knowledge on nitrogen (N) supplying capacity of inherent soil organic matter helps farmers and extension workers to determine the N fertilization rate. However, this information is very scanty particularly in developing countries like Bangladesh. Thus, this research work was conducted to estimate potentially mineralizable nitrogen (N) in ten important soil series of Bangladesh namely Jamalpur, Silmondi, Sonatala, Ghatail, Tejgaon, Chandra, Khilgao, Kalma, Brahmaputra and Sherpur. Net N mineralization in these soil series was measured during 100 days laboratory incubation at 20⁰C at field capacity. Findings revealed that eight out of ten soil series had silt loam texture and the rest two were loams. All soils were slightly acidic in reaction. The organic carbon and total N contents of the soils varied from 5.24 to 17.4 and 0.53 to1.48 g kg soil^-1, respectively with the C:N ratios of 9.89 to 11.76. The amount of net N mineralization and nitrification (NO₃^-1-N) increased linearly with time; however, ammonification (NH₄⁺-N) did not follow any definite trend. Majority of mineralized N undergone nitrification falling within the ranged between 30 and 128 mg/kg soil/98 days. The net N mineralization (mg NH₄⁺-N+NO₃^-1-N kg^-1 soil) varied from 51 mg N kg^-1 soil in Tejgaon soil series to 154 mg N kg^-1 soil in Khilgaon soil series accounting for 4.3 to 10.8% of total N mineralized 120 days^-1. The rate of N mineralization also varied widely from 1.19 to 0.28 (mg N kg^-1 soil day^-1) like the net N mineralization. The highest rate of N mineralization was observed in Khilgaon soil series followed by Chandra, Ghatail, Silmondi, Sherpur, Jamalpur, Sonatola, Kalma, Bramaputra silt and Tejgaon soil series. N mineralization was significant and positively correlated with organic carbon and total N and NH₄^{+ -}N contents of soils. Khilgaon and Chandra soil series have shown greater potentiality in supplying nitrogen under aerobic condition.