Mineral nitrogen forms and availability in major soil groups of Orissa as influenced by water regime

Abstract

An experiment was conducted during 2000 to determine forms and availability of mineral nitrogen at Bhubaneshwar, in 12 soils under 5 water regimes, viz 20, 40, 60, 80 and 100% saturation. The NO₃-N dominated at -< 40 % saturation, whereas NH₄-N dominated at -> 60% saturation. Averaged over the soils, mineral N availability was the lowest at 60-80% saturation. The N availability incieased when soil moisture fell below 60 % or rose above 80 % saturation. Averaged over the water regimes, mineral N availability Was lower in Inceptisols (9.7-14.0 mg N/kg soil) than in Entisols (17.9-19.7 mg N/kg soil) and Alfisols ( 17.8-32.3 mg N/kg soil). The mineral N availability at 40-100% saturation was negatively correlated with pH and electrical conductivity (Be) of soil. In soils at 100% saturation, where mineral N was in NH₄ form, the dependence of N availability on pH as well as EC was best described by power-type equations. In partially saturated soils, where mineral N Was either in NO₃ or in NO₃ plus NH₄ forms, the dependence of N availability on pH was best described by simple linear equations, whereas quadratic equations described well the EC-N availability relationships in the soils.