Shisham (Dalbergia sissoo Roxb. ex. DC) is grown under flood irrigation on the Indus Plain of Pakistan. This dinitrogen fixing tree enriches the soil in nitrogen and improves the site upon which it is grown. The low C:N ratio, high summer temperatures and irrigation lead to nitrification rates (7.14 mg NO3--N kg-1 soil 24 days-1). In addition, water logging leads to denitrification rates as high or higher than the nitrification rates. Consequently irrigation practices that promote anaerobic conditions through water logging, run the very great risk of removing from the site the nitrogen added through shisham cropping.