The initial phase of the project was devoted to the selection and testing of analytical techniques for assessing total nitrogen and leaching losses, and gaseous losses of nitrogen by ammonia volatilization and denitrification following the application of urea to cotton. Total nitrogen loss was measured in microplots by determining the amounts of labelled fertilizer nitrogen recovered in plants and soil, and subtracting this from the amount originally applied. Ammonia loss was determined directly by a micrometerological technique which determines the ammonia concentration gradient in the air above the cotton crop. Denitrification loss was calculated by subtracting the measured ammonia loss from the total nitrogen loss. The movement of 15N down the soil profile gave an indication of the importance of leaching loss.