Nitrogen fertilizer use and losses in irrigated cropping systems

Non-Peer ReviewedThe fertilizer-N use efficiency of irrigated canola, softwheat, durum, and spring wheat was determined in 1988 and 1989. Crops received various amounts of N, applied at time of seeding or split between time of seeding and during the growing season. In 1989 at two sites, Outlook and Birsay both located on a field owned by farmers, N-losses due to denitrification after irrigation were determined by means of acetylene blockage. Softwheat and durum were grown at Outlook and Birsay, respectively. In 1988, all treatments received 150 kg N/ha, split equally between time of seeding and 54 days after planting. In 1989, all crops received 200 kg N/ha, applied at time of seeding or split equally between time of seeding and during the growing season. Fertilizer use efficiency (% FUE) in the crop of irrigated canola in 1988 averaged 37 % in the soil at time of final harvest. In 1989 the average FUE in canola was 27.4 %, in softwheat 42.3 % and in durum 43.0 %. The % FUE was 22 and 21 % at Birsay and Outlook, respectively. Nitrogen losses caused by denitrification were small at one site but significant at another. At the site with low input of N and irrigation water the N-losses were practically zero before the onset of irrigation, increased to a maximum loss of 50 g N/day/ha at 4 h after irrigation and declined to low levels at 10 h after irrigation. At the other site, with high N and irrigation water, the N losses from fertilized soil due to denitrification were approximately 5 kg N/day/ha, increased to 12.5 kg N/day/ha at 4 h after the application of water and declined to approximately 5 kg N/day/ha at 10 h after the water was applied