Leaching and recovery of 15N in dryland and irrigated cropping systems
van Kessel, C.
Peer Reviewed StatusNon-Peer Reviewed
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Laird-lentil and Neepawa-wheat were grown under irrigation in 1987 at the experimental Irrigation Farm at Outlook under three levels of N: 10, 50, and 100 kg of NH4NO3, double labelled with 15N. A similar experiment was conducted at the same site under dry land conditions in close vicinity to the experiment under irrigation. Soil samples to a depth of 120 cm from the plots receiving 10, 50, and 100 kg N/ha were taken at 44, 63, and 101 days after planting, divided into 0-15, 15-30, 30-60, 60-90, and 90-120 cm sections, and analyzed for total N, available N, and atom% 15N. Total recovery of N-fertilizer in the soil decreased through time, irrespective of crop or water regime. While almost no leaching below 15 cm occurred under dry land-lentil, N leached into the 15-30 cm soil zone under dryland-wheat after rain during the last part of the growing season. During that period N accumulation still occurred in lentil but had ceased in wheat at final harvest and under irrigated conditions, 9 % of N applied (100 kg N/ha) had leached below 30 cm when the soil was cropped with lentil and 7 % when cropped with wheat. Regardless of the amount of N applied, moisture regime, or crop grown, a minimum concentration of available soil-N of around 8 ppm (150 kg N/ha to a depth of 120 cm) was always present It appeared that in this study mineral soil-N became only available for plant uptake when the mineral N concentration exceeded 8 ppm. The amount of total available soil N in the form of NH4+ remained constant in the dryland soil. However, under irrigation there was a sharp increase in the amount of NH4+. Lack of O2 in the water-saturated top soil reduced nitrification activity and NH4+ levels increased. On average, total fertilizer-N recovered in plant and soil was 50 %, regardless of crop or water regime, and remained fairly constant throughout the growing season. However, percent N-fertilizer recovered in the soil decreased and the percent fertilizer-N recovered in the plant increased over time. Possible N-losses can be attributed to denitrification, nitrification, ammonia volatilization, and/or NH4+ fixation. The percentage of 15N-fertilizer recovery found in this study agrees with other published data from Saskatchewan.
Part OfSoils and Crops Workshop
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