Nitrogen Leaching Losses from Irrigated Orchardgrass on Sandy Soils
- D.G. Watts *,
- G.W. Hergert and
- J.T. Nichols
Irrigated pasture may provide an alternative forage source for livestock producers in Nebraska's Sandhills. As with any heavily fertilized crop, there is a significant potential for groundwater contamination by nitrate nitrogen (NO3-N) leached from the crop root zone. A 3-yr experiment was conducted in West Central Nebraska to evaluate water and nitrate (NO−3) leaching losses from irrigated orchardgrass (Dactylis glomerata L.) seeded on a Valentine fine sand (Typic Ustipsamments). Three irrigation levels (slight deficit, slight excess, and excess) and four N amounts (0, 112, 224, and 336 kg−1) were applied. Deep percolation and NO−3 leaching were measured with Duke-Haise trough-type extractors. All irrigation treatments had more deep percolation than expected, as the crop coefficient used for irrigation scheduling proved to be too large. The deficit irrigation treatment served as a “close management” treatment since percolation was minimal and yield was not reduced by water stress. During the first 2 yr of operation, in-season percolation losses averaged 7, 28, and 47 cm yr−1 for low, medium, and high irrigation levels, respectively. Total in-season NO3-N leaching loss for the same period ranged from 6 to 228 kg ha−1, depending on N and irrigation amount. Winter and early spring N leaching losses, as estimated by soil sampling, were a significant part of total N loss. Under reduced inseason drainage and an N rate commensurate with 80 to 85% of maximum production, a minimum annual N leaching loss of 35 kg ha−1 can be expected. Greater losses are probable under average water and N applications and average management skills.
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