Leaching and Crop Uptake of Nitrogen from Nitrogen-15-Labeled Green Manures and Ammonium Nitrate
- Lars Bergström * and
- Holger Kirchmann
Green manures can be used as an N source for agricultural crops as a substitute for inorganic N fertilizers. The effects of using green manures on leaching and uptake of N by spring barley (Hordeum vulgare L.) were evaluated in a 2-yr lysimeter study. Ryegrass (Lolium perenne L.) and red clover (Trifolium pratense L.) labeled with 15N were applied in May of the first year at 160 kg total N ha−1 Simultaneously, 15NH4 15NO3 was applied at 80 kg N ha−1 to additional lysimeters and others were left without N additions (control). During the second year, all lysimeters, except the control, received 80 kg N ha−1 as unlabeled NH4NO3 The cumulative, average loads of total N leached during the two years were: 37 (control), 62 (NH4NO3), 50 (ryegrass manure), and 73 (red clover manure) kg ha−1 The differences among the treatments were not significant (P > 0.05), but the control had significantly smaller (P < 0.05) leaching loads than the treatments. About 24% of ryegrass- and red clover–derived N and 43% of NH4NO3 were removed through spring barley grain and stover during the two growing seasons. Thus, the N use efficiency in barley was substantially larger when grown with inorganic N fertilizer than when grown with green manure. Viewed in combination with the tendency for larger N leaching loads under red clover manure, claims about water quality benefits of legume-based green manures should be evaluated with regard to the timing of N release and demand for N by the plant.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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