Leaching and crop uptake of nitrogen from nitrogen-15-labeled green manures and ammonium nitrate.
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 (15)N were applied in May of the first year at 160 kg total N ha(-1). Simultaneously, (15)NH(4)(15)NO(3) 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 NH(4)NO(3). The cumulative, average loads of total N leached during the two years were: 37 (control), 62 (NH(4)NO(3)), 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 NH(4)NO(3) 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.
Bergström
Lars
L
Department of Soil Sciences, Swedish University of Agricultural Sciences, P.O. Box 7072, SE-75007 Uppsala, Sweden. lars.bergstrom@mv.slu.se
Kirchmann
Holger
H
D000383:Agriculture; D005308:Fertilizers; D001467:Hordeum / Q000737:chemistry; D008129:Lolium / Q000737:chemistry; D008372:Manure; D009566:Nitrates / Q000737:chemistry; D009584:Nitrogen / Q000032:analysis / Q000493:pharmacokinetics*; D009587:Nitrogen Isotopes / Q000032:analysis; D012995:Solubility; D029921:Trifolium / Q000737:chemistry
D005308:Fertilizers; D008372:Manure; D009566:Nitrates; D009587:Nitrogen Isotopes; D009584:Nitrogen; C006568:ammonium nitrate