Fate of Nitrogen-15-Labeled Fertilizer Nitrogen in Revegetated Cretaceous Coal Spoils1
- J. D. Reeder2
Western wheatgrass (Agropyron smithii L.) was grown in a greenhouse study on two Cretaceous coal spoils and a topsoil to describe the short-term behavior of several levels of added 15N-labeled (NH4)2SO4 (0, 60, 120, and 240 mg N kg−1 soil). Recovery and distribution of fertilizer N was measured at harvest in the soil materials and in the harvested tops, roots, crowns, and rhizomes of the western wheatgrass. Fertilizer N uptake by plants grown in the topsoil increased significantly with increasing fertilizer rate, but a significant increase in aboveground biomass did not occur with the 240 mg N kg−1 treatment. In contrast, aboveground biomass on the two spoils increased significantly with the addition of 60 mg N kg−1, but additional increases in plant biomass with higher fertilizer rates did not occur, and a significant decrease in plant biomass occurred with the 240 mg N kg−1 treatment. Significantly lower water holding capacities and cation exchange capacities resulted in significantly higher NH4+ concentrations in solution in the spoil materials as compared with the topsoil. Thus, suppressed seedling emergence and establishment in the spoil materials was attributed to NH3 toxicity and/or phytotoxicity due to NO2− accumulation in the spoil. Substantial fractions of added fertilizer N (65–72%) were immobilized by the plants and into soil organic matter in the topsoil, and only at the highest fertilizer rate did fertilizer N accumulate in mineral form. Under field conditions, this immobilized N should be available for recycling and plant uptake in subsequent years and thus help reestablish a functional N-cycling ecosystem. In comparison, percent recovery of added N decreased in plant biomass and increased in NO3− form in the two spoils as the rate of fertilizer application increased. Thus, 40 to 50% of added fertilizer N could be susceptible to leaching losses under field conditions.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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