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This article in AJ

  1. Vol. 67 No. 2, p. 201-204

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Response Curves of Various Turfgrasses to Application of Several Controlled-Release Nitrogen Sources1

  1. G. M. Volk and
  2. G. C. Horn2



Responses of turfgrasses to controlled-release N sources, especially the newer materials have not been adequately evaluated under field conditions. This study obtained N time-release curves as measured by clippings taken periodically after the initial response to readily available N such products contain had subsided. Materials were suface-applied once, or at widely spaced intervals, to six different turfgrasses. Three to 4-day growth clippings were taken periodically to assess current N uptake rate against that from a standard treatment consisting of a continuous, uniform, weekly application of NH4NO3. Sulfur-coated urea (SCU of 9% dissolution rate) gave the most desirable type of response for summer fertilization, followed by isobutylidene diurea (IBDU), activated sewage sludge (Milorganite), and ureaform (UF). The latter two were quite similar in latent response characteristics. IBDU was superior to the other materials for winterusage, because it did not show the cold weather depression of latent N release exhibited by Milorganite, SCU, and UF. It is postulated that an initial slow N-release rate of IBDU, and the favorable cold weather response curve is the result of the differential effect of temperature on nitritication and, therefore, on acidity and dissolution rate of IBDU in the microenvironment of the pellet. Responses to IBDU of various pellet-size ranges corroborates that surface dissolution is the N-release mechanism, and that varying the pellet size is a valuable method for controlling the N-release rate.

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