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This article in AJ

  1. Vol. 68 No. 6, p. 933-937
    Received: Jan 8, 1976

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Grass Hay Production as Influenced by N-P Topdressing and by Residual P1

  1. A. E. Ludwick and
  2. C. B. Rumburg2



Information is limited on the response of grass to top dressing N-P combinations on soils deficient in both nutrients, especially concerning time of application. The purpose of this study was to compare fall and spring topdressing of N-P combinations for grass hay production and to evaluate residual P during succeeding seasons.

A 4-year experiment was conducted on a Fola cobbly sandy clay loam soil (Borollic Camorthid) near Gunnison, Colorado. Vegetation consisted of a mixed stand of bromegrass (Bromus inermis Leyss.), timothy (Phleum pratensis L.), orchardgrass (Dactylis glomerata L.), bluegrass (Poa pratense L.), and occasional plants of red clover (Trifolium pratense L.). Treatments were 4 rates of both N and P applied either in the fall or spring, prior to the first growing season. Residual P was evaluated the following three seasons.

Hay yields the 1st year (1972) were significantly increased from 2.51 metric tons/ha with no fertilizer to 10.77 for the highest fertilizer combination of 358 and 59 kg/ha of N and P fall applied. Yields increased with increasing rates of both nutrients. Yields from fall a p plied N-P combinations averaged 1.0 to 2.5 metric tons/ha greater than yields from similar treatments spring applied. Apparently the additional time and opportunity for dissolution of the P granules and movement through the thatch and into the surface soil resulted in the fall treatments being superior to similar treatments spring applied. Uptake of both N and P followed trends similar to yields. Yields in 1973 and 1974 were increased over the control (O-P) by the initial P treatments, although yields and P uptake declined each year. Time of initial fertilizer application (fall vs. spring) did not significantly affect yields nor P uptake beyond the first season.

Although residual P continued to increase yields and P uptake in 1975 (significant over the control at the highest P rate), reapplying P significantly increased both over all residual P levels.

Bicarbonate extractable soil P levels were markedly increased in the upper 2.5 cm of soil by P topdressing. There was no evidence of P movement below 5.0 cm.

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