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Agronomy Journal Abstract -

Predicting Nitrogen Fertilizer Requirements After Land Leveling1


This article in AJ

  1. Vol. 66 No. 3, p. 371-374
    Received: July 28, 1973

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  1. J. R. Thomas,
  2. M. D. Heilman and
  3. L. Lyles2



Reduced yields and nutrient-deficient crops on cut areas after land leveling are recognized problems. The objectives of this study were to determine if the variability in crop production between cut and fill areas of leveled fields could be minimized without overfertilization by adjusting the soils to a uniform level of available N based on the soils' capacity to supply N (N index) and to relate the N fertilizer requirement to the N index.

Five leveling methods which resulted in the removal of different amounts of top soil were used. Soils from leveled and nonleveled areas were incubated and the soils' capacity to supply N were described by the regression model N = a + bt1/2, where N is ppm of NO3-N in the soil after t days incubation, and b is the N index. With a 14-day incubation, the nonleveled soils supplied N at the rate of 174 kg/ha. Therefore, based on the leveled soils' ability to supply N in this time period, sufficient NH4NO3 fertilizer was applied to establish N levels of 174, 219, and 263 kg/ha. The leveled fields were cropped to forage sorghum (Sorghum bicolor (L.) Moench).

Dry matter forage yields, N uptake, and the growth rate during the first 19 days of growth were significantly related to the N index. Uniform crop production over the whole area was achieved when the available N level of the top 30 cm of soil was adjusted to 174 kg/ha, except on the conventional leveled soils where all of the top soil was removed. A regression model was developed that expressed the N fertilizer requirement as a function of the N index.

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