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The Effects of Corn Residue, Nitrogen, and Incubation on Nitrogen Release and Subsequent Nitrogen Uptake by Oats: A Quantitative Evaluation¹

ABSTRACT

A fertile Clarion loam soil was treated with rates of corn residue and nitrogen and incubated at approximately 30° C. for different periods under controlled moisture conditions. After incubation, half of the treated soils were leached to remove the soluble nitrogen. Inorganic nitrogen determinations on the leachate were used to study the effects of the treatments on nitrogen release.

Regression equations were used to express inorganic nitrogen yield as a function of time. The first derivatives of these equations were used to estimate the time, in days, at which the "maximum" inorganic nitrogen immobilization or minimum amount of soluble nitrogen occurred for each level of nitrogen. These time values were used to estimate the maximum quantities of nitrogen immobilized at each nitrogen level. The results indicate that in fallow-incubated soils that had received residue, the "maximum" quantity of inorganic nitrogen immobilized increased as the quantity of applied nitrogen was increased. However, after the estimated minima of the curves were passed, the net rate of mineralization also increased with the rates of nitrogen.

The leached and unleached soils were cropped with oats, which was harvested at the boot stage. Dry matter yield and nitrogen yield curves were used to evaluate the various treatment effects. The results indicate marked responses to the residue, nitrogen, incubation, and leaching treatments. The various yield curves indicate that the immobilized nitrogen was released to the crop.

The leaching technique used in this experiment is shown to be an excellent method for evaluating net nitrogen transformations. This technique may have applicability in studying other mobile soil nutrients and also, the effects of applied fertilizers on the release of other soil or fertilizer nutrients.

¹ Journal Paper No. J-3302 of the Iowa Agr. and Home Econ. Exp. Sta., Ames, Iowa. Project No. 1189. Contribution from the Department of Agronomy. Presented before Div. IV, Soil Science Society of America, Atlanta, Ga., Nov. 19, 1957. Part of a thesis submitted in partial fulfillment for the Ph.D. degree by the senior author. The research was supported in part by a grant from the Spencer Chemical Company.

² Former Graduate Assistant in Soils, now Agricultural Economist, Tennessee Valley Authority, and Associate Professor of Soils, respectively.

Received for publication February 13, 1958. Accepted for publication May 23, 1958.