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Correlation Between Nitrifiable Nitrogen and Yield Response of Corn to Nitrogen Fertilization on Iowa Soils¹

ABSTRACT

Nitrification rate is proposed as a procedure for evaluating nitrogen requirements of soils for the production of corn. By the use of a modified nitrification method the rate of nitrate production was compared with the response of corn to nitrogen fertilizer in a series of experiments conducted in Iowa over a period of seven years. A significant correlation was obtained between nitrification rate and the response of corn to the application of 40 to 60 lbs. of nitrogen per acre. The data serve to stress the influence of plant population density on the magnitude of yield response to nitrogen. At comparable rates of nitrification considerably higher yield responses to fertilization were obtained where the plant population was high than where it was low. In all population groups, however, a profitable yield response to nitrogen fertilization was obtained where the nitrification rate was less than 40 ppm. On fields with thick stands, profitable yield increases were generally obtained when the nitrification rate was less than 50 ppm.

¹ Journal paper J-2193 of the Iowa Agricultural Experiment Station, Ames, Iowa. Project 1190. Presented before Division IV, Soil Science Society of America, Cincinnati, Ohio, November 19, 1952.

² Formerly Assistant Professor, Associate Professor, and Technician in Soils, respectively.

Received for publication December 12, 1952.