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Availability of Nitrogen from Crop Residues during the First and Second Seasons After Application¹

ABSTRACT

The availabilities of nitrogen in alfalfa tops, red clover tops, soybean straw, and oat hulls were compared at different rates of application with the availability of nitrogen from ammonium nitrate. The initial applications were made and evaluated on corn but the carry-over effects in the second cropping season were measured with an indicator crop of oats.

During the first cropping season, freshly cut alfalfa tops were more efficient in increasing corn yield than equivalent rates of application of red clover. Soybean straw had little or no influence on corn yield and oat hulls tied up soil nitrogen and resulted in decreases in corn yield. On the basis of pounds per acre of nitrogen applied, the mean efficiency of alfalfa in supplying nitrogen to the corn crop was only about 34% of that of ammonium nitrate.

Nitrogen availability from the residues during the second growing season was not more than 7.5% of that originally contained in alfalfa and 3.5% of that contained in red clover. About 2% of the original nitrogen from soybean straw appeared to be available during the second cropping season, but none of the nitrogen from the oat hull applications. Only where large amounts of residue had been applied to corn the first season were the carry-over effects measurable during the second season.

¹ Contribution from the Department of Agronomy, Iowa Agr. Exp. Sta. Journal Paper J-2894, project 1205 of the Iowa Agr. Exp. Sta., Ames, Iowa. Presented before Div. III, Soil Science ociety of America, Davis, Calif., Aug. 16, 1955.

² Graduate assistant and Professor, respectively, in the Agronomy Department. The latter is now with the Soils Dept., North carolina State College, Raleigh.

Received for publication February 1, 1956.