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Nitrogen Status of Marshall Silt Loam as Influenced by Different Crop Rotations¹

ABSTRACT

A study to compare the effects of several different crop rotations on crop yields and on certain physical and chemical properties of the Marshall silt loam soil has been underway since 1942. The objective in the present study was to evaluate the relative nitrogen status of the plots planted to corn in 1951 as revealed by content of soil organic matter and total nitrogen, nitrification studies, and nitrogen content of the corn leaf.

Corn plots, in rotations which included one or more years of meadow, contained significantly higher amounts of organic matter and nitrogen than did plots in the corn-oats rotation, although the differences were only 0.2 to 0.3% organic matter. Considering all rotations, the correlation between corn yields and organic matter content of the soil was not significant (r = .47); the relation between yields and total nitrogen, however, was significant (r = .64).

Marked differences in yield between first- and second-year corn occurred in various rotations, although the organic matter content of these plots were the same, as might be expected. On the other hand, nitrate release on incubation of soils and content of leaf nitrogen clearly reflected the relative nitrogen availability under first- and second-year corn.

Considering all rotations, a highly significant relation was found between corn yields and nitrogen content of the sixth corn leaf (correlation coefficient (r) = 0.97). A less striking, although highly significant, relationship occurred between nitrate released during a 2-week incubation period and corn yield (r = 0.78). The value of studying leaf nitrogen as well as nitrification rate as a means of periodically evaluating the soil nitrogen status in rotation experiments is discussed and illustrated in this paper.

¹ Journal Paper No. J-2225 of the Iowa Agr. Exp. Sta., Ames, Iowa, Project 1205. Joint contribution of the Agronomy Dept., Iowa State College, and the Division of Research, Soil Conservation Service, U. S. D. A. Presented before Division IV, Soil Science Society of America, Cincinnati, Ohio, Nov. 19, 1952.

² Former Graduate Student, Professor of Soils and Soil Conservationist, respectively.

Received for publication February 9, 1953.