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Distribution of the Forms of Nitrogen in Some Soil Profiles¹

ABSTRACT

This paper presents a preliminary report of studies dealing with the chemistry of the nitrogen in the profiles of different soil types. Total, amino acid, and ammonia nitrogen determinations were made on acid hydrolysates of soil collected from 10 profiles representative of 8 great soil groups. The proportion of amino acid nitrogen to total nitrogen was found to decrease with depth in nearly all of the profiles examined, while the proportion of the nitrogen released as ammonia by acid hydrolysis was found to increase with depth. The magnitude of these changes was dependent on soil type. The results afford an explanation of the well-known phenomenon that the C/N ratio of most soils decreases with increasing depth in the profile. Some practical and theoretical aspects of the findings are considered.

¹ Contribution from the Department of Agronomy, Illinois Agr. Exp. Sta., Urbana, Illinois. This investigation was supported in part by Consolidated Hatch Act Regional Research Funds, as a contributing project to Regional Project NC-17. Presented before Div. III, Soil Science Society of America, Cincinnati, Ohio, Nov. 15, 1956.

² Assistant Professor in Soil Biology. Appreciation is expressed to Miss Mary Louise McKenzie, Mr. Uldis Blukis, Mr. A. P. S. Dhariwal, and Mr. S. M. Savage for performing many of the determinations.

Received for publication December 22, 1956. Accepted for publication January 28, 1957.