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Recovery of Residual Nitrogen by Corn (Zea mays L.) from Various Soil Depths as Measured by ¹⁵N Tracer Techniques¹

ABSTRACT

A tracer technique was used to evaluate crop recovery of residual inorganic nitrogen from several soil depths. ¹⁵N-labeled nitrate was placed at depths of 9, 60, 120, and 180 cm in field plots planted to corn (Zea mays L.) and containing 409, 468, and 582 kg inorganic N/ha in the 180-cm profile. Flag leaf samples were collected at three growth stages and their ¹⁵N and total N contents determined.

At early silk stage, no labeled nitrate was extracted from soil at depths below 120 cm, regardless of residual N level. Nitrate was absorbed at the blister stage from a depth of 180 cm in soil containing the lowest amount of residual N. In soil at the highest level of residual N, little labeled nitrate was recovered at any growth stage at depths below 120 cm. At harvest, more ¹⁵N derived from the upper soil profile was found in the stover, while the grain contained considerable ¹⁵N obtained from the middle and lower profiles, presumably related to the later period of uptake.

¹ Published with the approval of the Director as Paper no. 2773 of the Journal Series, Nebraska Agr. Exp. Sta., Lincoln.

² NDEA research fellow; Assistant Professor; Research Chemist, Soils & Fertilizer Res. Branch, TVA, Muscle Shoals, Ala.; and Professor.

Received for publication November 27, 1970. Accepted for publication December 28, 1970.