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Nitrate in Deep Soil Profiles in Relation to Fertilizer Rates and Leaching Volume¹

ABSTRACT

The NO₃^-N concentration in saturation extracts and soil solutions was determined in 30-m profiles in six treatments of a longterm fertility trial with citrus and in four commercial citrus groves in which the depth of sampling was 15 m or to the top of the water table.

Drainage volumes and excess N in the soil, calculated as N input minus crop removal, provided a reasonable estimate of the NO₃^- concentration of water in the unsaturated zone in open-porous soils when inputs were about 150 kg/ha per year. However, at higher rates of inputs to porous soils or at low rates with soils with profiles which had textural discontinuities, denitrification had to be assumed to obtain a reasonable N balance. Calculated transit times for water to move 30 m in the unsaturated zone varied from 12 to 49 years.

Key Words: Nitrate in soils and waters • leaching fractions • nitrogen balance in soils • water transit time in soils

¹ Contribution of the Department of Soil Science and Agricultural Engineering, in cooperation with the Department of Plant Sciences, University of California, Riverside 92502. Financial support of the Water Quality Office of the Environmental Protection Agency through Grant no. 15060 DOE is gratefully acknowledged.

² Professor of Soil Science, Professor of Horticulture, and former Postdoctoral Fellow, respectively.

Received for publication April 23, 1971.