Soil Nitrogen Balance in selected Row-Crop Sitesin Southern California
1972
Adriano, D. C. | Takatori, F. H. | Pratt, P. F. | Lorenz, O. A.
Nine row-crop sites, where data for nitrogen fertilizer use, crop yields, and amounts of irrigation water used were available for a number of years, were studied to estimate the N balance as related to NO₃⁻ in water in the unsaturated zone from below the zone of root influence to the water table or to the 15-m depth. The system of predicting NO₃⁻ concentrations in drainage waters based on the difference between N inputs and N removal in harvested crop sand the drainage volume in which the excess N, converted to NO₃⁻, is dissolved, was valid in open-porous soils containing no layers that restrict water movement within the soil profile (0- to 2-m depth). A combination of losses plus net immobilization of up to 56% had to be assumed in some soils to account for all the N loss. In two soils that had been used for disposal of feedlot manure, net mineralization of N from the organic N pool had to be assumed to explain the data obtained. The current fertilization and irrigation practices used for some row crops in southern California leave varying amounts of NO₃⁻ in the drainage water. The amounts depend on the total N added, crop removal, drainage volume, net mineralization, and losses.
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