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Chemical and Biochemical Considerations for Maximizing the Efficiency of Fertilizer Nitrogen¹

ABSTRACT

Fertilizer nitrogen is subject to loss from the soil-root zone, and immobilization by the soil and rhizosphere microfloras, which can result in low recovery and use efficiency of the applied nitrogen. With increasing rates of application, fertilizer nitrogen efficiency decreases progressively, while leaving an increasing amount of unused nitrogen as a potential pollution hazard. Since the point of greatest economic return from this nutrient is usually somewhere below the point of maximum yield, it should be possible to adjust fertilizer nitrogen rates for maximum return and minimum loss to the environment. This can be achieved through improved soil and crop management practices, including proper timing of application of conventional nitrogen fertilizers and use of deep-rooted crops for recovery of leached nitrate. A rational approach to more meaningful nitrogen recommendations is needed, one which would account for residual fertilizer nitrogen and mineralizable soil nitrogen, and allow an accurate prediction of the amount of supplemental fertilizer nitrogen necessary to produce the desired yield. Efficiency of fertilizer nitrogen might also be increased with controlled release fertilizers, including the use of coated granules, and compounds of limited water solubility blended with conventional nitrogen fertilizers, to achieve a specific release rate coincident with the nitrogen requirements of a crop. Formulation of ammoniacal fertilizers with nitrification inhibitors offers considerable opportunity for increasing fertilizer nitrogen efficiency.

Key Words: controlled release fertilizer • nitrification inhibitors • ground water pollution

¹ Contribution from the Agricultural Research Service, U. S. Department of Agriculture, cooperating with the Louisiana Agr. Exp. Sta., Baton Rouge, La. 70803.

² Microbiologist.