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The Use of Aqua Ammonia in the Hawaiian Sugar Industry: II. Injection Studies¹

ABSTRACT

The shift from solid forms of nitrogen fertilizer to aqua ammonia has resulted in an annual saving to the Hawaiian sugar industry in excess of $1,000,000. Where reasonably good water distribution is obtained, aqua is successfully applied in the irrigation stream. Results of 35 tests show an average decrease in nitrogen content of 21% as ammoniated irrigation water flows from the head to the tail of 200-foot furrows. About 20% of the decrease was found by tests in plastic lined furrows to be due to volatilization. Ammonia applied in the irrigation water is retained in the top few inches of soil. It is rapidly nitrified, and is then carried downward by subsequent irrigation.

Laboratory studies of aqua ammonia applied directly to the surface of acid soils showed losses up to 15%. In alkaline soils where application rates exceed the ammonia saturation capacity of the soil, volatilization losses can exceed 50% even when placed at depths of 4 inches.

On the unirrigated plantations, aqua is applied by injection at rates of 60 to 200 pounds of N per acre either with the seed at planting, or near the stools at ratooning. Laboratory and field studies show, that at the high concentrations of ammonia obtained by injection, nitrification is retarded. This minimizes loss by leaching and results in effective utilization of the applied nitrogen.

¹ Published with the approval of the Director as Paper No. 46 in the Journal Series of the Experiment Station, Hawaiian Sugar Planters' Association, Honolulu, Hawaii. Presented before Div. IV, Soil Sci. Soc. of America, Cincinnati, Ohio. Nov. 14, 1956.

² Head, Dept. of Agronomy and Senior Agronomist, Exp. Sta., H.S.P.A., respectively.

Received for publication December 4, 1956. Accepted for publication January 29, 1957.