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Effect of Temperature and Water Quality on Nitrogen Loss from Arizona Irrigation Waters

E. Randall Norton and Jeffrey C. Silvertooth

ABSTRACT

A laboratory study was initiated to investigate the potential loss of fertilizer nitrogen (N) through volatilization at four different temperatures (25, 30, 35, and 40°C) out of irrigation waters collected from a number of Arizona locations. Complete water analysis was conducted on each of the water samples. A 300 ml volume of each water was placed in 450 ml beakers open to the atmosphere in a constant temperature water bath with 10 mg of analytical grade (NH4)2SO4 added to each sample. Small aliquots were drawn at specific time intervals over a 24 hour period and then analyzed for NH4+-N concentrations. Results showed potential losses from volatilization to be highly temperature dependent. Total losses (after 24 hours) ranged from 30-48% at 25°C to over 90% at 40°C. In this study where (NH4)2SO4 was used as the N source, the initial concentration of SO4--S in the solution had a repressive effect on volatilization due to the decreased availability of free NH4+ in waters with high initial SO4--S concentrations due to the formation of complex ion pairs (NH4SO4-). It was also observed that at lower temperatures complexation and ion pair formation affected volatilization of NH3 by reducing the NH4+ activity in solution and thereby reducing NH3 volatilization. Potential volatilization loss of fertilizer N from these irrigation waters was found to be significant and should be considered when making decisions regarding fertilizer N applications for crop production in Arizona.





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Document last modified April 16, 2003