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Nitrogen and Sulfur Content and pH of Precipitation in Iowa¹

ABSTRACT

Ammonium-N, nitrate-N, sulfate-S, and phosphate-P concentrations, along with pH of precipitation samples, were measured at six sites in Iowa from Sept. 1971 through Dec. 1973. The amounts of nutrient constituents added by precipitation were determined. The annual amounts of NH₄-N and NO₃-N added by precipitation at each site were about equal. The annual amounts of inorganic N added per hectare ranged from 10 kg in north-central to 14 kg in west-central Iowa, and the annual amounts of SO₄-S added per hectare ranged from 13 kg in northeastern to 17 kg in north-central Iowa. It was estimated that, on an average basis, precipitation adds about 0.6 kg of NH₄-N, 0.6 kg of NO₃-N, and 1.5 kg of SO₄-S per hectare monthly in Iowa. However, seasonal variations were observed for SO₄-S, higher during fall and winter than during spring and summer.

Average annual pH value of the rainfall and snowfall samples collected at each site during each year was about 6; individual samples were seldom as low as pH 4. The data indicated that the P content of precipitation is very small; at the most about 0.1 kg of water-soluble PO₄-P was added per hectare annually, Nitrite-N was not detected in any of the precipitation samples analyzed.

Key Words: air pollution • phosphorus • rainfall • snowfall • water quality • ammonium • nitrate • nitrite • sulfate

¹ Journal Paper J-8178 of the Iowa Agric. & Home Econ. Exp. Sta., Ames, IA 50010, Project 1845; and the North Central Region, Agricultural Research Service, USDA.

² Associate Professor, Dep. of Agronomy, Iowa State Univ., and Agricultural Engineer, USDA-ARS, respectively.

Received for publication June 2, 1975.