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Nitrification of Ammonium Sulfate in a Calcareous Soil as Influenced by Combinations of Moisture, Temperature, and Levels of Added Nitrogen¹

ABSTRACT

(NH₄)₂SO₄ at levels of 0, 150, and 450 ppm. N was incubated in a calcareous soil at 2°, 10°, and 22° C. at 10, 1, and 0.3 bars moisture tension using periodic aeration. A second incubation study included 4 other moisture levels (7, 15, 115, and 415 bars moisture tension) and continuous aeration. Good control of the moisture was attained with the continuous aeration by humidifying the incoming air over saturated salt solutions known to give the required relative humidity. The soil used, Millville loam from the Agronomy farm, is a highly calcareous (47% CaCO₃ equivalent) fertile soil with a saturated paste pH of 7.8, and moisture contents at field capacity (0.3 bar tension), permanent wilting percentage (15 bars tension), and air dry of 18.0, 6.9, and 1.6%, respectively.

The only evidence of nitrification at 2°C. was the production of NO₂-N which was not converted to NO₃-N in 10 weeks. At 10°C. there was nitrification at , 1, and 10 bars tension where the lowest moisture (10 bars tension) apparently only delayed the initiation of nitrification and did increase the period of NO₂-N accumulation. At 25°C. nitrification was completely inhibited at 415 and 115 bars tension. At 15 bars tension 50% of the 150 ppm. N was oxidized to NO₃-N in 28 days, while at 10, 7, and 1 bars tension the nitrification was complete in about 28, 20, and 12 days. In this soil, 35°C. was less favorable for nitrification than 25°C. NO₂-N accumulated at this temperature and persisted throughout the 8 weeks. Temperature (both high and low) and lowered moisture had a greater inhibiting effect on NO₂-N oxidizers than on NH₄-N oxidizers.

There was a decrease in the total inorganic N recovered when unfavorable nitrification conditions were encountered. This loss of inorganic N was apparently from the NH₄-N pool.

¹ Contribution from the Agronomy Department, Utah State Agr. Exp. Sta., Logan, and approved by the Director as Journal Paper No. 150. Presented before Div. III, Soil Science Society of America, Dec. 5, 1960, at Chicago, Ill. This work was supported in part by funds from Regional Research, W-31.

² Formerly Graduate Assistant, now Associate Professor, Abilene Christian College, Abilene, Tex., and Associate Professor of Agronomy, respectively.

Received for publication July 6, 1961. Accepted for publication July 14, 1961.