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The Effects of Soil Properties on Nitrification and Nitrification Inhibition¹

ABSTRACT

An understanding of the impact of the soil environment on nitrification in the presence and absence of a nitrification inhibitor is important to proper use of this group of compounds. The objective of this study was to describe the kinetics of the nitrification process and define how a nitrification inhibitor, etradiazole (5-ethoxy-3-trichloromethyl-1,2,4-thiadiazole), altered the reaction. Nitrification was found to obey zero-order kinetics with the rate constant being a function of temperature, moisture, and pH. The absolute zero-order rate was also a function of initial ammonium concentration. As temperature increased over the range of 16 to 28°C, the rate constant increased according to the Arrhenius equation. The relative influence of the inhibitor on the rate constant decreased with temperature increases. Below the optimum soil moisture for nitrification a linear decline in rate was observed as soil moisture decreased over the range of 0.20 to 0.12 g g^–1 (–40 to – 140 kPa). This decline was greater in the control than in the soil amended with etradiazole. Nitrification linearly increased with soil pH over the range of 4.9 to 7.2. Using the above relationships, the rate of nitrification was predictable for an independent group of 19 soils. This same group of soils was evaluated for inhibition at two etradiazole rates at optimum moisture and 14°C. Inhibition decreased as organic carbon content increased above 13 g kg^–1 with the extent of the decrease being modified by the amount of clay in the soil. As inhibitor rate increased, inhibition was enhanced by a constant amount, suggesting that the relationships described above remained in effect.

¹ Published with the approval of the Director of the Univ. of Arkansas Agricultural Experiment Station.

² Professor of agronomy, Univ. of Arkansas, Fayetteville, AR 72701.

Received for publication March 2, 1984. Accepted for publication June 13, 1984.