Nitrogen Transport and Change in Amount of ATP with Nitrification in Andisol during Evaporation

Abstract

The decrease in ammonia nitrogen (NH₄-N) and increase in nitrate nitrogen (NO₃-N) in batch tests of Iwate Andosol at a range of saturations were fitted with a first-order transformation equation. The first-order rate constant (µ) of nitrification decreased with decreasing soil water content. Simultaneously, column evaporation experiments were performed to investigate redistribution of NH₄-N and NO₃-N in the Andosol with nitrification and soil water flow. Most of the NH₄-N in the column was depleted by nitrification, and the produced NO₃-N was accumulated near the surface with the soil water flow. The rate of NH₄-N decrease was higher in the early stages of evaporation, during which the soil contained higher amounts of water. Then, the results of column evaporation experiments were analyzed using µ obtained from the batch tests. When µ was given as a function of water content, instead of a constant value, the calculation more closely reproduced the experimental results, especially for early stages of evaporation. The amount of ATP in the soil was also measured for the batch tests and evaporation experiments to provide an index for soil microbial activity. Larger amounts of ATP were observed in soils with larger µ. This suggests that the first-order rate constant may be estimated from the amount of ATP, which is relatively easy to measure.