Effects of the depth of NO and N2O productions in soil on their emission rates to the atmosphere:: analysis by a simulation model

Many factors are concerned in the changing forms of nitrogen compounds in soil, so it is not easy to make precise models to simulate the concentration profiles of soil nitric oxide (NO) and nitrous oxide (N2O) and their emission rates under various soil conditions. We prepared a simple mathematical simulation model based on soil concentration profiles of NO and N2O. The profiles were measured at lysimeters filled with Andosol soil and fertilized with ammonium sulfate at rate of 200 kgNha(-1), incorporating to plow layer (Hirose & Tsuruta, 1996). In this model, diffusion of gases in soil followed Fick's law and the diffusion coefficient was adopted from Sallam et al. (1984). The gas production rate was set up at constant value in the site of gas production, and the gaseous consumption followed Michaelis-Menten kinetics. By changing only the depth of NO and N2O production in soil in this model, we obtained the following results. (1) When the depth of gas production was set at near the soil surface (NO: 0-10 cm, N2O: 0-8 cm), the emission rates of both gases corresponded with the results of the lysimeter-measurement. (2) When the depth of gas production was shifted down 10 cm deeper (NO: 10-20 cm, N2O: 10-18 cm), the gas emission rate of NO decreased to 1.3% of (1), while that of N2O was almost the same as (1). (3) In the case that the total intensity of produced gases was not changed from (1) or (2), but that the extent of gas productions expanded 3 times wider (NO: 0-30 cm, N2O: 0-24 cm) than (1) or (2), the emission rates of NO and N2O became 26% and 95% of (1), respectively. The above results suggest the possibility of mitigating NO emission by setting the site of gaseous production in deeper soil, e.g. by means of deep application of fertilizer.