Effects of soil solution on the dynamics of N2O emissions:: a review

In this review, which consists of two parts, major interactions between nitrous oxide (N2O) and soil solution are described. In the first part, as an introduction, concentrations of dissolved N2O in different aqueous systems are summarized. An inventory of data on maximal N2O concentrations in soil solution (up to 9984 mu g N2O-N l(-1)) and in soil air (up to 8300 ppm) from literature is presented. The peak N2O concentrations represent a N2O supersaturation in the soil solution up to 30000 times with respect to ambient air and a soil air N2O concentration about 25000 times higher than in the atmosphere. The main physico-chemical parameters (solubility, diffusion) controlling N2O distribution between soil solution and soil air are outlined. The influences of cultivation practice, nitrogen turnover, water content and temperature on N2O accumulation in soil solution and soil air are reviewed. In the second part some models of N2O dynamics in soils are discussed with emphasis on N2O transport processes. A simple qualitative scheme is developed to categorize the effects of the soil solution on N2O dynamics in soils. In this scheme the temporary, intensive N2O oversaturation of the soil solution is interpreted as a result of gas diffusion inhibition by water (barrier function of soil solution) resulting in an accumulation of N2O. In addition, N2O supersaturation is an indication that transitory much N2O can be stored in the soil solution (storage function of soil solution). Where the soil solution flows up-, down- or sidewards it can act as a relevant transport medium for dissolved N2O (transport function of soil solution). This scheme is applied to examples from the literature.