Microclimatic controls of nitrogen mineralization and nitrification in shortgrass steppe soils

The depth distributions of rates of net nitrogen mineralization and nitrification were measured in a series of field and laboratory incubations. Field studies suggested that the highest rates of mineralization and nitrification occurred in the surface 2.5 cm such that forty to sixty percent of the N mineralization in 20-cm soil column occurred in the surface 2.5cm. Some upward nitrate movement occurred but laboratory studies suggested that surface rates were not an artifact of nitrate mobility alone. Microclimatic data indicate that either dew or upward movement and condensation of soil water vapor may drive biological activity at the soil surface. High rates of N mineralization even in dry horizons were sustained as long as water was stored within the 0-to 20-cm depth. High rates of nitrification were found in all incubations, and field measurements showed NO 3 − to be the predominant form of inorganic N, despite previous characterization of the shortgrass steppe as an NH 4 + -dominated system.