Nitrogen Mineralization in a Semiarid Silt Loam Soil in the Pacific Northwest.

The mineralization of nitrogen from soil organic matter or plant residues can provide a substantial amount of nitrogen for crop growth.  Microbial activity in a soil may be adversely affected by either very high or low soil water content.  A field study was conducted to determine the affect of three moisture regimes on nitrogen mineralization at soil depths to 100 cm.  Soil samples were taken from the field over a six-month period during the growing season and analyzed for total nitrogen, total carbon, nitrate-nitrogen and ammonium-nitrogen.  Soil temperature and moisture were also determined.  Recorded soil temperature showed a diurnal curve with daily fluctuations of 12°C in August.  Net nitrogen mineralization generally increased with time at all depths measured; however, nitrogen mineralization decreased with increasing soil depth.  Nitrogen mineralization slightly increased with increasing soil moisture under similar conditions of soil carbon concentration.  However, nitrogen mineralization was directly proportional to soil carbon concentrations.  Considerable amounts of N were mineralized in soil layers below the top 15 cm of sandy loam soil, cropped in proceeding years with winter wheat in a summer fallow rotation.