Ammonium-form fertilizers have special significance in the production of the California rice crop because ammonium nitrogen is the only inorganic form that can be maintained in continuously flooded soils. However, the maintenance of ammonium nitrogen is dependent upon proper fertilizer placement. When ammonium nitrogen is placed at a depth of 2?-4? in a rice seedbed prior to flooding, its maximum utilization for increased rice yields is realized. Nitrogen which is converted to nitrate nitrogen before or after flooding will be denitrified and lost from the soil as nitrogen gas.