Effect of moisture level on nitrogen immobilization as affected by wheat straw decomposition in soil

Samples of a slightly degraded chernozem soil were amended with 2 per cent of wheat straw at three moisture levels (10, 20, and 30 per cent) and were provided with 160, 240, and 400 ppm of ammoniacal nitrogen. Amounts of total, ammonia, and nitrate were determined at different periods of incubation at 28 degrees C and immobilization of the total available nitrogen in the soil was calculated. Substantial amounts of the added nitrogen were immobilized in the soil as a result of the straw decomposition during the first month of incubation. The amount of inorganic nitrogen (NH4 + -N + NO3 - -N), bound within 75 days of incubation, was almost three times less than that immobilized within 30 days. Maximum quantity of nitrogen was immobilized at 30 and 20 per cent moisture levels at 30 and 75 days of incubation, respectively. Minimum immobilization was observed at 10 per cent moisture at almost all levels of nitrogen. The absolute amount of nitrogen immobilized increased in proportion to the quantity of nitrogen added, but the relative immobilization tended to decrease with the increased inorganic nitrogen the soil.