EFFECT OF WHEAT STRAW INCORPORATION ON DENITRIFICATION OF N UNDER ANAEROBIC AND AEROBIC CONDITIONS

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Abstract
The effects of wheat straw incorporation on denitrification, immobilization of N, and C mineralization were investigated at H2O contents of 60, 90 and 120% saturation. Incorporation of increasing levels of straw consistently increased the rate of denitrification for the first 4-8 d, followed by negligible N losses thereafter. In a total period of 96 d, the addition of 1.0% straw increased N losses from 2.5 to 10.1, and from 61.6 to 83.9 .mu.g g-1 in the 60 and 120% water saturation treatments, respectively. The pattern of CO2-C evolved was practically identical to that of the denitrification rate for the initial period when sufficient NO3- was present. This study has confirmed that in flooded soils, high rates of denitrification will persist only when C is supplied by native or applied organic C sources, provided adequate NO3- is present. When NO3- was low, denitrification rates rapidly decreased, even with a sufficient supply of C. Immobilization of fertilizer N (50 .mu.g N g-1 as K15NO3) was very rapid. Around 90% of the total immobilization of applied N occurred within 4 d. Incorporation of 1.0% straw increased the immobilization of fertilizer N from 8.4 to 42.8, and from 1.0 to 7.6% in the 60 and 120% water-saturated treatments, respectively. Remineralization of recently immobilized fertilizer N was observed after 32 d in the 60% saturation treatments only.