Nitrogen Distribution in Rice Straw and Rice Hulls Treated with Sodium Chlorite and Ammonia

Abstract

Rice straw (RS) and rice hulls (RH) were mixed with 50% water of air dry matter and then simultaneously treated with 0, 5 or 25% sodium chlorite (NaClO2, by wt.) and 5% ammonia (NH3, by wt.) containing 10.4 atom % 15N for 3 days at 45°C. All samples were subjected to the determination of the fractionation of nitrogen and the distribution of 15N in each nitrogen fraction. Ammonia nitrogen (AN) and amide nitrogen (AmN) contents of original materials were very low and hot water insoluble nitrogen (ISN) was accounted for most of total N in original samples. The rate of total retained N to added ammonia in the ammoniated materials treated with 0.5 and 25% of NaClO2 was 33.3, 41.5 and 54.7% for RS and 26.4, 36.4 and 42.5% for RH, respectively. The nitrogen recovered as AN and AmN was markedly increased with the increasing level of NaClO2, and the sum of these values showed about two-thirds of total retained nitrogen. ISN content was also increased by these treatments and about 5.3 and 6.2% of the added ammonia were recovered as ISN in treated RS and RH, respectively. The retained total N, AN and AmN derived from added ammonia were accounted for about 100% of total increased N, indicating that most of the increased N in these fractions were originated from added ammonia. The retained ISN derived from added ammonia was less than total increased ISN in RS and RH treated with 0 and 5% NaClO2, but the values of samples treated with 25% NaClO2 were accounted for 138 and 135%, respectively. These results showed that the ISN in the original materials would be affected by the treatments.