Mihoko Moriizumi

Changes in the N Recovery Process from 15N-Labeled Swine Manure Compost and Rice Bran in Direct-Seeded Rice by Simultaneous Application of Cattle Manure Compost

The N recovery from 15N-labeled swine manure compost and rice bran with or without simultaneous application of unlabeled cattle manure compost was examined in a paddy field with direct-seeded rice during a 1-year period (1 crop season). In all the 15N-labeled materials including (15NH4)2SO4, the processes of N recovery from the 15N materials by rice plants were different between the plots with and without application of cattle manure compost. At the tillering stage, the N recovery rates from the 15N materials in the plots with application of cattle manure compost were significantly lower than those in the plots without application of cattle manure compost. These recovery rates, however, became close and no significant differences were observed at the maturity stage. Thus, simultaneous application of cattle manure compost could impede the N recovery from swine manure compost, rice bran as well as (NH4)2SO4.

Molecular weight separation of hot-water extractable soil organic matter using high-performance size exclusion chromatography with chemiluminescent nitrogen detection

To characterize soil organic nitrogen (N), we applied high-performance size exclusion chromatography (HPSEC) and chemiluminescent nitrogen detection (CLND) to the molecular weight separation of hot-water extractable organic matter (HWEOM) from soils that had been amended with or without plant residue compost applied at a rate of 2 kg m−2 y−1 for 25 years. The N chromatogram of the HWEOM showed that the HWEOM containing N had molecular weights ranging from 0.1 to 100 kDa. The N chromatograms of HWEOM from soils without compost differed among four soils (Cumulic Andosol, Low-humic Andosol, Gray Lowland soil, and Yellow soil). The N intensities in the HWEOM chromatograms were larger in the soils with compost amended than in those without compost over the whole range of molecular weights. These results demonstrate that HPSEC/CLND is a useful tool to investigate the structure and dynamics of water soluble organic N in soil.

Demonstration of discrepancy in N remaining rate of organic matter evaluated by N content and 15N content in the glass fiber-filter paper bag method

Abstract 15N-labeled rice straw, wheat straw, and cattle manure sawdust compost were used to evaluate the N remaining rate of organic matter by the application of the glass fiber-filter paper bag method, and to demonstrate the discrepancy between the N remaining rate of organic matter evaluated by the N content and the N remaining rate of organic matter directly evaluated by the 15N content. In all three kinds of organic matters examined, a discrepancy in the N remaining rate of organic matter was observed between the evaluation by the N content and the evaluation by the 15N content. Loss of N from organic matter was observed using the 15N content, though the N remaining rates of wheat straw and rice straw evaluated by the N content were above 100% throughout the experimental period. The N inflow into and N outflow from the glass fiber-filter paper bag occurred simultaneously. The discrepancy between the N remaining rate of organic matter evaluated by the N content and the N remaining rate of organic matter evaluated by the 15N content became larger as the C / N ratio of organic matter increased.