Hydrolyzable Organic Forms of Nitrogen in some Rice Soil Profiles as Affected by Organic Matter Application

Abstract

The influence of previous application of organic matter for a period of 16 years on the amounts and distribution of organic N was investigated using profile samples from four rice field plots. This study was conducted by determining soil horizon samples for nonhydrolyzable Nand hydrolyzable (total, ammonium, amino sugar, and unidentified) N with the hot 6 N HCl hydrolysis procedure. Organic matter treatments, including the application of rice compost, rice straw, and Italian ryegrass residues, led to a marked increase in all forms of soil N whose content was highest in the surface soil and decreased down the profile. The proportion of hydrolyzable N (40-81%) to the total N decreased with depth and that of nonhydrolyzable N (19-60%) increased with depth. Furthermore, the proportion of amino acid N (4-28%), amino sugar N (2-5%), and unidentified N (12-32%) decreased with depth, whereas that of hydrolyzable ammonium N (16-24%) remained fairly constant throughout the profile. In general, the profile distribution pattern indicated no differences regarding the proportion of each organic N fraction, so that organic matter application appeared to have little effect on these parameters. In spite of the considerable differences observed in the amino acid content, the amino acid composition of all horizon samples in the profile was remarkably similar independently of the depth as well as the treatments. Neutral amino acids were present in very large amounts followed by acidic and basic amino acids with a rough ratio of 6.5 : 2.5 : 1.0. Moreover, the amino acid compositional pattern in the soil was closely consistent with that obtained from the organic residues used for soil application. In the linear correlation analysis, mineralizable N derived from anaerobic incubation method was found to be significantly correlated with all the N fractions including even nonhydrolyzable N. Stepwise regression analysis indicated, however, that there were no differences in terms of the relative contribution from each soil N fraction. Presumably, the degradation of the soil N compounds by the chemical treatment resulted in a pattern not closely related to the biological mineralization of soil N.

Biogeochemistry of paddy soils

“…The concentration of amino acid-N strongly correlated with the mineralizable N under waterlogged conditions (Mohapatra and Khan, 1983), and concentrations of hydrolysable amino acids were higher in the surface than in the subsurface soil and dominated by neutral structures (Gotoh et al, 1986). Small proteins and free amino acids can apparently even be taken up actively by (upland) rice plants (Yanamuro et al, 1999;Yamagata, 2000).…”

Bacterial Communities Responsible for the Decomposition of Rice Straw Compost in a Japanese Rice Paddy Field Estimated by DGGE Analysis of Amplified 16S rDNA and 16S rRNA Fragments

“…The application of rice straw compost to paddy fields has been investigated extensively in terms of its effects on soil nitrogen fertility, soil organic matter content and growth of rice (e.g. Maeda and Shiga 1978;Gotoh et al 1984Gotoh et al , 1986Inoko 1984;Shiota et al 1984;Shiga et al 1985a, b). Its effects on soil microorganisms have also been well documented.…”

Microbial communities responsible for the decomposition of rice straw compost in a Japanese rice paddy field determined by phospholipid fatty acid (PLFA) analysis

“…Application of rice straw compost to rice fields has been investigated extensively from the viewpoint of its influences on soil fertility, especially nitrogen fertility, content of soil organic matter, and growth of rice (e.g. Maeda and Shiga 1978;Gotoh et al 1984Gotoh et al , 1986Inoko 1984;Shiota et al 1984;Shiga et al 1985a, b). Its effects on microorganisms in soil have also been well documented and microbial numbers, amount of biomass and activities generally increased by the application of rice straw compost (e.g.…”