INTRODUCTION Nitrogen is a key component of soil organic matter. Only when we have succeeded in characterizing the major part of organic N-containing compounds will we be able to understand fully the transformation re...INTRODUCTION Nitrogen is a key component of soil organic matter. Only when we have succeeded in characterizing the major part of organic N-containing compounds will we be able to understand fully the transformation reactions in the soil and to use soil-N more efficiently. However, only about 1/ 4——1/ 2 of the total N in humic acid (HA), one of the major constituents of soil organic matter, can be accounted for as amino acids and amino sugars, and most of the remainder has still to be accounted for. It has been展开更多
Results of a 10-year decomposition experiment indicated that the annual mineralization rate of organic N in newly-formed humus varied with the type of original plant materials and the water regimes for decomposition, ...Results of a 10-year decomposition experiment indicated that the annual mineralization rate of organic N in newly-formed humus varied with the type of original plant materials and the water regimes for decomposition, ranging from 0.028 to 0.074. The mineralization rate under waterlogged conditions was higher than that under upland conditions. The proportion of α-amino acid N in humus newly-formed under waterlogged conditions was slightly higher than that under upland conditions. It decreased gradually with time, while the proportion of nonhydrolyzable N showed no consistent trend, irrespective of the water regimes for decomposition. The distribution of amino acids in humus newly- formed from different plant materials under various water regimes was quite similar with that in original plant materials, and only minor differences could be found among them. For example, in comparison to original plant materials, the newly-formed humus contained higher proportions of isoleucine, cystine, γ-amino-butync acid and ornithine, and lower proportions of phenylalanine and proline. Moreover the proportion of phenylalanine was higher in the humus newly-formed under waterlogged conditions than that under upland conditions.展开更多
In the present paper, the composition of humus and the charateHstics of humic acid from seven paddy soils were compared with those of upland (and / or natural) soils. Results show that :(1) in each group of the soil s...In the present paper, the composition of humus and the charateHstics of humic acid from seven paddy soils were compared with those of upland (and / or natural) soils. Results show that :(1) in each group of the soil samples for comparison the HA / FA ratio of the humus of a paddy soil, in most cases, was appreciably higher than that of adjacent upland (and / or natural) soil derived from the same parent material; (2) the humic acid extracted from the paddy soils was characterized by a higher C/ O ratio, a higher content of methoxyl groups, and a lower content of carboxyl groups than those from the corresponding upland (and / or natural) flooded soils, implying that the humic acid formed under rice cultivation is in a lower degree of humification than that formed under upland (and / or natural) conditions; and (3) the humic acid of paddy soils, however, was not always characterized by a lower aromaticity than that of the corresponding upland (and / or natural) soils.展开更多
基金Project supported by the National Natural Science Foundation of China.
文摘INTRODUCTION Nitrogen is a key component of soil organic matter. Only when we have succeeded in characterizing the major part of organic N-containing compounds will we be able to understand fully the transformation reactions in the soil and to use soil-N more efficiently. However, only about 1/ 4——1/ 2 of the total N in humic acid (HA), one of the major constituents of soil organic matter, can be accounted for as amino acids and amino sugars, and most of the remainder has still to be accounted for. It has been
基金Project supported by the National Natural Science Foundation of China.
文摘Results of a 10-year decomposition experiment indicated that the annual mineralization rate of organic N in newly-formed humus varied with the type of original plant materials and the water regimes for decomposition, ranging from 0.028 to 0.074. The mineralization rate under waterlogged conditions was higher than that under upland conditions. The proportion of α-amino acid N in humus newly-formed under waterlogged conditions was slightly higher than that under upland conditions. It decreased gradually with time, while the proportion of nonhydrolyzable N showed no consistent trend, irrespective of the water regimes for decomposition. The distribution of amino acids in humus newly- formed from different plant materials under various water regimes was quite similar with that in original plant materials, and only minor differences could be found among them. For example, in comparison to original plant materials, the newly-formed humus contained higher proportions of isoleucine, cystine, γ-amino-butync acid and ornithine, and lower proportions of phenylalanine and proline. Moreover the proportion of phenylalanine was higher in the humus newly-formed under waterlogged conditions than that under upland conditions.
文摘In the present paper, the composition of humus and the charateHstics of humic acid from seven paddy soils were compared with those of upland (and / or natural) soils. Results show that :(1) in each group of the soil samples for comparison the HA / FA ratio of the humus of a paddy soil, in most cases, was appreciably higher than that of adjacent upland (and / or natural) soil derived from the same parent material; (2) the humic acid extracted from the paddy soils was characterized by a higher C/ O ratio, a higher content of methoxyl groups, and a lower content of carboxyl groups than those from the corresponding upland (and / or natural) flooded soils, implying that the humic acid formed under rice cultivation is in a lower degree of humification than that formed under upland (and / or natural) conditions; and (3) the humic acid of paddy soils, however, was not always characterized by a lower aromaticity than that of the corresponding upland (and / or natural) soils.