The Influence of Organic Amendment Source on Carbon and Nitrogen Mineralization in Different Soils

Abstract

Soil organic matter is one of the largest stores of carbon and nitrogen in various ecosystems that can crucially improve plant nutrition. The present study was conducted to investigate the effect of organic matter sources on carbon and nitrogen mineralization and also the contemporary comparison of carbon and nitrogen mineralization and nitrogen immobilization in soils amended with different organic treatments. Accordingly, six types of organic amendments were applied to three types of soils, under a constant temperature and moisture at the laboratory scale. The treated soils were incubated 60 and 120 days for nitrogen and carbon mineralization study, respectively. Results showed two decomposition stages, an initial rapid increase in decomposition in the first 20 days followed by a slower stage reaching a steady state condition. The amount of mineralized carbon ranged from 980 to 6860 mg/kg of dry soil for soils incorporating with different types of organic matters. The carbon mineralization kinetic data was well fitted to a second-order kinetic model showing the differences in microbial decomposition resistance of residues contents. The kinetic of carbon and nitrogen mineralization fluctuated similarly but in different scales. Net ammonification of fertilizer group, sheep manure, cow manure, and vermicompost was decreased, whereas in plant residue group, plane tree leaves, corn leaves, and wheat straw was increased. Two nitrification periods (first 10 days and 35 to 60 days) and an immobilization period (10 to 35 days) were observed. After 60 days of incubation of amended clayey soil, the nitrification values in plane tree leaves, corn leaves, wheat straw, municipal waste vermicompost, cow manure, and sheep manure were − 13.98, 14.06, 13.22, 34.88, − 12.25, and − 12.15 mg kg−1, respectively. The carbon and nitrogen mineralization trends fluctuated due to probably different resistance of substance components to microbial decomposition. Since the nitrate is the main part of inorganic N, therefore, net N mineralization had a similar trend as nitrification in different soils. Those organic residues with high ratios of C/N immobilized the mineral nitrogen, due to the presence of more carbon and a higher nitrogen decomposition rate, resulting in suppressed levels of nitrogen in the amended soil.