Effects of nitrogen fertilizer application and straw returning on stable organic carbon of cinnamon soil
In this study,the effects of nitrogen(N)fertilization and straw returning on the content,fractions and stability of soil total organic carbon(TOC)were investigated.Soil samples were taken from Fuxin Agricultural Environment and Farmland Conservation Scientific Observatory Experimental Station in Liaoning Province,China,where the treatments were continuously maintained for eight years.The soil samples were analyzed using methods such as acid-base extraction,density separation,metal hydroxide extraction,14C dating,and chemical oxidation.The results showed that,in comparison with the control,apply only N fertilization(N1)decreased TOC content by 5.5%,whereas N fertilization in combination with straw returning(NS)increased TOC content by 2.8%.In both the N1 and NS treatment,the carbon and nitrogen ratio was higher than that of the control.Upon N1 and NS,the fraction of acid-base extractable soil organic carbon(SOC)decreased,in which the fraction of humic acid(HA)decreased from 63.6%to 49.5%.Correspondingly,the acid-base non-extractable humin fraction increased by 25.9%-39.0%.There was no significant difference in the proportion of the light and heavy fraction of SOC between treatments.The heavy fraction was dominant,accounting for 62.3%±0.4%of TOC.The ratios of extractable C to Fe and Al was very low,indicating that,besides oxides bound to Fe and Al,most SOC in the heavy fraction was associated with clay as coagulates and coating.14C dating showed that the average age of TOC in these soils was around 2 000 years old.Overall,the long-term stable SOC dominated in these soils.Due to the addition of new organic carbon,the application of N and straw increased the mineral-associated humin-like SOC.However,because of the priming effect,a fraction of original stable SOC was decomposed,leading to a decrease of fulvic acid-like SOC.The instability of newly added organic carbon and the degradation of stable SOC stimulated by the priming effect limited the contribution of N1 and NS to TOC accumulation.
万方数据
维普
