Effects Of Nitrogen Reduction Combined With Biochar Application On Soil Organic Carbon Stability And Rice Yield

Nitrogen reduction combined with biochar application is of great significance for increasing rice yield,reducing CO₂emissions,increasing carbon sink capacity of rice fields and mitigating climate warming.In order to solve the effects of excessive application of nitrogen fertilizer on environment,rice yield and high efficiency use of nitrogen fertilizer.In this study,five nitrogenous fertilizer application gradients（T0～T4）were set based on field experiments:100%,90%,80%,70%and 60%fertilizer N were divided into groups of soil organic carbon based on the principle of iso-nitrogen,using iso-nitrogen biochar instead of nitrogen reduction,taking no fertilization as control（CK）,combined with indoor mineralization culture and Stewart’s soil physical-chemical grouping method.To reveal the effects of nitrogen reduction combined with biochar application on organic carbon composition,mineralization and rice yield in paddy fields.The results show that:（1）All fertilization treatments increased soil organic carbon（SOC）content,and nitrogen reduction combined with biochar treatment was inversely proportional to nitrogen reduction.Compared with T0 treatment,nitrogen reduction combined with biochar treatment increased soil free activity,physical protection and biochemical protection organic carbon content by 5.49%～23.40%,4.42%～51.02%and 43.86%～107.02%,respectively.However,only T3 and T4 treatments increased the content of soil organic carbon by 8.94%and 27.41%.The proportion of biochemically protected organic carbon（SOC）in T3 treatment was significantly increased by20.11%-54.33%,while the proportion of free organic carbon（SOC）in T3 treatment was significantly decreased by 21.64%,while the proportion of chemically protected organic carbon（SOC）was significantly increased by 29.59%.（2）The SOC mineralization rate was divided into three stages during the culture period.After the culture,the cumulative SOC mineralization amount and cumulative SOC mineralization rate fluctuated between 1.39～1.75 g/kg and 6.02%～8.43%,respectively,and T3 treatment was the lowest.（3）T3 treatment had a better effect on soil nutrients,catalase,urease and sucrase activities;Compared with T0 treatment,rice yield,nitrogen partial productivity,nitrogen agronomic efficiency and nitrogen apparent use efficiency were significantly increased by 24.63%,24.54%,149.29%and 46.21%respectively in T3 treatment.Correlation analysis showed that rice yield was negatively correlated with soil organic carbon mineralization rate.In conclusion,70%fertilizer N combined with biochar application can significantly increase soil nutrient content,increase soil chemical protection and biochemical protection organic carbon content and proportion,reduce SOC mineralization,promote soil carbon fixation,improve soil enzyme activity,promote rice yield and nitrogen absorption.