Effects of Continuous Biochar Application on Rapeseed Yield and Spectral Characteristics of Dissolved Organic Carbon in Upland Red Soil

  Objective  The paper aims to make sure the effects of continuous biochar application on dissolved organic carbon (DOC) in upland red soil.

  Method  The soil physicochemical properties, rapeseed yield, DOC fluorescence spectrum components, and parameters were detected after 7 years of low-dose (750-1500 kg hm⁻²) biochar application.

  Result  Biochar application reduced soil exchange Al³⁺ (0.69-0.87 cmol kg⁻¹), but decreased the soil pH (0.13-0.21), organic matter (11.7%-18.1%), and soluble carbon contents (127.5%-127.8%) compared with control. The pods’ number and the yield were increased 39.8%-45.1% and 3.5%-20.3%, respectively. And the trend was increased with the amount of biochar application. Continuous biochar application increased the proportion of tyrosine and fulvic acid-like in DOC, but reduced the proportion of microbial metabolites. Biochar application decreased fluorescence index (4.4%-10.6%), freshness index (17.4%-18.4%) and biogenic index 0.26 (22.6%), and increased the humification index (1.2%-5.1%) in soil DOC. Correlation analysis indicated that soil DOC was positively correlated with soil pH, and negatively correlated with exchange Al³⁺. Microbial metabolites were negatively correlated with pH, and positively correlated with exchange Al³⁺. Soil tyrosine was negatively correlated with exchange Al³⁺. Redundancy analysis showed that soil pH and exchangeable H⁺ were the main indicators affecting the changes of soil DOC and its spectral characteristics.

  Conclusion  Continuous low-volume biochar application in red soil dryland can increase rapeseed yield, improve the acidity of red soil, increase DOC content, fulvic acid-like substances, and humification coefficient to improve stability in DOC soil.