The soluble fraction from straw-derived biochar supplies nutrients and affects carbon storage of coastal mudflat soil in rice paddy.

Incorporation of biochar into soil has been proposed as a strategy for enhancing soil fertility and rice production. A pot trial was carried out to investigate the effects of the dissolvable fraction of biochar in the Yangtze River estuary, China. Soil in plastic pots was incorporated with straw biochar at five different rates: 0%, 5%, 10%, 15%, and 20% (w/wet weight). The rice height, tiller number, and grain yield were recorded; soils and surface water were sampled, and key chemical properties were investigated. Rice grain yield was improved by 29.1-34.2%, and the grain-to-straw ratio was promoted by 8.0-26.1% in the treatments with 10-15% biochar incorporated compared with the control. Soil total organic carbon and total nitrogen contents increased 65.7-242.8% and 22.9-75.3% in the biochar-amended treatments, respectively. Meanwhile, the soil dissolved organic carbon contents increased by 13.4-25.3% in biochar-amended treatments. Higher amounts of added biochar resulted in increased soil electrical conductivity but had no significant effect on soil pH. The major anion was Cl, and the main cations were K and Na in the mudflat soil. Addition of 10-15% straw biochar to soil for agronomic purposes is a potentially sustainable ecologically technology.