Improving salt leaching in a simulated saline soil column by three biochars derived from rice straw (Oryza sativa L.), sunflower straw (Helianthus annuus), and cow manure

There is little knowledge about whether biochar amendment can reduce soil salinity, though increasing data have shown that biochar amendment can improve soil fertility and crop production. In this study, we hypothesized that biochar amendment could promote salt leaching, and the effect might depend on biochar properties. The aims were to evaluate the impacts of three biochars on promoting salt washing and then find possible biochars as saline soil conditioner. Three biochars derived from rice (Oryza sativa L.) straw (RSB), sunflower (Helianthus annuus) straw (SSB), and cow manure (CMB) through a slow pyrolysis process were respectively added at a rate of 5% (w/w) into 0 to 35 cm (0 to 13.8 in) soil depth of a sulfate (SO42-) saline soil column. After washing with deionized water, the eluent was collected from each column and then measured for electrical conductivity (EC) and major salt ions. At the end of washing, the major salt ions were determined in each soil layer. Results showed that the biochar-amended columns discharged efflux 24 to 40 days earlier than that of the control without biochar (CK). Biochar addition saved 56 to 62 days for the EC values of the efflux to be reduced to 5 dS m(-1). Among the three biochars, SSB led to much lower contents of the most detrimental ions of both sodium (Na+) and bicarbonate (HCO3-) in the soil at the end of experiment, showing that SSB may be a highly potential amendment of saline soils in the Hetao region in China. Further work is required for investigating and confirming the effect of biochar amendment on different saline soils with different textures, salinities, and alkalinities in both lab and field, together with local irrigation water, and then quantifying water saving and crop production through biochar amendment in agriculture.