The roles of co-composted biochar (COMBI) in improving soil . Jan 1, 2021 · Biochar and biochar-compost mixture can improve soil fertility and crop yields by supplying nutrients, increasing soil pH, CEC, nutrient use efficiency (NUE), and nutrient uptake at certain application rate, and also by improving soil WHC especially in sandy soils, and drainage in clayey soils (Agegnehu et al., 2016a