Biochar co-applied with organic amendments increased soil-plant potassium and root biomass but not crop yield

Purpose: Biochar can improve soil nutrient retention and alleviate salinity; however, use is not widespread due to cost. Biochar is usually co-applied with a full-rate of supplementary fertiliser before planting. This study investigated co-application of bamboo biochar with organic fertiliser and amendments on nutrient cycling, plant growth, yield and commercial value of ginger. Methods: Four treatments were applied including no amendment, organic amendments and organic amendments co-applied with biochar at two applications rates of 10 t ha⁻¹ and 30 t ha⁻¹. Plant growth, biomass, foliar nutrient and water-extractable soil nutrients were examined. Results: Co-applied high rate biochar increased available soil potassium (K) concentration (+ 89%) over 22 weeks and led to increased foliar K concentration (+ 25%) at harvest and after 30 weeks compared with organic amendments alone. Biochar high rate decreased soil sodium concentration (− 22%) over 22 weeks. Biochar high rate increased root mass fraction and plant height but decreased the number of stems, and therefore, did not increase aboveground biomass compared with all other treatments. In contrast, ginger rhizome yield, grade and commercial value were not affected by biochar treatments. Conclusion: Added biochar provided additional net K that improved foliar concentration late in the growing season following dissolution. The additional K supply then stimulated root growth and biomass re-allocation despite daily irrigation throughout the growing season. Therefore, we suggest biochar as a useful amendment to prevent nutrient loss and alleviate salinity for organic crops.