Applying Biochar Mineral Complex to Minimise Nutrient Leaching and Increase Economic Benefits

Biochar mineral complex (BMC) can improve nutrient use efficiency (NUE) and reduce nutrient leaching, but the optimal application form and rate of application in soilless cropping systems remain unclear. This study evaluated co-applying BMC, either in solid form and placed to form a horizontal laminar layer approximately halfway up the potting media column, or as a liquid BMC suspension combined with reduced fertiliser rates in a protected ginger cropping system using pine bark potting media. Six treatments were examined: full-rate (15 t ha−1) and half-rate (7.5 t ha−1) organic fertiliser blend, BMC at high-rate (1 t ha−1) and low-rate (0.5 t ha−1) co-applied with half-rate fertiliser, BMC at high-rate without fertiliser, and BMC suspension at high-rate co-applied with half-rate fertiliser. Aboveground biomass, rhizome yield, nitrogen (N) and phosphorus (P) leaching, NUE, and net income were assessed. Fertiliser costs were reduced by 28% to 30% by applying half-rate fertiliser with or without BMC, respectively, and without decreasing rhizome yield, aboveground biomass, and NUE, compared to applying full-rate fertiliser. Co-applying solid BMC as a layer and at a low rate with half-rate fertiliser reduced N and P leaching without affecting yield or profitability. The BMC suspension showed no significant difference from full-rate fertiliser in yield and leaching outcomes while offering advantages for mechanised application in labour-intensive cropping systems. Overall, co-applying BMC either as a solid layer or as a liquid suspension with reduced fertiliser rates offers an economically and environmentally sustainable alternative to conventional fertiliser use in soilless cropping systems.