Distinct forms of liquid biochar mineral complex fertilisers differently increase crop yield, nutrient balance and economic return

Abstract Sustaining crop yield is a growing challenge due to soil fertility loss and climate change. As a result, fertiliser application is increasing to sustain yield and counteract low fertiliser use efficiency. Developing nutrient-efficient fertilisers, for example by combining biochar with fertilisers, is thus crucially needed. In this context, the development of biochar-mineral complex (BMC) fertilisers into liquefied products suitable for broadacre application is highly innovative. This study aimed to explore the agronomic benefits and economic viability of four novel liquefied BMCs designed for application within a pasture cropping system. The different forms of developed BMCs included two non-enriched BMCs (BMC1 and BMC2) that were micronised using different techniques, a phosphorus (P)-enriched BMC (BMC3), and a nitrogen (N)-enriched BMC (BMC4), all applied both with- and without co-fertilisation. Soil biochemistry, plant NP uptake, NP balances, plant yield and cost–benefit were examined. Pasture yield was significantly higher using BMC1 and BMC3 with co-fertilisation than without, most likely due to improved P availability, as evidenced by positive P balances. Yield was significantly enhanced under BMC4 at 42.20 t ha −1 , compared with BMC1 at 21.90 t ha −1 , BMC2 at 19.41 t ha −1 , BMC3 at 25.81 t ha −1 , the fertilised control at 18.75 t ha −1 and non-fertilised control at 11.53 t ha −1 . Only BMC4 showed positive NP balances, suggesting that pasture did not absorb N and P from the existing soil reserve. Soil microbial composition and abundance were not affected by the applied BMC treatments in short term. The benefit–cost ratio ranged from 1.94 to 2.54, indicating economic viability of the BMC products and suggesting a great potential of biochar-based fertilisers for wide adoption to other crops. Graphic abstract