Impact of Synchronizing the Application of Different Biochar Organic Fertilisers with NPK on Soil Chemical Properties and Growth of Leek (Allium ampeloprasum)

Biochar is a popular organic soil amendment around the world. However, some factors still hinder its full agronomic potentials including low nutrient concentrations especially of aromatic biochar charred from nutrient-poor biomass. Improving the nutrient quality of this type of biochar may necessitate its combined application with organic and or inorganic fertilisers. This study, therefore, aimed to explore the synergistic effects of synchronizing the addition of biochar organic fertilisers with NPK on soil chemical properties and the growth and yield of leek (Allium ampeloprasum). A pot experiment with soil amendments constituting six treatments was conducted. The treatments included; the non-amended control, NPK fertiliser, CLB + NPK, CLB alone, NPOM + NPK, NPOM alone. CLB was made by mixing 80% livestock compost and 20% oak biochar. NPOM was made by pelletizing a mixture of 30% oak biochar, 50% castor bean expeller cake, 10% used coffee grounds and 10% rice bran. The oak biochar was pyrolysed for 3 hours at 600°C. Each of the biochar organic fertiliser was added to the soil at a rate of 2% (15 tonnes per hectare, considering a depth of incorporation of 5 cm with a bulk density of 1000 kg m-3). The results of the synchronized applications varied between the two organic fertilisers. CLB + NPK showed synergistic effects both in amelioration of soil chemical properties and leek growth and yield while NPOM + NPK elicited adverse effects on leek growth and yield. In conclusion, combined application of NPK and biochar organic fertilisers may or may not have synergistic effects depending on the characteristics of the biochar organic fertiliser used.