Investigation of interaction effects of biochars and silicon on growth and chemical composition of Zea mays L. in a Ni-polluted calcareous soil

Studies on the interaction effects of silicon (Si) and biochars in potentially toxic element (PTE)-contaminated soils are limited. Thus, the aim of this study was to investigate the interaction effects of biochars, from sheep manure (SMB) and rice husk (RHB) produced at 300 and 500 °C, and 2 levels of Si (as Na metasilicate), on growth and chemical composition of corn ( Zea mays ) in a Ni-polluted calcareous soil. It was found that the combined application of Si and biochars significantly reduced soil available Ni (17-32%) and the corn shoot Ni concentrations (29-58%), associated with soil pH increase (r=0.56-0.60, P<0.01). Among the biochars, SMB increased soil pH the most, and increased soil EC to saline levels, attributed to the higher ash content of SMB. Similarly, increasing Si application levels resulted in increasing soil pH and EC values. Application of all the biochars resulted in significant biomass increases with most positive effect from RHB. Despite the positive effect seen on soil Ni immobilization, the combined application of Si and biochars generally resulted in a decrease in corn shoot biomass yields compared to biochars alone, attributed to the significantly higher soil pH, EC and Na content which resulted in suppression of macro and micronutrient uptake by the corn.