Tobacco stalk biochar in heavy metal contaminated soil amendments with tobacco production

Abstract

To assess the impacts of tobacco stalk biochar on tobacco (Nicotiana tabacum) growth and leaf yield, soil properties and metal immobilization in soil, and non-bioavailability to plants in a soil contaminated with Cu, Pb, and Cd, a pot experiment with biochar application rates of 0, 20, 40, and 80 g·kg-1 was conducted in Pingshan Experimental Ground in Zhejiang A&F University in 2016. And the biochar was mixed with 4 kg soil filled into plastic pots in a randomized design with 4 replications per treatment. Results compared to the control with no biochar additions, showed increases in soil pH, soil fertility, and soil enzyme activity indices as well as a decrease in soil heavy metal bioavailability with increasing application of biochar from 20 g·kg-1 to 80 g·kg-1. With a biochar application rate to the soil of 80 g·kg-1, content of soil organic matter and soil available P increased significantly (P < 0.05) (2.0 and 3.4 times, respectively), and the geometric mean of enzyme activities (GMea) also significantly increased (P < 0.05) (24.8%). Additionally, 40 g·kg-1 of biochar added to the soil led to the highest immobilization effect with decreases on Cu (33.7%) and Pb (29.5%) in the soil. Furthermore, with addition of biochar to the soil both number of tobacco leaves and foliar biomass increased significantly (P < 0.05). With a biochar application rate of 40 g·kg-1 to the soil, foliar fresh biomass was highest at nearly 50% higher than the control. At the same application rate of biochar to soil (40 g·kg-1), Cu and Cd concentrations in tobacco leaves significantly decreased (P < 0.05) to the lowest level. Thus, it may be feasible to use biochar derived from tobacco stalk waste to remediate metal-contaminated soils which can then be re-used for tobacco cultivation, and based on this study, 4% would be a suitable application rate for the biochar.