| Recently,large areas of agricultural land in China have been contaminated with heavy metals,which has adversely affected agricultural production,including tobacco crops.Previous studies showed that biochar may be used as an amendment for immobilization of heavy metals and reducing their bioavailability in soils,as well as promoting plant growth.Therefore,a pot experiment was carried out to investigate the effect of different biochars on the growth and quality of tobacco crop.The impact of biochar application on the bioavailability of heavy metals(Cd,Cu,Pb and Zn)was also evaluated.Biochars derived from coconut shell,bamboo sawdust,dead pig and tobacco stalk were applied to the tobacco-planting soil at 3%(W/W).After 150-days of growth of tobacco plants,the physical and chemical properties of the soil samples,the plant biomass,agronomic and quality tobacco leaves,and the concentrations of heavy metals in the tobacco leaves were determined.The main results are as following.(1)Effect of biochar on the physical and chemical properties of tobacco-planting soil.Results from the pot experiment showed that the bamboo biochar treatment had significant(p<0.05)effect on soil electrical conductivity and water content.A significant(p<0.05)increase in soil pH was observed at the tobacco biochar treatment.Moreover,the addition of the pig biochar significantly increased the concentration of organic carbon,total N,total P,available P,exchangeable K and Na in the soil,whereas the concentration of exchangeable Ca decreased significantly.In addition,the activities of catalase and urease significantly increased with the pig biochar treatment.The concentrations of extractable Cd,Cu and Pb in soil decreased with the coconut shell biochar and bamboo biochar treatments,whereas the pig biochar treatment significantly increased the extractable Zn in soil.The pig biochar appeared to be more effective in improving the nutrient level and enzyme activities of the tobacco-planting soil,whereas the coconut shell and bamboo biochars were more effective in reducing concentration of the extractable heavy metals than other biochars.In addition,tobacco stalk biochar had significant effect on the soil physical properties.(2)Effect of the biochars on the growth rate and quality of tobacco plantsThe results showed that the addition of the pig biochar significantly(p<0.05)increased the stem girth,fresh weight and dry matter weight of tobacco plants,and significantly(p<0.05)improved the quality and uniformity of the upper,middle and lower leaves of flue-cured tobacco.All four biochar treatments significantly reduced the Cd accumulation in the upper leaves of tobacco plants.Furthermore,the tobacco stalk biochar were effective in reducing the concentration of Cd in the middle and lower leaves,and Pb in the upper leaves of tobacco plants.The addition of the pig biochar significantly reduced the Cu accumulation in the middle leaves.The concentration of Cd in the lower leaves significantly decreased in the bamboo biochar treatment.Generally,the concentration of heavy metals in tobacco leaves at different positions varied with the biochar treatments.Overall,the biochar amendment can reduce heavy metal accumulation in tobacco leaves.The pig biochar was more effective at promoting tobacco plant growth and improving the quality of tobacco flue-cured tobacco leaves than the other biochars.Therefore,biochars derived from different feedstock biomass materials have different effect on immobilization of heavy metals in soil and the growth and quality of the tobacco crop. |
