Objectives Soil Cd pollution is concerned for the safety of tobacco cultivation. How to prevent the uptake and transport of Cd by tobacco has been attempted in many ways. The study investigated the effects of foliar fertilizers on reducing Cd uptake and improving tobacco quality to provide a cost effective way for the safe production of tobacco in Cd polluted soils.
Methods A pot experiment was carried out using red clay soil (Cd 0.515 mg/kg), yellow clay soil (Cd 1.862 mg/kg) and cyan clay soil (Cd 1.145 mg/kg), and two cultivars of tobacco, Y-87 and K-326, were selected as tested materials. Taking distilled water as control, three kinds of foliar fertilizers, i.e. organic chelated-Zn foliar fertilizer (FI-1), humic acid chelated-K foliar fertilizer (FI-2) and silica sol iron foliar fertilizer (FI-3), were sprayed on the 21st, 36th and 49th day since the tobacco seedlings were transplanted. At harvest, the biomass of tobacco was weighted, the Cd contents in different parts were determined, and the uptake and tobacco quality indices were measured.
Results 1) Spraying foliar fertilizers significant increased the dry weight of tobacco leaves, and the best effect was observed with fertilizer of FI-1 with a maximum increase of 24.4% in Y-87 and 30.8% in K-326. The less effects were by fertilizer FI-2 and FI-3 and the twos were similar with each other. 2) Compared with control, the Cd contents in the middle leaves of tobacco were decreased significantly (P < 0.05). The average decrement of middle leaf Cd contents for Y-87 and K-326 were 18.0%–35.7% and 26.2%–40.2% in paddy soil, 10.3%–36.1% and 24.8%–42.2% in yellow mud, and 26.1%–33.0% and 19.4%–30.8% in duck feces mud soil. The effect of foliar fertilizers on Cd uptake generally followed the order of FI-1 > FI-2 > FI-3. 3) The total N and K contents in tobacco leaves were increased by spray of foliar fertilizers, and the increase reached significant levels merely by fertilizer FI-1 and FI-2 (P < 0.05). The nicotine and chlorine contents were decreased, and the decrease reached significant levels by fertilizer FI-1 and FI-2 and not by FI-3 (P < 0.05). The ratio of K/Cl, sugar/alkali and N/alkali were increased with foliar fertilizer spraying, especially for FI-1 and FI-2. Except for a slight increase of reduced sugar for FI-3 treatment in duck feces mud, the overall properties of tobacco leaves were in the optimal range for all foliar fertilizers, in particular, the FI-1 and FI-2.
Conclusions Spraying the three foliar fertilizers could significantly inhibit the uptake and upload of Cd by tobacco in the Cd-polluted soils. Meanwhile, the organic chelated-Zn and humic chelated-K fertilizers perform satisfactory in improving the tobacco qualities. Therefore, spraying chelated-Zn and humic chelated-K fertilizers is considered an effective way for the safe and high efficient production of tobacco in Cd-polluted soils
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