Effect of potassium fertigation on potassium absorption and growth of flue-cured tobacco

ObjectivesThe objective of the experiment is to study effects of various potassium application models on growth, potassium absorption rate and water and fertilizer use efficiencies of flue-cured tobacco, to explore an optimum potassium application method and quantity under the negative pressure irrigation, and to provide some references for high efficient water and fertilizer utilization of flue-cured tobacco.

MethodsA pot experiment was conducted using NC55 as plant material. Taking the recommended potassium application rate of 230 kg/hm² as 100%, the K application rates of 100% (K1), 75% (K2) and 50% (K3) were set up, and the designed potassium was once basally applied into soil (S) or applied with irrigation under the negative pressure irrigation of –15 kPa respectively. The potassium application methods included fertigation (W) and conventional soil fertilization (S). Taking the optimum dosage of potassium 230 kg/hm² under the conventional irrigation as 100%, three levels of potassium dosage, named 100% (K1), 75% (K2) and 50% (K3), were set up. The conventional irrigation without fertilization was chosen as CK, six treatments (SK1, SK2, SK3, WK2, WK3 and CK) were set up. The agronomic traits of tobacco were observed, and dry matter accumulation, potassium absorption rate, utilization rate of potash and water use efficiency (WUE) were determined.

ResultsAt the rosette stage, the plant height, efficient leaf number, leaf length, leaf width, leaf area and other agronomic character indices of the SK2 and SK3 were higher than those of other treatments. But the total dry matter accumulation amounts of the WK2, WK3, SK2 and SK3 were 31.16, 29.26, 29.92 and 28.37 g respectively, the root dry weights were 12.40, 10.51, 11.91 and 10.20 g respectively, and the leaf dry weights were 17.05, 17.01, 15.67 and 16.12 g respectively, all were in order of WK2 > SK2, WK3 > SK3. At the vigorous growing period, the plant weight, stem biomass and leaf dry weight of the WK2 were 99.18, 19.18 and 61.29 g respectively, which were higher than other treatments. At the mature stage, the whole plant weight and leaf dry weight were in order of WK2 > WK3 > SK1 > SK2 > SK3, the whole plant weights were 139.27, 132.60, 124.50, 117.36 and 110.10 g respectively, the leaf dry weights were 93.97, 87.35, 80.33, 78.56 and 74.80 g respectively. During the whole growth period, the WUE was in order of WK2 > WK3 > SK1 > SK2 > SK3, the WUEs were 3.78, 3.54, 3.41, 3.28 and 3.22 g/kg, respectively, indicating that the WUEs of potassium fertilization with water were higher than the conventional method, and the decrease of the dosages of potassium could reduce the WUEs of tobacco plants under the same method. During the whole growth period, the potash use rates were in order of WK2 > WK3 > SK2 > SK1 > SK3, with the values of 43.0%, 42.6%, 21.9%, 20.0% and 18.5% respectively, the potassium uptake of WK2 was 53.85 kg/hm² higher than that of SK2, and the potassium uptake of WK3 was 34.65 kg/hm² higher than that of SK3, showing that potassium fertilization with water was more beneficial to potassium absorption. The potassium utilization rates of WK2 and WK3 were 21.1 and 20.7 percentage points higher than SK2 respectively, indicating that potassium fertilization with water could significantly enhance the potassium absorption and utilization rates under the negative pressure irrigation. The maximum potassium absorption rate was observed at the vigorous growing to top plate period, and the tobacco could maintain relatively larger absorption rate during the whole growth period.

ConclusionsPotassium fertilization with negative pressure irrigation has obvious priorities in: 1) Delaying agronomic traits of tobacco at rosette stage, but promoting the growth at the vigorous growing stage and mature stage, thus increasing accumulation of dry matter and potassium uptake; 2) Improving water use efficiency and potash utilization rate; 3) Maintaining high potassium uptake rate in the whole growth stages of flue-cured tobacco, especially in the middle and later periods.