Effects of increased potassium application under different tillage depths on soil nutrients， root development and potassium uptake of flue-cured tobacco

Objective This study aimed to investigate the effects of increased application of potassium fertilizer on soil nutrients under different tillage depths， root development， potassium metabolism and economic benefits of flue-cured tobacco， with the goal of providing a reference for guiding farmers in proper fertilization and tobacco quality improvement.Method Taking flue-cured tobacco variety CB-1 as the experimental material， a field experiment was conducted by using a two-factor randomized block design. Eight treatments were set under the conditions of conventional tillage （S， 15 cm） and deep tillage （D， 30 cm）： conventional fertilization （S/D）， conventional fertilization+potassium feldspar soil conditioner （ST1/DT1）， conventional fertilization+potassium humate （ST2/DT2）， conventional fertilization+potassium feldspar soil conditioner+potassium humate （ST3/DT3）. Physicochemical indexes of soil （pH， organic matter， alkali-hydrolyzable nitrogen， available phosphorus， available potassium and slowly available potassium）， root indexes （root activity， total root length， root surface area， average root area and root volume）， and indexes of flue-cured tobacco such as potassium accumulation， potassium utilization efficiency， potassium ion channels and relative expression of transporter genes of flue-cured tobacco under different treatments were measured to analyze the effects of different treatments on the economic benefits of flue-cured tobacco.Result Under the same fertilization treatment， the pH values of soil under deep tillage treatments were higher than that under conventional tillage treatment. The organic matter content under ST3 and DT3 treatment was the highest. The content of soil alkali-hydrolyzable nitrogen in each treatment declined as the growth period progressed. The content of available phosphorus in soil was higher under deep tillage treatments than in conventional tillage treatments except during the rosette stage. In both conventional and deep tillage treatments， the content of available potassium in soil showed a trend of first increasing and then decreasing， or a continuous decrease. Under the same tillage depth， the order for slowly available potassium content in each treatment was ST1>ST3>ST2>S and DT1>DT3>DT2>D， respectively. As the growth period of flue-cured tobacco progressed， the root activity of flue-cured tobacco in each treatment increased first and then decreased， and the high root activities were observed in the fast-growth period， with the highest value found in the DT3 treatment. Deep tillage and increased potassium application improved the root growth of tobacco plants， and the DT3 and DT1 treatments showed better effects. At the mature stage， the distribution ratio of potassium in various organs of tobacco plants was in the order of leaves > stems > roots. In the DT3 treatment， the potassium accumulation in each organ and the utilization efficiency of potassium fertilizer were higher， with potassium accumulation for the whole plant reaching 86.22 kg/ha； and the apparent utilization rate， seasonal recovery rate and economic utilization efficiency of potassium fertilizer were 5.58%， 4.33% and 1.89% respectively. Deep tillage and combined with potassium fertilizer could increase the relative expression of NtKC1， NtHAK1 and NtKT12 genes in roots and leaves of flue-cured tobaccos， promote potassium ion transport and improve potassium uptake and accumulation. The economic benefit of flue-cured tobacco under the DT3 treatment was the best， with the yield of 2105.08 kg/ha， the output value of 83113.09 yuan/ha， and the proportion of superior tobacco of 68.17%.Conclusion Under the condition of deep tillage for 30 cm， conventional fertilization combined with potassium feldspar soil conditioner 300 kg/ha and potassium humate 240 kg/ha can increase nutrient content in the soil of tobacco fields， promote root development of tobacco plants， improve the utilization efficiency of potassium fertilizer， up-regulate the relative expression of key genes of potassium ion channels and transporters， thereby increasing the economic benefits of flue-cured tobaccos.