Fertilizer Techniques And Mechanism For Improving Potassium Content Of Flue-cured Tobacco Leaves

Potassium (K) content of flue-cured tobacco leaves in China is universally low which seriously affects the quality of flue-cured tobacco, but recently there are no effective methods to address the problems. Slowly-released K fertilizers are able to provide K nutrient sustainably, reduce the fixation and leaching of soil K, ameliorate crops’growth and development, and improve absorption efficiency of K, which is an effective way to enhance K content of flue-cured tobacco. Through a series of experiments of K nutrient release experiments, pot experiments, field experiments of flue-cured tobacco response to slowly-released potassium fertilizers, Rb tracing experiments and foliar fertilizer experiments, the paper reports the release features of various K fertilizers and their effects on the growth and development, K nutrition, and economic features of flue-cured tobacco as well as the K availability in soils. The major conclusions are as follows:1. Water extraction and soil incubation methods were used to study the nutrient release features of slowly-release fertilizers. The nutrient release features of PV coated potassium nitrate, PV with humic coated potassium chloride, PV coated potassium sulfate all appeared as reverse "L" pattern, with the releasing period of25,40,100days respectively. The nutrient release curves were almost the same in water extraction method and soil incubation method.2. The pot experiments and field crop response experiments of slowly-released potassium fertilizers were conducted to understand the effects of K fertilizers on flue-cured tobacco K content. The results showed that slowly-released K fertilizers increased the K content of flue-cured tobacco. The K contents in flue-cured tobacco leaves treated with PV coated potassium nitrate, PV and humic coated potassium chloride and PV coated potassium sulfate were9.0%-38.0%greater than that in the ordinary treatment. Potassium contents in tobacco leaves under slowly-released fertilizer treatments were all over2.5%, reaching the National standard of high quality tobacco leaves.3. Through the analysis of tobacco-growing soils, we found that slowly-released K fertilizers could sustainably supply K and improve the rapidly-available K content in soil during later period of growth. Slowly-released K fertilizers could also reduce the soil K fixation and leaching so that the nutrients can be kept in the soil plough horizon. Through the field experiments in2012, soil available K contents in soil under potassium sulfate treatment were85.40mg/kg and94.94mg/kg respectively in10-20cm and20-30cm soil layer, which was29.05%lower and69.12%higher compared to the same level under coated potassium sulfate treatment.4. The results showed that the activities of nitrate reductase, superoxide dismutase, peroxydase and catalase were reduced, meanwhile the content of protein and malonaldehyde were raised after topping. However, slowly-release fertilizers improved tobacco’s resistance ability and favored its growth.5. Slowly-release fertilizers could enhance output value, the yield was increased by6.8%-32.1%, and output value of PV coated K fertilizer was12000yuan/hm2higher other treatments..6. The experiments studied the transfering rules of K after topping by means of Rb tracer at upper leaf and soil. The results showed that the K in leaves were transported to roots via stems after topping, meanwhile roots also absorbed K and transported it to shoot. Potassium accumulated in stems and roots during this period results the lower K content in tobacco leaves. In the CK+Upper leaves Rb marked treatment,7days after Rb marked, the Rb content in stems were5.12times and8.23times than that in middle leaves and lower leaves respectively. The K2SO4+Upper leaves Rb mark treatment showed the same trend.7. The results show that the K content of tobacco leaves could be increased by foliage spray of chitosan, xylo-oligosaccharides, KH2PO4and K2SO4in the day of topping and7days later. The K content in upper leaves in the four treatments were2.79%,2.54%,2.65%,2.66%respectively, while2.58%,2.78%,2.94%,2.67%in middle leaves, reaching the national standards of high quality tobacco leaves. The four materials can be used as raw materials of foliar conditioner.