Potassium Release Characteristics Of Slow-Released Potassium Fertilizer And Applying Effect Of The Fertilizer

Tobacco is a very important economic crop in China.Crude tobacco and cigarette output from China accounts for 30%and 32%of the world's production respectively,but the export part only occupies 3.5%and 1.8%of the world's capacity. In China,The main reason for lower export is the lower quality of crude tobacco caused by the low potassium content in the leaves.Not only the output and production value but also the average price and the ratio of highest quality tobacco leaves are determined by fertilization in present tobacco culture system.So,fertilization,under the conditions of definite environment and varieties,is the key technology to control the output and quality of tobacco leaves.Improving potassium content of tobacco leaves to achieve excellent and optimized tobacco leaves by scientific and economical fertilization are the key methods for tobacco production.The "dissolution rate in water" and "dissolution rate in soil" methods were used to study the potassium nutrient release characteristics of coated potassium fertilizer (CPF) and screen the appropriate types of the slow-release potassium fertilizer (SRPF).And by pot culture experiments and field sampling,the application effects of different kinds of fertilizer and different dosage of slow-release potassium fertilizer B on agronomic features,photosynthetic characteristics,contents of carbon and nitrogen compounds,enzyme activities relating carbon and nitrogen metabolism, phytohormone contents in root and stem tips,mineral contents in different organs, contents and ratio of chemical components in baked tobacco leaves,output and production values were studied to provide scientific theoretical foundation for manufacture,application and development of tobacco slow-release potassium fertilizers.The results were as follows:1.The potassium nutrient preliminary solubility rate of the five potassium fertilizers,which were designed and manufactured according to nutrient requirement of tobacco during growth and development in Hunan Province,was 11.12%,10.76%, 10.93%,11.31%and 10.82%,and the differential solubility rate of them was 3.01%, 2.71%,1.37%,1.43%and 2.58%respectively.The potassium nutrient preliminary solubility rate of CPF-3 and CPF-4 was less than 15%,and the differential solubility was between 0.25%and 2.5%,which met with the international recognized standard for evaluating the nutrient release characteristic of slow-release fertilizers.Thus, CPF-3 and CPF-4 was named slow-release potassium A and slow-release potassium B respectively.The effect of pH on SRPF-B was smaller than that on SRPF-A,pH 6.0 was found optimal for nutrient release.The effects of temperature and fertilizer-water ratio on potassium nutrient release characteristics were larger than other factors.The potassium nutrient release velocity of SRPFS was increased 1.32～3.21 times with every 20℃from 20℃to 60℃.The nutrient release and spread were affected by soil water content and the potassium nutrient release speed and accumulation content of fertilizers were the greatest when soil water content was 75%.2.The main agronomic features of leaf growth and unfolding,leaf length,height, stem girth and maximum leaf area were remarkably influenced by applying SRPF-A and SRPF-B.The effects of SRPFS on leaf breadth and the numbers of valid leaves were unobvious.It was the rapid dry matter accumulation period 45 to 75d after transplanting.The dry matter accumulation speed in leaves was quicker than that in roots and stems.The order was SRPF-B＞75%SRPF-B＞50%SRPF-B＞tobacco special formulated fertilizer(TSFF).The activities of root systems were strongest at 45d after transplanting,which was strengthened after topping because the growth centre was changed.The growth and development,fresh weight and volume,nutrient absorption and transportation of root systems,and the quality of tobacco leaves were improved by applying SRPF-A and SRPF-B Applying SRPF-B showed significant difference in root system activities from other treatments.3.IAA,GA₃ and ZR contents in root and stem tips were increased,and ABA decreased by applying SRPF-A and SRPF-Bbefore topping.The IAA,GA₃ and ZR content was highest in SRPF-N treatment,and ABA content was lowest among the treatments.ZR and ABA contents in root and stem tips were increased gradually with growth and development of tobacco,but GA₃ and IAA contents were reached the peak 45 days after transplanting.The IAA content of stem tips in SRPF-B treatment was as 1.85,1.44,1.97 times as that of control and 1.16,1.21,1.26 times as that in TSFF treatment 30d,45d,60d after transplanting respectively.Applying SRPF-B decreased PUT and SPM contents and increased SPD content in root systems.Polyamine content was less affected by kinds than by dosage of fertilizer.Decreasing fertilizer dosage increased PUT,SPM and SPD contents.4.The content of total chlorophyll and chlorophyll a/b at later stage were increased by applying SRPF-B and 75%SRPF-B.The NR activities in TSFF treatment was the highest at 40d after transplant.However,at 50d after transplant,the NR activities in SRPFS treatment were highest,SRPF-B showed better effect than SRPF-A.The content of protein in plant from TSFF treatment was higher than that from SRPF-B and SRPF-A treatment in early stage,but reversed in later stage.The nicotine content was reduced when decreasing dosage of SRPF-B,the order of nicotine content in leaves was topper leaf＞middle leaf＞lower leaf.The content of total sugar and reduced-sugar was increased as growth and development of tobacco, which was enhanced by fertilization.Reduced-sugar/total sugar was increased and quality of tobacco leaves improved by applying SRPF-B and 75%SRPF-B.5.The contents of mineral elements in different organs of tobacco kept on high level at later stage by applying SRPF.K in tobacco leaves was higher in SRPF-B treatment,and Ca and Mg were lower than that in SRPF-A and TSFF treatments. Most of mineral elements in roots,stems and leaves decreased gradually with the growth and development of tobacco plants.6.Increasing K content leaded to decreasing Ca and Mg content in leaves.The content of N,P,K,Ca and Mg reduced gradually as the growth and development of tobacco.The contents of total N,K and reduced-sugar were enhanced,but the contents of P,Ca,Mg,nicotine and chlorine were decreased by applying SRPF. Contents of total sugar and reduced-sugar were higher than the standards.K content was above 2.0%in treatments applying SRPF-B and 75%SRPF-B The N/nicotine ratio,K/Cl ratio and sugar/nicotine were increased by applying SRPF-B. Comprehensive analysis of the contents and ratio of all kinds of chemical constitutions showed that applying SRPF-B and 75%SRPF-B produced the best results.The yield and economic value were higher applying SRPF-A and SRPF-B compared with using tobacco special formulated fertilizer.Although yield in treatment of 75%SRPF-B was lower than that of SRPF-B,the average price of tobacco leaves was higher because the quality of tobacco leaves was improved.Therefore,it is possible to reduce cost and increase income by applying 75%SRPF-B instead of pure in practical production.