| Tobacco is one of the most important economical crops in Chongqing. Both yield and quality of tobacco are subjected to many factors such as climatic conditions, soil fertility, fertilizers, varieties, planting and curing technique. Among these factors, fertilization is the core of regulating the yield and quality of tobacco in given climate condition and tobacco variety. Furthermore, reasonable rate of fertilizer and rato of nitrogen (N), phosphorus (P) and potassium (K) were the key technology to guarantee for high-quality tobacco production. Compared with10years ago, status of soil fertility in tobacco growing areas in Chongqing has greatly changed due to continous application of NPK compound fertilizer. For example, soil alkali hydrolyzable N, total N content have increased significantly, and content of soil P and K have changed. Those previous formula and amount of fertilizers is no longer suitable for tobacco planting now. In order to find the suitable amount and formulation of fertilizer for tobacco planting in current soils, field experiment and lab analysis were conducted to study the response of growth, yield, quality of tobacco and soil nutrient content in the post harvest soil to different reduction of N, P and K, and their response to adjustment of the ratio of NPK fertilizer, aiming to provide scientific basis for tobacco planting in Chongqing. The major results were shown as follows:(1) When N rate was increased by22.5kg/hm2on the basis of recommended N rateplant height, leaf number of tobacco was inhibited, the output value and the average price was declined, although these changes were not significant. When N rate was reduced by22.5kg/hm2, the mentioned situation was similar. Without N application, plant growth was severely inhibited, and agronomic benefit, yield and output value of tobacco was all decreased obviously. With the increasing rates of N fertilizer, the content of total N, nicotine and protein in tobacco leaf was increased, whereas the content of reducing sugar was decreased especially in upper leaves. (2) When P rate was increased by50%on the basis of recommended chemical P fertilizer (94.5kg/hm2), the yield and value output of tobacco showed an increased trend but without significant difference, the Shmuck value and ratio of K to chlorine (C1) in flue-cured tobacco was optimized, and the quality of tobacco leaf was improved to some extent. Reduceing50%of phosphate fertilizer resulted in slow grow in early stage, and significant decline in the yield and output value of flue-cured tobacco.(3) When K rate was increased by50%on the basis of recommended chemical K fertilizer (285kg/hm2), the yield and output value of tobacco was not significantly affected. But this resulted in increased content of K in tobacco leaves, optimized ratios of N to nicotine, sugar to N, sugar to nicotine, K/Cl and Shmuck value in tobacco leaf, a better coordination of intrinsic chemical composition in tobacco leaf, and an improved quality of tobacco. Reducing50%of K fertilizer resulted in advanced growth period, the earlier flowering phenomenonthe, and finally significant decrease in yield and output value of flue-cured tobacco.(4) Moderate reducing basal fertilizer on the basis of recommended fertilization stategy which was widely adopted in Chongqing in2013(750kg/hm28-15-25compound fertilizer and organic fertilizer600kg/hm2as basal fertilizer,20-15-10compound fertilizer75kg/hm2as seedling fertilizer, NK compound fertilizer or potassium nitrate225kg/hm2as topdressing fertilizer, and NPK ratio of8.4-8.7-19.8during whole growth period), had no affect on yield and output value of tobacco. Reduction of the basal fertilizer within30%of the conventional rate of fertilizer has no significant effect on the yield and output value of tobacco.10%of reduction of conventional fertilization showed the highest yield and output value. However, excessive reduction of fertilization can significantly decrease the yield and output value of tobacco. For example, the yield decreased by22.4%and the output value decreased by23.9%when the rate of reduction is greater than40%. With the increase of reduction, the amount of N and P uptake by tobacco was decreased. Among all treatments,10%of reduction in conventional fertilization showed the best quality in tobacco leaves.(5) The results of reduced N fertilization and adjustment of NPK ratio showed that moderate reduction of N fertilizer on the basis of farmers’ practice (126kg/hm2) can improve the yield and output value of tobacco.15%of reduction in N fertilizater showed the best in yield, output value, averaged price and proportion of tobacco leaves with first rank, which were5%higher in yield and6.2%higher in output value than farmers’ practice. The yield and output value in treatments of reducing the nitrogen fertilizatier 5%,10%,15%are higher than the treatment of conventional fertilizater, although the difference was not significant. The growth of tobacco, yield and quality of tobacco leaf was affected if N rate was excessively reduced. The growth of tobacco in later period was inhibited, the amount of NPK absorbed by tobacco was significantly decreased, both of which affected the nutrient uptake, yield and output value of flue-cured tobacco when20%or30%of N was reduced.(6)The best ratio of N, P2O5and K2O was1:1.21:2.75on the basis of application of N with108kg/hm2(that is15%reduction of tranditional N rate). The plant grows well and their agronomic traits were better with NPK ratio of1:1.21:2.75. Reducing P or K in this treatment resulted in worse growth and development of tobacco. NPK ratio of1:1.21:2.41had the tallest heigh of tobacco plants but larger pitch, resulting poor growth. In aspect of yield, averaged price and output value of tobacco, NPK ratio of1:1.21:2.75showed the best. When reducing the ratio of P and K at the same time (NPK ratio was1:1:2.41), the yield decreased by22.3%and output value decreased by19%compared with NPK ratio of1:1.21:2.75. In aspect of nutrient uptake, the treatment with NPK ratio of1:1.21:2.75had better effect on NPK absorption and utilization. Similarly, treatment with NPK ratio of1:1.21:2.75had a better chemical components and coordination than other treatments.Overall, the current results showed that it’s possible to reduce the N rate of farmer conventional practice (126kg/hm2). In aspect of growth, yield, output value, quality and nutrient utilization, the optimium range of N rate was105-112.5kg/hm2, meanwhile with NPK ratio of1:1.21:2.75. However, the practicability of reducing N fertilizer strategy and adjustment of NPK ratio should be further verified in future in major tobacco growing areas of Chongqing. |
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