Matched cultivation method for ultralow-nicotine tobacco variety

Abstract

The invention discloses an ultra-low nicotine tobacco variety matching cultivation method, and relates to the technical field of crop characteristic variety cultivation. Comprising the following steps that a tobacco cultivation field and a tobacco variety to be cultivated are selected, seedling raising is carried out, nitrogen is reasonably applied to the tobacco cultivation field, tobacco seedlings are transplanted to the tobacco cultivation field, topdressing is carried out on tobacco regularly, insect pest prevention is carried out in a chemical insect prevention mode, tobacco plants are topped, leaves are reserved, and harvesting is carried out when the tobacco is mature; according to the method, the low-nicotine flue-cured tobacco new strain CD01 is used as a material, the content of alkaloid and the quality of tobacco leaves can be effectively regulated and controlled by reasonably setting the nitrogen application amount, the number of left leaves and the planting density in the tobacco cultivation process, the nicotine content can be kept below 0.8%, the requirement of low-nicotine cigarettes for raw materials can be met, and therefore the economic character of the tobacco leaves is improved, and the tobacco quality is improved. The chemical components of the tobacco leaves are more coordinated, and the quality and yield of the tobacco leaves are ensured while the nicotine content of ultralow-nicotine varieties is not increased.

Description

Technical Field

[0001] The invention relates to the technical field of cultivation of special crop varieties, and in particular to a matching cultivation method for ultra-low nicotine tobacco varieties. Background Art

[0002] Tobacco (scientific name: Nicotiana tabacum) is a plant belonging to the genus Nicotiana of the Solanaceae family. It contains alkaloids such as nicotine. After fermentation, drying and processing, tobacco leaves can be used to make various tobacco products. Alkaloids are an important class of chemical components in tobacco plants, among which nicotine is the most important alkaloid in common tobacco, accounting for 90% to 95% of the total alkaloids. It is synthesized in the roots and transported to the aboveground leaves through the woodlem for accumulation. Nicotine is an important physiologically active ingredient in tobacco leaves and smoke, which can enter brain cells through the blood and produce physiological reactions. It is also considered to be an important component that can make tobacco leaves addictive.

[0003] The nicotine content of tobacco leaves is mainly affected by genetics, ecology, agronomy and other measures. The production methods of low and ultra-low nicotine tobacco leaves mainly include conventional breeding, genetic engineering and agronomic regulation. At present, new low-nicotine variant materials are constantly being discovered or created, and new varieties bred based on these materials are also constantly coming out. Among them, CD01 bred in my country and NC926 bred by North Carolina State University in the United States have attracted much attention. Since agronomic measures such as planting density, nitrogen application amount, and number of leaves left are closely related to the nicotine content of tobacco leaves, it is very important to explore the supporting cultivation technology of low-nicotine varieties.

[0004] The production of low-nicotine tobacco leaves is not only related to the health of smokers, but also involves the sustainable development of the tobacco industry. The production of low-nicotine tobacco leaves depends on the selection and breeding of low-nicotine varieties and low-nicotine agronomic cultivation technology. Traditional tobacco varieties have a high nicotine content, and the supporting cultivation technology is based on ensuring that the tobacco leaves have a high nicotine content. Fertilization, topping and other measures are adopted to ensure that the tobacco leaves have sufficient strength and fragrance. The ultra-low nicotine varieties are aimed at producing ultra-low nicotine content tobacco leaves. If traditional cultivation technology is used, the nicotine content will inevitably increase, which cannot meet the development and use of low-nicotine cigarette products.

[0005] At present, the nicotine content of ultra-low nicotine varieties is below 0.1%, which has not yet met the requirements of the World Health Organization. Therefore, the nicotine content of tobacco leaves should be further reduced through the implementation of cultivation technology, or at least the nicotine content of tobacco leaves should be ensured not to increase. However, if the nitrogen application rate is reduced too much, the density is too high, and the number of leaves left is too large, it is bound to cause a decrease in tobacco yield, a decrease in aroma quality, and a decrease in tobacco farmers' income. The production of tobacco raw materials cannot be guaranteed. Therefore, the present invention proposes a supporting cultivation method for ultra-low nicotine tobacco varieties to solve the problems existing in the prior art. Summary of the invention

[0006] In view of the above problems, the purpose of the present invention is to propose a supporting cultivation method for ultra-low nicotine tobacco varieties to solve the problem in the prior art that, due to the chemical composition characteristics and growth and development characteristics of ultra-low nicotine varieties, the existing conventional tobacco variety cultivation technology is not suitable for ultra-low nicotine tobacco varieties, and it is impossible to ensure the quality and yield of tobacco leaves while ensuring that the nicotine content of ultra-low nicotine varieties does not increase.

[0007] In order to achieve the purpose of the present invention, the present invention is implemented by the following technical scheme: a method for cultivating ultra-low nicotine tobacco varieties, comprising the following steps:

[0008] Step 1: Select soil with both effective nitrogen content and soil clay particles that meet the standards as tobacco cultivation fields, then select the tobacco varieties to be cultivated and use the floating seedling cultivation method to cultivate them;

[0009] Step 2: Deeply plow and level the tobacco cultivation field selected in step 1, and then apply the compound at 2.55 kg / mu, and transplant the tobacco seedlings to the tobacco cultivation field at a row spacing of 1.2 m × 0.5 m after the tobacco seedlings grow to 65 days;

[0010] Step 3: After the tobacco seedlings are planted in the tobacco cultivation field, topdress the tobacco regularly and use chemical insect control methods to prevent and control pests and diseases;

[0011] Step 4: After the tobacco plants have grown for 105 days in the tobacco cultivation field, the tobacco plants are topped and 18 leaves are left per plant. The tobacco plants are harvested after they mature.

[0012] Further improvements are: in the step 1, the effective nitrogen content meets the standard of no more than 90 ppm, the soil clay content meets the standard of no more than 20%, and the selected tobacco variety is the ultra-low nicotine variety CD01.

[0013] A further improvement is that in step one, the specific steps of using floating seedling cultivation to cultivate tobacco seedlings are: firstly floating a foam plug tray filled with a lightweight seedling cultivation matrix on the water surface, then sowing tobacco seeds on the seedling cultivation matrix, and the tobacco seedlings take root and grow on the seedling cultivation matrix to grow seedlings.

[0014] A further improvement is that the lightweight seedling matrix is ​​formed by mixing peat, perlite, vermiculite, coconut bran, coconut shreds and agricultural and forestry waste in a mass ratio of 3:1:1:1:1:2, and the agricultural and forestry waste is formed by mixing rice husks, sawdust, corn cobs and straw in a mass ratio of 1:1:1:1.

[0015] A further improvement is that in the step 2, the compound fertilizer is prepared by mixing nitrogen, phosphorus pentoxide and potassium oxide, and the mixing mass ratio of nitrogen, phosphorus pentoxide and potassium oxide is 1:1:2.

[0016] A further improvement is that in step three, the frequency of topdressing the tobacco is once every 18 days, the amount of topdressing is 0.55 kg / mu, and the fertilizer used for topdressing is prepared by mixing potassium sulfate, potassium nitrate and superphosphate in a mass ratio of 1:1:1.

[0017] A further improvement is that in step three, the specific steps of chemically controlling tobacco plants are: firstly applying chlorpyrifos to the tobacco plants in the tobacco cultivation field by spraying, and then applying chlorpyrifos to the tobacco plants in the tobacco cultivation field by smoke.

[0018] A further improvement is that in the step 4, the topping and leaf-retaining operation is carried out in sunny weather, and after the tobacco plants are toppled and leaf-retaining is completed, the axillary buds are removed to avoid damaging the tobacco leaves when harvesting the tobacco.

[0019] The invention has the following beneficial effects: the invention uses the low-nicotine flue-cured tobacco new strain CD01 as material, and can effectively regulate the alkaloid content and tobacco leaf quality by reasonably setting the nitrogen application amount, the number of leaves left, and the planting density during the tobacco cultivation process, so that the nicotine content can be maintained below 0.8%, and the requirements of low-nicotine cigarettes on raw materials can be met, thereby improving the economic traits of tobacco leaves, making the chemical components of tobacco leaves more coordinated, and ensuring the quality and yield of tobacco leaves while ensuring that the nicotine content of ultra-low nicotine varieties does not increase, which has important theoretical and practical significance for achieving high-quality and high-yield low-nicotine tobacco leaf production, provides a scientific basis for the production of low-nicotine tobacco, and provides new theoretical and practical support for the sustainable development of the tobacco industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 It is a schematic diagram of the process of the supporting cultivation method of the ultra-low nicotine tobacco varieties of the present invention. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] See also Figure 1 This embodiment provides a method for cultivating ultra-low nicotine tobacco varieties, comprising the following steps:

[0024] Step 1: Select tobacco cultivation fields and tobacco varieties to be cultivated and raise seedlings

[0025] Selecting soil with an effective nitrogen content of no more than 90ppm and a soil clay content of no more than 20% as a tobacco cultivation field for tobacco cultivation is conducive to the vigorous growth of tobacco plants in the later stage. Considering the disease resistance, yield and quality of the variety, this embodiment selects the ultra-low nicotine variety CD01 as the tobacco variety to be cultivated, and adopts a floating seedling cultivation method to cultivate seedlings. The specific steps are: first float a foam plug tray containing a lightweight seedling cultivation matrix on the water surface, and then sow tobacco seeds on the seedling cultivation matrix. The tobacco seedlings take root and grow on the seedling cultivation matrix, and the seedlings can absorb water and nutrients from the matrix and the water bed. Compared with the traditional seedling cultivation method, it is more environmentally friendly and efficient, can reduce the labor for transplanting, save the land for seedling cultivation, facilitate the management of tobacco seedlings, and is conducive to cultivating strong seedlings and improving the seedling rate;

[0026] The lightweight seedling medium used in this embodiment is composed of peat, perlite, vermiculite, coconut bran, coconut shreds and agricultural and forestry waste in a mass ratio of 3:1:1:1:1:2, wherein the agricultural and forestry waste is composed of rice husk, sawdust, corn cob and straw in a mass ratio of 1:1:1:1;

[0027] Step 2, rationally apply nitrogen to the tobacco cultivation field and transplant the tobacco seedlings to the tobacco cultivation field. The tobacco cultivation field selected in step 1 is deep-ploughed and leveled, and then compound fertilizer is applied according to the nitrogen application amount required in Table 1 below, avoiding excessive application of nitrogen fertilizer to reduce the synthesis of nicotine. The compound fertilizer is prepared by mixing nitrogen, phosphorus pentoxide and potassium oxide in a mass ratio of 1:1:2. After the tobacco seedlings grow to 65 days, the tobacco seedlings are transplanted to the tobacco cultivation field at a row spacing of 1.2m×0.5m. By rationally controlling the nitrogen application amount and tobacco plant spacing in the tobacco cultivation field, the alkaloid content and tobacco leaf quality can be effectively regulated, the economic traits of tobacco leaves can be improved, and the chemical composition of tobacco leaves can be more coordinated;

[0028] Step 3: Regularly apply fertilizer to tobacco and use chemical insect control to prevent pests

[0029] After the tobacco seedlings are planted in the tobacco cultivation field, the tobacco is top-dressed once every 18 days, the amount of top-dressing is 0.55 kg / mu, the fertilizer used for top-dressing is prepared by mixing potassium sulfate, potassium nitrate and superphosphate in a mass ratio of 1:1:1, and chemical insect control is used to prevent and control pests and diseases, and the specific steps are: first, chlorpyrifos is applied to the tobacco plants in the tobacco cultivation field by spraying, and then chlorpyrifos is applied to the tobacco plants in the tobacco cultivation field by smoke;

[0030] Step 4: Topping the tobacco plants and leaving the leaves and harvesting when the tobacco is mature

[0031] After the tobacco plants have grown to 105 days in the tobacco cultivation field, they are topped and the leaves are retained according to the number of leaves required in Table 1 below. The topping and leaf retention operation is performed in sunny weather and should be avoided on rainy days because rainy days are not conducive to wound healing. After the tobacco plants are toppled and leaf retained, their axillary buds are removed to prevent the growth of axillary buds from consuming nutrients and affecting the yield and quality of tobacco leaves. By reasonably controlling the number of leaves retained, the growth height of tobacco and the number of side branches are controlled, the maturity of tobacco leaves is promoted and the quality is improved. The tobacco plants are harvested after they mature, and the tobacco leaves are avoided from being damaged when harvesting.

[0032] Test methods

[0033] The ultra-low nicotine variety CD01 was used as the test material, and floating seedling cultivation was adopted. The soil fertility was moderate and uniform, the soil was loose, the terrain was flat, the structure was good, and there were good irrigation conditions. The pH of the cultivated layer soil was 8.40, containing 13.73g / kg of organic matter, 50.05mg / kg of alkaline nitrogen, 1.48g / kg of total nitrogen, 0.81g / kg of total nitrogen, 0.51g / kg of total phosphorus, 16.69g / kg of total potassium, 13.16mg / kg of available phosphorus, and 176mg / kg of fast-acting potassium.

[0034] The experiment adopted a two-factor split-plot design. The main plot was nitrogen application (N), with three different levels, namely N1: 2.1kg / mu, N2: 2.55kg / mu, and N3: 3.0kg / mu; the sub-plot was the number of leaves left (L), with three different levels, namely L1: 16 pieces / plant, L2: 18 pieces / plant, and L3: 20 pieces / plant; there were 9 treatments in total, each treatment was repeated 3 times, and there were 27 plots in total; the row spacing was 1.2m×0.5m, and a protective row was set. The fertilizers were tobacco-specific compound fertilizer (N: P2O5: K2O = 1: 1: 2), potassium sulfate, potassium nitrate, and superphosphate, and the weight of the applied phosphorus fertilizer and potassium fertilizer was kept consistent; according to the nitrogen application rate and the number of leaves left, the experiment set up a total of 9 treatments, and the treatment results are shown in Table 1 below. 2kg of flue-cured tobacco from B2F and C3F of each treatment was selected for the determination of chemical composition and sensory quality of tobacco leaves;

[0035] Table 1 Nitrogen application rate and number of leaves left in the experiment

[0036]

[0037] 1) According to the "Investigation and Measurement Methods of Tobacco Agronomic Traits" (YC / T 142-2010), 10 representative tobacco plants were selected in each plot for marking, and their plant height, stem girth, internode distance, leaf number, maximum leaf length and leaf width were measured at the vigorous growth stage and dome stage;

[0038] 2) The chemical composition content was determined using a AAⅢ continuous flow chemical analyzer (BRAN+LUEBBE, Germany) in accordance with the Tobacco and Tobacco Products Standard System (YC / Z 240—2008);

[0039] 3) Alkaloids were determined by gas chromatography according to tobacco industry standard YC / T161-2002. Under alkaline conditions, 200 mg of the sample was extracted with methyl tert-butyl ether (MTBE), and the contents of nicotine, nornicotine, anatabine, and anabasine were quantitatively detected by gas chromatography-hydrogen flame ionization detector (GC-FID) (Agilent 7890A, Agilent Technologies, USA) with n-hexadecane as internal standard.

[0040] 4) Grading tobacco leaves according to the grading standards of "Flue-cured Tobacco" (GB 2635-1992), and evaluating the appearance quality of graded tobacco leaves in terms of leaf structure, maturity, oil content, color, chroma, and identity;

[0041] 5) After the mature tobacco leaves in the upper part of each plot are harvested, they are hung and braided into poles and then dried on the same kang. According to the standards of "Flue-cured Tobacco" (GB 2635-1992), the flue-cured tobacco leaves are graded, the grade structure and average price are calculated, and the economic traits such as single leaf weight, yield, and output value are calculated;

[0042] 6) The flue-cured tobacco of each treatment B2F and C3F was cut into shreds and rolled into single-ingredient tobacco, which was evaluated and scored by smoking experts from Henan China Tobacco Industrial Co., Ltd. and the National Cultivation Physiology and Biochemistry Research Base of Henan Agricultural University. The evaluation was carried out in accordance with the "Standard Sensory Evaluation Method for Tobacco and Tobacco Products" (YC / T138-1998). The detection indicators included aroma quantity, aroma quality, concentration, impurities, strength, irritation, aftertaste, and combustibility.

[0043] EXCEL 2016 and SPSS22.0 software were used for data processing and statistical analysis, and Duncan method was used for multiple comparisons. The results are as follows:

[0044] As shown in Table 2 below, in the vigorous growth period, with the increase of nitrogen application rate, the agronomic traits of CD01 showed an upward trend. In the dome stage, under the same nitrogen application rate, with the increase of the number of leaves, the plant height increased significantly, the stem girth, the length and width of the largest leaf showed a decreasing trend, and the internode had no obvious change pattern. Under the same level of the number of leaves, except for the internode, the plant height, stem girth, the length and width of the largest leaf increased significantly with the increase of nitrogen application rate (Note: Different lowercase letters in the table below indicate significant differences among treatments (P<0.05), N, L and N×L represent nitrogen application rate, number of leaves and the interaction between the two, "**" indicates extremely significant differences (P<0.01), and "*" indicates significant differences (P<0.05));

[0045] Two-way ANOVA showed that the effect of nitrogen application rate on plant height reached an extremely significant level, the effect on stem girth and maximum leaf length reached a significant level, and the effect on node distance and maximum leaf width was not significant; except for the node distance, the effect of the number of leaves on various agronomic traits reached an extremely significant level, and the interaction between the two had no significant effect on the agronomic traits of CD01.

[0046] Table 2 Statistical table of the effects of nitrogen application rate and number of leaves left on agronomic traits of CD01

[0047]

[0048] As shown in Table 3 below, in the vigorous growth period, the effect of nitrogen application on the nicotine and alkaloid content of CD01 fresh tobacco leaves reached a significant level, and the nicotine and total alkaloid content increased with the increase of nitrogen application. In the dome stage, at the same level of the number of leaves left, the nicotine and alkaloid content increased with the increase of nitrogen application; at the same nitrogen application level, with the increase of the number of leaves left, the nicotine and alkaloid content decreased. Only trace amounts of anabasine and anatabine were detected under the T1, T4, and T7 treatments, and nornicotine was not detected under each treatment. The two-way ANOVA showed that the effects of nitrogen application and the number of leaves left on the nicotine and alkaloid content reached an extremely significant level, and the interaction between the two had no significant effect on the nicotine and alkaloid content of fresh tobacco leaves in the dome stage.

[0049] Table 3 Effects of nitrogen application rate and number of leaves left on alkaloid content in fresh tobacco leaves of CD01 during growth period

[0050]

[0051] As shown in Table 4 below, for the middle leaves, at the same nitrogen application level, the nicotine and total alkaloid contents decreased significantly with the increase of the number of leaves left. At the level of L1 and L2, the nicotine and total alkaloid contents increased first and then decreased with the increase of nitrogen application. At the level of L3, the nicotine, anabasine and total alkaloid contents increased with the increase of nitrogen application. Anatabine was not detected under each treatment. Two-way ANOVA showed that the effects of nitrogen application, the number of leaves left and their interaction on the contents of nicotine, nornicotine, anabasine and total alkaloids reached extremely significant levels.

[0052] Table 4 Effects of nitrogen application rate and number of leaves left on alkaloid content in the middle leaves of CD01 after baking

[0053]

[0054] As shown in Table 5 below, for the upper leaves, at the same nitrogen application level, the nicotine and total alkaloid contents decreased significantly with the increase of the number of leaves left. At the same level of the number of leaves left, the nicotine and total alkaloid contents showed an upward trend with the increase of nitrogen application. Anatabine was not detected under any treatment. The two-way ANOVA showed that the effects of nitrogen application, number of leaves left, and the interaction between the two on the contents of nicotine, nornicotine, anabasine, and total alkaloids were extremely significant.

[0055] Table 5 Effects of nitrogen application rate and number of leaves left on alkaloid content in upper leaves of CD01 after baking

[0056]

[0057] It can be seen from Table 6 below that for the middle leaves, under the same nitrogen application level, with the increase of the number of leaves left, the total sugar, reducing sugar and chlorine contents first increased and then decreased, the total nitrogen and potassium contents decreased, and the potassium-chlorine ratio first decreased and then increased; under the N1 and N3 nitrogen application levels, the nitrogen-alkali ratio and the sugar-alkali ratio first increased and then decreased with the increase of the number of leaves left, under the N2 nitrogen application level, the nitrogen-alkali ratio and the sugar-alkali ratio increased with the increase of the number of leaves left, when the number of leaves left was constant, the total sugar, reducing sugar and chlorine contents decreased with the increase of nitrogen application, and the total nitrogen, potassium content and potassium-chlorine ratio increased with the increase of nitrogen application; under the L1 and L2 levels of the number of leaves left, the nitrogen-alkali ratio first decreased and then increased with the increase of nitrogen application; under the L3 level of the number of leaves left, the nitrogen-alkali ratio first increased and then decreased with the increase of nitrogen application; under the L1 and L3 levels, the sugar-alkali ratio decreased with the increase of nitrogen application; under the L2 level, the sugar-alkali ratio first decreased and then increased with the increase of nitrogen application. Two-way ANOVA showed that nitrogen application rate and number of leaves left had extremely significant effects on the chemical components of the middle leaves of CD01; the interaction between the two had extremely significant effects on the total sugar, reducing sugar, chlorine content, nitrogen-alkali ratio and sugar-alkali ratio of the middle leaves of CD01.

[0058] Table 6 Effects of nitrogen application rate and number of leaves left on chemical components of the middle leaves of CD01

[0059]

[0060] As shown in Table 7 below, for the upper leaves, at the same nitrogen application level, with the increase in the number of leaves left, the total sugar and reducing sugar contents first increased and then decreased, the total nitrogen, potassium content and potassium-chlorine ratio decreased, and the chlorine content showed an upward trend. At the N1 and N3 nitrogen application levels, the nitrogen-alkali ratio first increased and then decreased with the increase in the number of leaves left, and at the N2 nitrogen application level, the nitrogen-alkali ratio first decreased and then increased with the increase in the number of leaves left; at the N1 nitrogen application level, the sugar-alkali ratio first increased and then decreased with the increase in the number of leaves left; at the N2 and N3 nitrogen application levels, the sugar-alkali ratio increased with the increase in the number of leaves left, and when the number of leaves left was constant, the total sugar, reducing sugar and chlorine contents increased. , sugar-alkali ratio decreased with the increase of nitrogen application rate, while total nitrogen, potassium content and potassium-chlorine ratio increased with the increase of nitrogen application rate; at L1 and L3 levels, nitrogen-alkali ratio increased first and then decreased with the increase of nitrogen application rate; at the level of L2 for the number of leaves left, nitrogen-alkali ratio increased with the increase of nitrogen application rate, and two-way ANOVA showed that nitrogen application rate and number of leaves left had extremely significant effects on the chemical components of the upper leaves of CD01; two-way ANOVA showed that nitrogen application rate and number of leaves left and their interaction had extremely significant effects on the total sugar, reducing sugar, total nitrogen, potassium, chlorine content, nitrogen-alkali ratio and sugar-alkali ratio of the upper leaves of CD01;

[0061] Table 7 Effects of nitrogen application rate and number of leaves left on the chemical composition of the upper leaves of CD01

[0062]

[0063] As shown in Table 8 below, with the increase of nitrogen application or the decrease of the number of leaves left, the tobacco leaves changed from thin to thick, and the color changed from light to dark. Under the treatment of nitrogen application of N1, the overall looseness of the tobacco leaves was still loose, and under the treatment of nitrogen application of N1, the leaf structure was still loose, and the overall chromaticity of the tobacco leaves was weak. The appearance quality of the tobacco leaves under the treatments of T5, T6, and T8 can be evaluated as excellent as a whole, which is specifically manifested in orange color, high maturity, loose structure, sufficient oil content, strong or thick chromaticity, and small damaged area, and thus the tobacco leaves have high industrial utilization rate. In particular, the tobacco leaves under the treatment of T5 have the most oil content and the smallest damaged area, so they have the highest score in appearance quality.

[0064] Table 8 Effects of nitrogen application rate and number of leaves left on the appearance quality of CD01

[0065]

[0066] As shown in Table 9 below, under the same nitrogen application level, the single leaf weight of tobacco leaves decreased with the increase of the number of leaves left. Under the N1 level, the average price, output value and the proportion of high-quality tobacco decreased significantly with the increase of the number of leaves left. Under the N2 and N3 levels, the average price, output value and the proportion of high-quality tobacco increased first and then decreased with the increase of the number of leaves left. Under the same level of leaves left, the single leaf weight of tobacco leaves increased significantly with the increase of nitrogen application. Under the L1 level, the average price increased first and then decreased with the increase of nitrogen application, and the output value and the proportion of high-quality tobacco increased with the increase of nitrogen application. Under the L2 and L3 levels, the average price, output value and the proportion of high-quality tobacco increased first and then decreased with the increase of nitrogen application. Under the T7 treatment, the tobacco yield was the highest, which was 2757.25 kg·hm -2 ; Under T3 treatment, tobacco leaf yield was the lowest, only 2265.37 kg·hm -2 Under T5 treatment, the tobacco leaf output value was the highest, which was 61930.71 yuan / hm2. -2 ; Under T3 treatment, tobacco leaf output value was the lowest, which was 49113.14 yuan / hm2 -2 Overall, the average price, output value and proportion of high-quality tobacco under T5, T8 and T9 treatments were higher, and the economic benefits were good. T5 was the best, with an average price, output value and proportion of high-quality tobacco of 24.55 yuan / kg and 61930.71 yuan / hm2, respectively. 2 , 79.63%. Two-way ANOVA showed that nitrogen application rate and number of leaves had no significant effect on the proportion of medium and high-quality tobacco leaves, but had extremely significant effects on single leaf weight, average price, total yield and output value; the interaction between the two had a significant effect on the total yield and proportion of medium and high-quality tobacco leaves of CD01, and had an extremely significant effect on the average price and output value;

[0067] Table 9 Effects of nitrogen application rate and number of leaves left on economic traits of CD01

[0068]

[0069] It can be seen from Table 10 below that, at the same nitrogen application level, the aroma quality, aroma quantity, concentration, strength, aftertaste and total score were all higher in the treatment with L2 leaves, and the strength decreased with the increase of the number of leaves left; under the treatment with N1 nitrogen application, there were significant differences in the effects of different numbers of leaves left on the scores of aroma quality, aroma quantity, miscellaneous smell and strength. At the same nitrogen application level, different numbers of leaves left had no significant effect on concentration, irritation, aftertaste and total score. At the same leaf level, the aroma quality, aroma quantity, concentration, strength and aftertaste showed an upward trend with the increase of nitrogen application. Among them, when the number of leaves left was L2 and L3, the aroma quantity and miscellaneous smell scored the highest at the N2 nitrogen application level, and the irritation and total score first increased and then decreased with the increase of nitrogen application; there was no difference in combustibility among the treatments. The sensory quality of the middle leaves was evaluated as best in T5 treatment, with the highest total score of 49.1 under T5 treatment, and the aroma quality and aroma volume were significantly higher than those of other treatments. Two-way ANOVA showed that the effects of nitrogen application rate on the aroma quality, aroma volume, miscellaneous smell, strength and irritation of the middle leaves of CD01 were extremely significant; the effects of the number of leaves left on the aroma quality, miscellaneous smell and strength of the middle leaves of CD01 were extremely significant, and the effects on the aroma volume and irritation were significant. The effects of nitrogen application rate and the number of leaves left on the total score of the sensory quality of the middle leaves of CD01 were significant, and the interaction between the two had no significant effect on the sensory quality of the middle leaves of CD01.

[0070] Table 10 Effects of nitrogen application rate and number of leaves left on sensory quality of CD01 middle leaves

[0071]

[0072] It can be seen from the following Table 11 that, under the same nitrogen application level, the sensory quality scores were higher in the treatment with the number of leaves retained as L2, and there were significant differences in the effects of different numbers of leaves retained on the scores of aroma quantity and strength, and no significant effects on the scores of aroma quality, concentration, miscellaneous smells, irritation, aftertaste and combustibility. Under the same leaf retention level, the aroma quality, aroma quantity, concentration, strength, irritation, aftertaste and total score showed an upward trend as the nitrogen application rate increased. Only at the L1 level, the number of leaves retained had significant differences in the effects of different nitrogen application rates on the scores of aroma quality and strength, and no significant effects on the aroma quantity, concentration, miscellaneous smells, irritation, aftertaste, combustibility and total score. The sensory quality of the upper leaves was better in T5 and T8 treatments as a whole, with total scores of 49.0 and 49.2 under T5 and T8 treatments, respectively. The aroma quality, aroma quantity, miscellaneous odors, strength, irritation and burningness were consistent. Only the concentration and aftertaste of T8 were slightly higher than those of T5, but there were no significant differences. Two-way ANOVA showed that the nitrogen application rate had an extremely significant effect on the aroma quality and aroma quantity of the upper leaves of CD01, and a significant effect on the concentration, strength and total score. The number of leaves left had an extremely significant effect on the aroma quantity and strength of the upper leaves of CD01, and a significant effect on the aroma quality, miscellaneous odors, irritation and total score. The interaction between the two had no significant effect on the sensory quality of the upper leaves of CD01.

[0073] Table 11 Effects of nitrogen application rate and number of leaves left on sensory quality of upper leaves of CD01

[0074]

[0075] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for cultivating ultra-low nicotine tobacco varieties, characterized in that: The following steps are involved: Step 1: Select soil with both effective nitrogen content and soil clay particles that meet the standards as tobacco cultivation fields, then select the tobacco varieties to be cultivated and use the floating seedling cultivation method to cultivate them; Step 2: Deeply plow and level the tobacco cultivation field selected in step 1, and then apply the compound at 2.55 kg / mu, and transplant the tobacco seedlings to the tobacco cultivation field at a row spacing of 1.2 m × 0.5 m after the tobacco seedlings grow to 65 days; Step 3: After the tobacco seedlings are planted in the tobacco cultivation field, topdress the tobacco regularly and use chemical insect control methods to prevent and control pests and diseases; Step 4: After the tobacco plants have grown for 105 days in the tobacco cultivation field, the tobacco plants are topped and 18 leaves are left per plant. The tobacco plants are harvested after they mature.

2. The method for cultivating ultra-low nicotine tobacco varieties according to claim 1, characterized in that: In the step 1, the effective nitrogen content meets the standard of no more than 90 ppm, the soil clay content meets the standard of no more than 20%, and the selected tobacco variety is the ultra-low nicotine variety CD01.

3. The method for cultivating ultra-low nicotine tobacco varieties according to claim 1, characterized in that: In the step 1, the specific steps of using floating seedling cultivation to cultivate tobacco seedlings are: firstly floating a foam plug tray filled with a lightweight seedling cultivation matrix on the water surface, then sowing tobacco seeds on the seedling cultivation matrix, and the tobacco seedlings take root and grow on the seedling cultivation matrix to grow seedlings.

4. The method for cultivating ultra-low nicotine tobacco varieties according to claim 3, characterized in that: The lightweight seedling raising matrix is ​​formed by mixing peat, perlite, vermiculite, coconut bran, coconut shreds and agricultural and forestry wastes in a mass ratio of 3:1:1:1:1:2, and the agricultural and forestry wastes are formed by mixing rice husks, sawdust, corn cobs and straws in a mass ratio of 1:1:1:

1.

5. The method for cultivating ultra-low nicotine tobacco varieties according to claim 1, characterized in that: In the step 2, the compound fertilizer is prepared by mixing nitrogen, phosphorus pentoxide and potassium oxide, and the mixing mass ratio of nitrogen, phosphorus pentoxide and potassium oxide is 1:1:

2.

6. The method for cultivating ultra-low nicotine tobacco varieties according to claim 1, characterized in that: In the step three, the frequency of topdressing the tobacco is once every 18 days, the amount of topdressing is 0.55 kg / mu, and the fertilizer used for topdressing is prepared by mixing potassium sulfate, potassium nitrate and superphosphate in a mass ratio of 1:1:

1.

7. The method for cultivating ultra-low nicotine tobacco varieties according to claim 1, characterized in that: In the step 3, the specific steps of chemically controlling the tobacco plants are: firstly applying chlorpyrifos to the tobacco plants in the tobacco cultivation field by spraying, and then applying chlorpyrifos to the tobacco plants in the tobacco cultivation field by smoke.

8. The method for cultivating ultra-low nicotine tobacco varieties according to claim 1, characterized in that: In the step 4, the topping and leaf-retaining operation is carried out in sunny weather, and after the tobacco plants are toppled and leaf-retaining is completed, the axillary buds are removed to avoid damaging the tobacco leaves when harvesting the tobacco.

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