1. Why should cotton be ripened with ethephon?

The cotton bolls in the middle and upper part of the cotton bolls mature and crack under the climate conditions of falling temperature in autumn. For various reasons, some cotton bolls in the later stage do not crack and open before the frost and become post-frost flowers, or even cannot crack and become invalid bolls. Especially in the northern cotton region of China, the autumn temperature dropped rapidly, the dry frost came early, and the proportion of flowers after the frost was high, which had a great impact on the yield and quality of cotton. Although the climate conditions in the southern cotton region are stronger than those in the north, due to the high multiple cropping index and tight stubble connection, the area of late-cropping cotton has been expanding in recent years. The contradiction between grain and cotton competing for season, land and labor is very prominent in production, which is not conducive to the early development of cotton, resulting in the late development and late maturity of cotton. At the same time, the late maturity of cotton also affects the timely sowing and normal growth of the following crops. Therefore, late maturity of cotton has been a major problem in production for a long time. Through years of scientific experiments, effective technical measures have been found to solve the problem of late maturity of cotton, which is to spray cotton with ethephon. It can accelerate the development of cotton bolls and make them crack and open bolls early.

Through years of repeated practice in production, it can be concluded that the use of ethephon in cotton has the following advantages.

(1) Early flowering and reduced post-frost flowers: cotton sprayed with ethephon shortened the boll period, making cotton bolls crack and open in advance, and significantly reduced post-frost flowers. According to our experiment, when 100 grams and 125 grams of ethephon were applied to late-maturing cotton per mu, the flowering rate after frost was 23.8% and 21.0%, which was 12.7% and 15.5% lower than that of 36.5% of the control. According to the observation of Beijing Agricultural University, the boll period of cotton bolls flowering from August 9 to 10 is more than 80 days for the control, and the boll number after frost accounts for 50%, while the treated bolls are all boll before frost; The boll period of cotton bolls flowering on August 19 is more than 92 days for the control bolls, all of which are post-frost flowers, while the treated post-frost flowers are only 50%. The reduction of flowers after frost not only increased cotton yield, but also improved fiber quality.

(2) Improve yield and increase economic benefits: under the condition of reasonable use of ethephon, cotton generally has a yield increase effect of 5-10%, and the yield increase in the northern cotton region is greater than that in the south. The grade of cotton sprayed with ethephon has increased, and the unit price of seed cotton has increased. According to the public, the cotton sprayed with ethephon has received early, sold fast, and has good quality and high price. According to the experimental materials in Shanghai, the average yield of seed cotton per mu is 101.6 kg when using ethephon for late-maturing cotton, which is 8.2 kg higher than 93.4 kg of the control, and the yield increase rate is 8.8%; The lint was 39.3 kg, an increase of 3.5 kg and 9.9% over the control 35.8 kg. The reason is that the number of flowers and ineffective bolls decreased after frost, and the boll weight and lint percentage increased. The average economic benefit per mu was 126.18 yuan, an increase of 13.94 yuan over the control of 112.24 yuan. The reason for the increase of income is the increase of unit yield and the increase of unit price of seed cotton. The average unit price of seed cotton per 100 kg is 122.82 yuan, an increase of 4.80 yuan compared with 118.02 yuan of the control. Local experiments also believe that cotton sprayed with ethephon can generally increase the income by more than 10 yuan per mu, and more than 20 yuan. Therefore, it can be considered that cotton spraying with ethephon is a technical measure with small investment, quick effect, large income, wide adaptability and experimental value.

(3) It is beneficial to the growth of subsequent crops and promotes the double high yield of cotton and grain: some fields with double cropping of cotton and wheat in the past could not be pulled out in time due to the late harvest of cotton, so it is customary to directly interplant wheat in the cotton field without tilling, resulting in overgrown weeds and affecting the growth of wheat. After spraying ethephon, the stem can be pulled out early and the wheat can be planted after ploughing, which creates good growth conditions for the wheat. Therefore, spraying ethephon on cotton is also an effective measure to achieve high yield of cotton and grain.

(4) Reduce the number of flower harvesting and save labor: cotton sprayed with ethephon, cotton bolls are concentrated in boll opening, and generally the end of flower harvesting is 3 to 4 times. Therefore, some people say that cotton sprayed with ethephon will have dry flowers in the first tide, prosperous flowers in the second tide, and no flowers in the third tide and the fourth tide, while cotton without ethephon will have to harvest 5 to 6 times. In addition, the cotton sprayed with ethephon has many old leaves falling off, the flowers collected are clean, and the time for picking flowers is saved, thus saving labor.

2. How about the effect of cotton ripening by spraying ethephon?

About 5 days after the proper use of ethephon, the old leaves of cotton gradually turn red from the appearance, and some old leaves fall off later. At the same time, the cotton bolls began to dehydrate, and then the cracking and boll opening were accelerated. The cracking speed of cotton bolls was significantly accelerated 10 days after the treatment, and the cotton bolls concentrated cracking and boll opening was 10 to 25 days after the treatment, and the cotton harvest could be basically ended in about 30 days. For example, in Shanghai, the harvest of late-maturing cotton can be ended by spraying before and after the "cold dew". Since the first frost of the year occurs around November 15, the cotton sprayed with ethephon will spend very little after the frost. According to our observation of the upper bolls, the flowers opened on the same day were listed, and the boll period (flowering → boll opening) of the cotton bolls sprayed with ethephon was 7 to 10 days shorter than that of the cotton bolls not sprayed, and the cotton harvest could end 10 to 15 days earlier.

The field test showed that the effect of ethephon on cotton boll ripening was mainly determined by the concentration of the drug and the temperature at that time. The appropriate concentration of the drug and the appropriate temperature conditions could achieve the ideal ripening effect. The effect of cotton boll ripening is poor when too much medicine is used, especially under low temperature conditions. Secondly, the use of medication devices is also related to the effect of ethephon on ripening cotton bolls. The use of ultra-low volume spray, Dong-16 type foggers, backpack spray, etc. has a good effect on ripening cotton bolls, while the use of Gongnong 36 type motorized spray has a poor effect on ripening cotton bolls due to large fog spots and waste of liquid medicine.

3. What kind of cotton field needs to be ripened with ethephon?

Years of practice has proved that ethephon ripening cotton is an effective technical measure, but not all cotton fields need to use ethephon ripening. In both the northern and southern cotton areas, the use of ethephon to accelerate ripening can achieve good results in cotton fields that are greedy for green and late ripening and have more autumn peaches due to various reasons. This type of cotton field is characterized by late boll opening, large proportion of flowers after frost, and many ineffective bolls, which have a great impact on yield and quality. Especially in the northern cotton area, the dry frost comes early and has a greater impact, so it is more necessary to use ethephon. In addition, for some cotton fields in urgent need of crop change (such as rape seedling fields and vegetable fields), the use of ethylene can make the harvest end in advance, pull out the pole in time, and free up the land to arrange the next crop.

In a region or production unit, the cotton fields that need to be ripened can generally be roughly estimated. However, the fields and areas that need to be ripened with ethephon must be subject to field inspection. According to the growth of cotton beads, the climatic conditions of the year and the needs of crop rotation, reasonable arrangements should be made. Generally, ethephon should not be used for cotton fields that grow normally and mature earlier or have lower yield levels.

4. When is it appropriate to spray ethephon on cotton? How much ethephon should be used per mu of cotton field?

Whether the time of using ethephon is appropriate is the key to the success of ethephon in ripening cotton. If used too early, it will lead to premature senescence and shedding of leaves, which will lead to premature cracking of some cotton bolls due to insufficient development, resulting in reduced boll weight and decreased lint percentage and quality; If it is used too late, due to the low temperature, the efficacy cannot be fully exerted, and even if the dosage is increased, the ideal ripening effect cannot be achieved. According to the test results of each unit, the appropriate time for cotton to use ethephon should be based on the following principles: first, it depends on the development degree of cotton bolls. The cotton bolls can be used only when the boll stage% [boll age (flowering → spraying days) ÷ age (flowering → boll opening days) X100] of most cotton bolls on the cotton bolls is more than 70 (generally the upper boll age reaches 45 days). At this time, the cotton bolls are in the middle and late stage of fiber filling stage. The use of ethephon can promote the delivery of organic nutrients from cotton leaves to cotton bolls. Therefore, the application of drugs at the right time not only plays a role in accelerating the ripening of cotton bolls, but also helps to enrich cotton fiber, increase boll weight and increase lint percentage. For example, in Shanghai, the final flowering stage of cotton is generally in late August, and the appropriate period for using ethephon should be around "cold dew". At this time, the boll period of cotton bolls is more than 70%; Second, within a few days after the use of ethephon, the high temperature should be above 20 ℃ to have obvious ripening effect; The third is to determine the time of using the agent according to the frost period. In northern cotton areas, it is generally appropriate to use ethephon about 20 days before the dry frost. In short, the appropriate time for cotton to use ethephon should be determined according to the cotton growth trend, climate conditions and other factors in different regions and according to local conditions.

The dosage of ethephon shall be based on the principle of economy, effectiveness and safety. The dosage should be determined according to the factors such as cotton growth and climatic conditions. Generally, the dosage can be less for early use (due to high temperature) or medium growth cotton fields; Cotton fields with late use (due to low temperature) or vigorous growth or more autumn peaches will be used more. In the same way, the southern cotton area should use less when the air temperature is higher, while the northern cotton area should use more. Within the range of appropriate dosage, the more the dosage is, the faster the cotton boll ripens. But if the dosage is more than the appropriate dosage, the cotton boll ripens too fast, and the phenomenon of poor boll opening and difficult flower picking will occur, and the flower pedicel has yellow spots. At the same time, the leaves often fall off too early and too much, which will affect the weight and quality of the bolls, and even the young bolls fall off. In addition, the agricultural cost has also been increased. The results showed that it was appropriate to use 100~150 grams of stock solution per mu (containing 40% of the effective ingredient of ethephon) to accelerate cotton ripening in practical production. Take Shanghai as an example, cotton with more autumn peaches in normal years is generally used before the end of September, and the ethylene utilization per mu should not exceed 100 grams; For those used before or after October 10, about 125 grams per mu; It is used in the middle of October and can be used to about 150 grams per mu. Of course, in actual use, the dosage should be determined according to the temperature conditions at that time.

5. What is the physiological reason for ethephon to ripen cotton bolls?

Senescence is a normal growth process of plants, but it is related to external environmental conditions such as temperature, light, fertilizer and water, and is also regulated by plant endogenous hormones and controlled by genetic genes. In agriculture, it is sometimes necessary to delay aging and ripening to increase the yield of field crops or keep fruits and vegetables fresh; Sometimes it is necessary to accelerate aging to promote precocity. Therefore, regulating the senescence of crops has important production significance. The use of ethephon in cotton is a process to accelerate the aging of cotton bolls. Studies have proved that the ripening of cotton bolls by ethephon is not a simple dehydration and ripening process, but a normal physiological metabolism process to accelerate development and promote maturity.

The experiment proved that cotton boll and cotton leaf can absorb ethephon and quickly decompose and release ethylene in the body. The cotton bolls showed two release peaks two days after ethephon treatment and before boll opening, while those without ethephon treatment only showed one release peak before cracking, and the time was 8 days later than the second ethylene release peak of the treated cotton bolls, which was consistent with the fact that ethephon promoted boll opening 7 to 10 days earlier. Since ethylene is recognized as a fruit ripening hormone, it can be considered that ethephon is the physiological reason for ripening cotton bolls, The main reason is that the ethylene content in the cotton boll is increased, the development of the cotton boll is accelerated, and the ethylene release peak that must occur before the cotton boll cracks comes ahead of time, thus the cracking and boll opening of the cotton boll is earlier. After the cotton leaf absorbs ethephon, it not only releases ethylene from the leaf itself, but also can transport it to the cotton boll at the same fruit node at a very fast speed. The amount of ethylene in the cotton boll can be measured twice as much as that in the control in two hours, but it will be two days after the treatment when a large amount of ethylene is transported to the cotton boll and reaches the peak. At the same time, ethylene can also be delivered to the cotton bolls above the same fruit branch, but not to the cotton bolls below the same fruit branch. The ethephon absorbed by the cotton boll only releases ethylene in the cotton boll itself, not to the cotton leaf at the same node.

Peroxidase is also an indicator of plant senescence. According to the measurement of Beijing Agricultural University, the peroxidase activity in the cotton boll was improved after ethephon treatment, especially the peroxidase in the boll shell reached a high level, and reached a high value when the boll cracked. The boll cracking was positively correlated with the peroxidase activity in the boll shell. However, the peroxidase content in the shell of the control cotton boll was relatively stable until it gradually rose to the maximum value before cracking, which was significantly delayed than that of the ethephon treatment.

From the above research results, it can be concluded that the essence of ethephon ripening cotton bolls may be that after ethephon treatment, the ethylene released from cotton bolls increases and the peak of ethylene release comes ahead of time, while ethylene promotes the activity of peroxidase and the maximum of peroxidase comes ahead of time, Because peroxidase can accelerate the decomposition and destruction of auxin (generally believed to have the effect of inhibiting aging and delaying maturity), the content of auxin decreases, thus changing the balance between the original ethylene and auxin. It is due to the increase of ethylene in the cotton boll, the increase of enzyme activity, the change of hormone balance and other reasons that promote the transformation of the cotton boll to maturity and aging, thus accelerating the cotton boll cracking and boll opening.

6. What is the relationship between the effect of ethephon on ripening cotton bolls and the temperature at that time?

Using ethephon to ripen cotton bolls, considering the development of cotton bolls, the later the time is, the more beneficial it is. However, the effect of ethephon is closely related to the temperature at that time. If the temperature is low, the effect cannot be exerted. This is because ethephon is different from other desiccants. It is not through simple physical or chemical action to destroy the cell membrane to make the bell shell lose water and crack, but through a complex physiological and biochemical process. These activities require a certain appropriate temperature, and must have a certain effective accumulated temperature to carry out smoothly. According to our measurement, cotton bolls only release a small amount of ethylene at 17~19 ℃ after spraying ethephon on pearl cotton, and only release a large amount of ethylene at above 20 ℃. Cotton bolls without ethrel basically do not release ethylene under 19 ℃. According to the regression equation analysis, the ethylene released by cotton bolls was significantly positively correlated with temperature. Therefore, when using ethephon on cotton, pay attention to the temperature at that time.

7. Why does the boll weight and lint percentage of cotton increase after proper use of ethephon, but decrease if it is improperly used?

Cotton ripening with ethephon is in the late growth stage of cotton. Therefore, among the components of cotton yield, boll weight and lint percentage are closely related to ethephon treatment. The effect of ethephon on boll weight and lint percentage mainly depends on the development degree of cotton bolls. The experimental data from different regions agree that ethephon can increase the boll weight and lint percentage of cotton bolls with boll period of more than 70%. Why? Through 14C tracing, we found that after ethephon treatment, the retention and consumption of Tonghua substances in cotton leaves can be reduced, and the assimilation substances stored in the original cotton leaves and the new assimilation substances after treatment can be more transported to the cotton boll, especially the assimilation substances transported to the cotton boll can be accumulated in more quantities in the cotton boll. This shows that ethephon can increase boll weight and lint percentage by changing the distribution proportion of cotton photosynthetic products, improving the economic coefficient of photosynthetic products, and promoting cotton fiber filling. Therefore, the use of ethephon on cotton bolls with a basic length can increase the boll weight and lint percentage.

However, in other cases (such as insufficient boll period or excessive ethylene utilization), the boll weight and lint percentage will be reduced. Because, under the correct use of ethephon, the appearance of cotton bolls does not change much within 3 to 5 days, the leaf color gradually turns red within 5 to 7 days, the appearance of cotton bolls does not change much within 3 to 5 days, the cotton leaves turn red obviously within 2 to 3 days, even fall off, and the cotton bolls mature very quickly. The study found that after ethephon treatment, the photosynthetic capacity of cotton bolls changed little in one week, and then decreased significantly after one week. This change had little impact on the cotton bolls that had basically grown, but it was extremely unfavorable for the cotton bolls that had not yet grown. Due to the premature aging of functional leaves, the photosynthetic capacity decreased, the organic nutrients obtained by cotton bolls decreased significantly, and the cotton fiber matured before it was enriched, thickened, and matured, thus resulting in the reduction of boll weight, The percentage of clothes drops.

8. Does the use of ethephon in cotton have adverse effects on cotton fiber quality?

Use ethephon to accelerate cotton ripening, as long as the cotton fiber