Winter cellaring technology for the prevention of frost damage by grafting seedlings of large bell jujubes
It was funded by the "100 Million Talents Project" training fund of Liaoning Province.
_Yao Lijie, etc
Big bell jujube is a unique excellent variety of large fruit jujube tree in Chaoyang City, Liaoning Province, and is a national geographical indication protection product approved by the state in 2010, generally using sour jujube seedlings to make rootstock, and cultivating big bell jujube seedlings through grafting. Due to the special climate of Chaoyang area, spring drought, large temperature difference between day and night, early spring, high temperature, low ground temperature, when the aboveground part of the big bell jujube seedling has sprouted, the underground part has not yet thawed, the root system can not absorb water, transpiration causes serious water loss in the dried body of the aboveground part of the seedling, resulting in the death of the grafted seedling. In recent years, the frequency of frost damage in the grafted seedlings of big bell jujube in Chaoyang area has reached 30% to 40%, which has directly caused major economic losses to the seedlings and garden construction of big bell jujube seedlings. Since 2003, Chaoyang Longdu Forest Fruit Development Co., Ltd. and Liaoning Provincial Dryland Agriculture and Forestry Research Institute have cooperated to develop a new technology for preventing frost damage from grafting seedlings of big bell jujube seedlings, and after 16 years of continuous discussion and experimental research, we have innovated the new technology of winter cellaring of big bell jujube grafted seedlings to prevent frost damage, which is reported below.
1 Overview of the test site
The test site is located at latitude 41 ° 35 ′ north and longitude 120 ° 25 ′ east, located in Zhao Du Ba Village, Zhao Du Ba Town, Old Town, Chaoyang City, Liaoning Province. It is a warm temperate arid monsoon continental climate, with four distinct seasons, more arid spring, less rain and wind, and large evaporation; hot summer, large light intensity, uneven distribution of rainwater, mostly concentrated in July and August; less rain in autumn, large temperature difference between day and night; less snowfall in winter, dry and cold. The average annual precipitation is 481 mm, the annual frost-free period is 158 d, and the average sunshine hours are 2 900 h. The annual average temperature is 8.4 °C, the annual extreme maximum temperature is 40.6 °C, the annual extreme minimum temperature is -31.1 °C, and the difference between the coldest and hottest months of the year is 35.2 °C. The total area of the test is 7.33 hm 2, of which the area of the big bell jujube nursery area is 4.67 hm 2.
2 Symptoms of frost damage of grafted seedlings
The frost damage of the grafted seedlings of the big bell jujube in Chaoyang District, Liaoning Province, generally occurs in the early spring season, which mainly harms the seedlings planted in the garden, and the symptoms of frost damage before the seedlings are not obvious. Seedlings in the afforestation field after planting to return to green when the frost damage symptoms appear, if it is in mid-to-late April afforestation, after the beginning of May frost damage symptoms will be continuously manifested, the occurrence site above the seedling dry grafting interface below 20 cm below, the obvious symptom is the seedling dry phloem and xylem burst out of separation, resulting in the newly planted grafted seedlings before germination and leaf spitting death, the mortality rate is as high as 90%, seedling fees and afforestation project costs are basically all lost.
3 Analysis of the causes of frost damage
Big bell dates are generally sown with sour dates to make rootstocks, and seedlings are cultivated by grafting. Because sour dates are wild varieties, drought-tolerant, suitable for growing in poor soil, the water content in the body is relatively low, and the big bell jujube is a large fruit type jujube variety, like water and fertilizer, and the water content in the body is relatively high. The use of sour dates as rootstock, big bell dates as scion, and cultivation of big bell jujube grafting seedlings, from their respective biological characteristics, there are certain differences in water demand, which is the internal factor that the grafted seedlings of big bell dates are prone to frost damage. The external cause is due to the special climate in the Chaoyang area, spring drought, large temperature difference between day and night, early spring, high temperature, low ground temperature, when the aboveground part of the big bell jujube seedling has sprouted, the underground part has not yet thawed, the root system can not absorb water, transpiration causes the seedling to lose water balance above the graft interface, coupled with the high daytime temperature, cell tissue activities, night temperature drops to the freezing point below the cell water ice, so that the victim part of the formation layer cells repeatedly freeze and thaw, resulting in cytoplasm tearing death. Through the combined action of internal and external factors, the grafted seedlings of the big bell jujube are extremely susceptible to frost damage.
4 Research and development ideas for new technologies to prevent frost damage
The large bell jujube grafting seedlings overwinter, through winter and spring, the span is close to half a year, and the frost damage phenomenon in that year is unpredictable. In 2002, Chaoyang Longdu Linguo Development Co., Ltd. cultivated 70,000 big bell jujube grafting seedlings, due to the seedlings overwintering nakedly, it happened that serious frost damage occurred in the year, resulting in all the large bell jujube grafting seedlings produced frozen to death, and the company caused direct economic losses of more than 180,000 yuan. To this end, in view of the problem of overwintering antifreeze damage of big bell jujube grafting seedlings, we inspected chaoyang county, Lingyuan city and Beipiao city in Chaoyang area to cultivate large seedlings of big bell jujube grafting seedlings, and the results of the inspection results were that all counties (cities) in the city did not have effective control methods. Therefore, it is necessary to develop a new cellar technology for the prevention of frost damage by grafting seedlings of large bell dates. There are 3 research and development ideas: 1) avoid wind and cold and direct sunlight; 2) seedlings are fresh and living, and a sufficient amount of ventilation space should be maintained when storing, and the cover cannot be in direct contact with the seedlings, leaving a certain height; 3) The cover should play a role in the appropriate amount of gas exchange inside and outside. This experimental research work follows the principle of step-by-step, and has gone through a long research and development process of optimal depth and width of winter storage cellars, sand type selection, sand mixing ratio, reasonable number of plants per bundle of seedlings, ventilation space height, cover material selection, and ventilated cellaring.
5 Test material
The rootstock is a 1-year-old seeded seedling of sour dates, the seeds are from Chaoyang City, and the scion comes from the company's big bell jujube garden. The test site is flat, the soil name is brown soil, the texture is loam soil, and the soil thickness is thick soil. Large bell jujube grafting seedlings are generally 2-year seedlings. The mulch is straw curtains, corn straw, sorghum straw, etc. The wooden pole supporting the cover is generally 2.4 to 2.5 m long and the diameter of the small head is more than 10 cm. The sand used is fine sand, with a fineness modulus of 1.6 to 2.2 and an average particle size of 0.250 to 0.125 mm.
6 Results and analysis
6.1 Specifications of winter cellars
The maximum frozen depth of the Chaoyang region after the 1970s was 105 cm, and the minimum value reached 79 cm by the beginning of the 21st century. In 2011, the winter cellar was tested with 7 different depth tests, including 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7 m, and 5 different width tests such as 0.8, 1.0, 1.2, 1.4 and 1.6 m. Experimental results show that the low-cost and easy-to-operate winter cellar specifications are suitable for depth of 1.5 m and width of 1.2 m.
6.2 Space is reserved for the top and upper cover of the seedlings
Before entering the cellar, the grafted seedlings of the big bell jujube should be treated whole, the side branches and tops of the seedlings should be cut off, the branches should be 1.5 cm, and the top tips should be removed by 20 to 30 cm. Based on the average height of the pruned seedlings of 80 cm, the distance between the top and upper cover of 30, 50, 70 and 90 cm was carried out, and the experimental results showed that the optimal space height was about 70 cm.
6.3 Effect of watering time of seedlings on frost damage of seedling skin after cellaring
In 2012, an experiment was conducted on the effect of watering time of seedlings on frost damage in the skin of seedlings. The grafted seedlings of the big bell jujube are generally watered once before the cellar is sealed after the cellar, that is, before November 22 (or 23), that is, before the snow festival, to increase soil moisture. At this time, it is the season that begins to freeze, and it is necessary to master the watering time, otherwise it is easy to cause frost damage to the skin of the seedlings. The experimental results show that from 6:00 in the morning to 19:00 in the evening, the best watering time is between 11:00 and 13:00, and the rate of frozen plants in the skin is 0, which will not cause any harm to the skin part of the seedling (Table 1).
Table 1 Effects of watering time of seedlings after cellaring on frost damage in the skin of seedlings
6.4 Number of seedlings in winter cellaring
In 2013, the number of seedlings was tested in winter. Set 6 treatments of 5, 10, 15, 20, 25 and 30 plants per bundle, repeat 3 times, and tie 2 with polyethylene tie strips, of which 1 is tied above the seedling grafting interface and one is tied in the middle of the seedling trunk. The experimental results show that the close connection between the seedling roots and the soil and sand mixture is the best, and the number of bundles without heat in the roots before the seedlings come out of the cellar is 5 plants per bundle and 10 plants per bundle, of which the effect and economic optimal number of bundled plants are 10 plants per bundle (Table 2).
Table 2 Number and effect of seedlings in winter cellaring
6.5 Optimal Coverage
From 2011 to 2013, corn straw, sorghum straw and straw curtains were experimented on as cellar coverings. The experimental results show that the effect of corn straw and sorghum straw as cellar coverings is not good, and the reason for the analysis is that after the straw of these two crops is covered, the gap is relatively large, the air flow in the cellar and outside the cellar is large, and the seedlings are prone to "cold". The best cellar covering is a straw curtain, when the temperature is not higher than -6 ~ -5 °C, first cover a layer of straw curtains; when the temperature drops to -15 °C, cover another layer of straw curtains. These 2 layers of straw curtains play a role in the exchange of weak air flow in the cellar and outside the cellar, that is, they play an antifreeze damage effect, and they also achieve the effect that the seedlings are not hot before going out in the spring.
7 Key technologies for winter cellaring of grafted seedlings
7.1 Excavation of winter cellars
The depth of the winter cellar is 1.5 m and the width is 1.2 m. The optimal distance between the top of the seedling after the cellar (after pruning) and the upper cover retains ventilation space is about 70 cm. The length of the winter cellar depends on the number of seedlings.
7.2 Prepare to support straw curtain wooden poles and fine sand soil
Poles and fine sand depend on the number of seedlings.
7.3 Seedlings
The seedling start time is from November 1 to 8, that is, 6 to 7 days before the beginning of winter.
7.4 Seedlings are temporarily fake planted on the nursery
In the process of seedling raising, with the false planting, with the wet soil to use wet soil to plant the seedlings in situ, the root system is all cultivated with wet soil, and the thickness of the cultivated soil is not less than 10 cm.
7.5 Whole branch treatment of seedlings
On 22 (or 23 November), before the snow freezes, the temporarily fake seedlings are processed before they are put down the cellar. Cut off the side branches and tips of the seedlings, leave the branches at 1.5 cm, and remove the top tips by 20 to 30 cm.
7.6 Cover transport and grading of seedlings
In the process of transporting the whole branch treated seedlings to the winter cellar, grass curtain covering measures should be adopted. Before the seedlings enter the cellar, they are graded, generally divided into three levels, requiring the diameter of the first-level seedling land ≥ 0.8 cm; the diameter of the second-level seedling field ≥ 0.7 cm, the < 0.8 cm; the third-level seedling diameter ≥ 0.6 cm, the < 0.7 cm. Height is not used as a basis for grading large bell jujube seedlings.
7.7 Spread the mixed sand to the bottom of the winter cellar and water and moisturize
A certain amount of wet soil is mixed with fine sand soil in the same amount, that is, the mixing ratio is wet soil: fine sand soil = 1:1. The thickness of the paving should not exceed 50 cm. In the 7 to 10 d before the seedlings enter the cellar, it is necessary to check the humidity of the mixed sand soil after the cellar, if it is found dry, it is necessary to water once to ensure that when the seedlings are in the cellar, the soil is loose and the humidity is moderate, and it is advisable to hold the hand into a ball.
7.8 Seedling cellar
When the seedlings are in the cellar, they should be graded into the cellar, one bundle per 10 plants, and the root system is placed vertically downwards to ensure that the mixed sand soil of the seedling roots is soft, and the soil is placed one by one, and the depth of the mixed sand soil is more than 10 cm above the grafting interface.
7.9 After the seedlings are in the cellar, water them again
The watering time is on November 22 (or 23), and the best time to water is to choose to do it at noon to prevent the dry seedlings and the surface layer of the roots from freezing (dipped in wax), affecting the survival rate of the seedlings.
7.10 Seedling cellars
After the light snow festival on November 22 (or 23), before the heavy snow festival on December 7 (or 8), when the temperature is not higher than -6 ~ -5 °C, first cover a layer of straw curtains, cover the upper side of the winter cellar, supported by a wooden pole horizontally, the wooden pole is suitable for a length of 2.4 to 2.5 m, the diameter of the small head is 10 cm, and the length of the cellar is placed vertically, and one is placed every 1 m spacing. When the temperature drops below -15 °C, cover it with a straw curtain. To prevent the straw curtain from being blown open by the wind, it should be pressed with a wooden stick or a branch.
7.11 Wintering management
During the wintering of seedlings, regular inspections should be carried out to prevent high winds from rolling up the grass curtains. If there is any sign that the grass curtain is rolled up by the wind, cover it in time. During the seedling cellaring period, in case of snowfall, the snow on the cover should be removed in time.
7.12 Management of seedlings before leaving the cellar
Before the Qingming Festival on April 5 (or 6) in spring, check the soil moisture in the cellar, and if the mixed soil is found to be dry, water once to maintain the humidity. After the Qingming Festival, remove the straw curtain on the top floor.
7.13 Management of the transportation of seedlings after they are left in the cellar
When the seedlings come out of the cellar, take the method of transporting them out of the cellar, in order to prevent the seedlings from losing water, before transportation, it is necessary to take mud-staining measures on the root system of the seedlings, if it is a long-distance transportation, use wet sawdust to moisturize the root system. During transport, the seedlings are covered with a tarpaulin.
8 Track service survey results
From July to August of each year from 2013 to 2019, the user tracking service of purchasing large bell jujube grafting seedlings inside and outside the province was investigated once, mainly to investigate the incidence of frost damage of new seedlings in that year. The survey results show that liaoning, Shandong, Inner Mongolia and other provinces and regions have purchased 520,000 large bell jujube winter cellar grafted seedlings from Chaoyang Longdu Forest Fruit Development Co., Ltd. and found no frost damage phenomenon (Table 3).
Table 3 Application of grafted seedlings in winter cellars of large bell dates
This new cellar technology is also suitable for the storage of other seedlings that are susceptible to frost damage in the nursery, such as flower seedlings or fruit tree seedlings, and it is recommended to vigorously promote and apply them in similar areas.