A Training System of Pear Trees for Simplified High-density Cultivation

Jintao XU Longfei LI Lijuan GAO Minghui JI Yong GUO Shujun ZHAO Hai’e ZHANG Baofeng HAO

Abstract In view of the deficiencies of training technologies during constructing pear orchards by modern simplified dense-planting cultivation with ordinary pear seedlings widely used in production， a simple and easy-to-operate training method was proposed， mainly including constructing fence nets， determining low main trunks， leaving buds at the northwest position， multiple bud removal， winding and notching， simplified branch supporting， and simplified branch pulling.

Key words Pear tree; High-density cultivation; Simplified pruning techniques; Training system

Received： September 3， 2021   Accepted： November 5， 2021

Supported by Innovation Engineering Project of Hebei Academy of Agriculture and Forestry Sciences （2022KJCXZX-CGS-7）; Key R&D Program of Hebei Province （21326308D-1-2）; China Agriculture Research System of MOF and MARA （CARS-28-27）.

Jintao XU （1984-）， male， P. R. China， master， associate professor， devoted to research about research and extension of fruit tree cultivation technology.

*Corresponding author.

Simplified dense-planting cultivation mode is the current development direction of China’s pear industry， and all parts of the country are in the trial and exploration stage[1]. At present， ordinary seedlings and conventional training techniques are still widely used in pear production in China to build orchards. Although the concept of simplified dense-planting cultivation has been deeply rooted， the quality of seedlings and supporting training technologies cannot meet the technical requirements of modern pear production adopting high-density and ultra-high-density cultivation， resulting in late formation of pear orchards， difficult crown control， and time-consuming and labor-intensive management， so large crowns are formed in a short period of time and cross between trees obviously， and inappropriate cultivation density is formed. Consequently， thick and long branches should be removed year after year， wasting a lot of tree nutrition and manpower， and in a severe case， trees are dug out， ruining the orchards.

Therefore， after many years of practice， in view of the deficiencies in training technologies during constructing orchards with ordinary pear seedlings widely used in production， it is necessary to propose a training method that is simple to implement， easy to operate， and suitable for modern dense-planting and labor-saving cultivation technologies[2-4].

Technical Points

Creating a mesh fence

Creating a supporting frame

Along the pear tree planting rows， one hot-dip galvanized pipe is evenly erected every 10 m. The embedded end of each hot-dip galvanized pipe is poured with cement， and the aboveground part is 3.0 m high. Before pouring， the aboveground part of the hot-dip galvanized pipe shall be drilled at a distance of 0.4， 0.9， 1.5， 2.0 m from the ground， respectively. The holes should be formed with a diameter ensuring that a 1.5-4.0 mm steel wire can pass through smoothly， and the hole diameter should not be too large， and can be adjusted appropriately according to the actual situation.

Creating a net

Steel wires are penetrated through the small holes of the galvanized pipes， and they are converged at the ground， fixed with ground anchors， and tightened with a wire tensioner. The anchor depth is 80 cm， and the bevel angle is 30°-40°， which should not be too large.

Pruning in the first year

Planting seedlings

Seedlings with a height greater than 1.2 m and a thickness greater than 1.0 cm having full buds and strong roots are selected， for plantation. The planting row spacing is 3.5-4.0 m， and the plant spacing is 0.8-1.0 m. Seedlings are planted along the constructed fence-type nets， watered immediately after planting， and fixed vertically on the nets with tie cards or sack thread. Or the trees can be fixed after determining main trucks.

Determining main trucks

The main trunks of trees are determined within 1-2 d after planting， and the heights of the determined trucks should not be higher than 50 cm. When determining the main trunk of a tree， a full bud is found， and the height of the main trunk is determined 1-2 cm above the bud. It is necessary to choose full buds in the northwest.

Removing buds multiple times

After buds germinate， 2 buds under the cut are remained， and other buds are removed immediately. If the buds are not removed at one time， they can be removed in time throughout the growing season. Among the two preserved buds， one of them is a sacrificial bud. After the other is alive， the better bud is retained， and the abandoned one is removed immediately.

Binding in time

With the growth of buds， new shoots continue to grow taller， and the lignified part of the new shoots should be tied vertically on the net surface in time to prevent the branches from bending， so as to ensure the apical dominance of the new shoots.

Pruning in the second year

Bud-notching

For the main trunks cultivated in the first year， the method of notching buds is adopted to promote branching of the central trunks. When the buds are notched， the buds within 20 cm from the top are not notched， and the rest of buds are cut certainly. The time for notching buds is about 1 week before the buds germinate， and is completed within 1 week after the buds germinate at the latest. The effect of notching buds is good at this stage. The method of notched buds is cutting 1/2 to 3/4 circles lightly around the buds to the xylem using a saw blade at 0.5-1.0 cm directly above the buds.

Opening the base angle

When the new shoots on the central trunks grow to 15-20 cm， two-pointed toothpicks （length 55-70 mm， diameter 1.0-1.2 mm） are used to open the base angle， which is appropriate to be 60°-80°.

Opening the waist angle

As the new shoots on central trunks continue to grow， the new shoots appear to grow upwards. At this time， the waist angle should be opened to inhibit the growth of new shoots and promote the formation of flower buds.

① Material preparation： Bamboo skewers with a length of 35-40 cm and a diameter of 4-5 mm having one sharp end are selected. They are sold in the market and mostly used for candied haws， barbecue and other purposes， or other specifications desired can also be used. Fruit tree pruning shears are prepared.

② Simplified method of opening the waist angle： When the new shoots grow to 30-35 cm， the above bamboo skewers are inserted at the base of appropriate branches of the upper part of the central trunks from the phloem with their sharp ends into the xylem， to increase stability， and the round ends， according to the required length， are cut with the pruning shears into a bevel and placed in a suitable position of the new shoots， so that the waist angle of the new shoots can reach 70°-80°. The waist angle of the new shoots at the lower part of the central trunks can be appropriately larger， reaching 80°-90°.

In practice， according to the required length， the bamboo skewers can be cut to make the cross sections at both ends and the bamboo sticks form approximately isosceles trapezoids， and then， one end is inserted into a central truck， and the other end is inserted into an appropriate part of the branch.

Pulling branches

Small quantities of branches at the base of which the waist angle cannot be opened by supporting branches are subjected to pulling treatment.

① Material preparation： Bamboo skewers are the same as those under "Opening the waist angle". Sack thread and scissors are also prepared.

② Simplified branch pulling method： Branches are positioned. According to the requirements of the spatial distribution of the angle and orientation of branches， a branch is pressed or rotated and softened to find the balance point of branch’s tensile force on the branch， that is， the branch can maintain the required angle and orientation when it is stressed at this point.

Branch pulling： The above bamboo sticks are used as ground prongs. The insertion positions of the prongs are set according to the angle and orientation of the branches. The sharp end is inserted into the soil with bare hands. The insertion direction and the direction of the pulling force should be different， and the sack thread is used to connect the balance points of the branches with the prongs.

Thinning branches

For varieties with strong growth potential， branches can be retained in the early stage to disperse the tree vigor. According to the tree shape requirements， 30 to 35 branches can be retained on the whole tree retains evenly， and the remaining branches are thinned out from the base. For varieties with weaker growth potential， thinning can be started after buds on the central trunks germinate to thin out too many branches， leaving 30 to 35 branches in the whole tree. When thinning， attention should be paid to thinning out strong and prosperous branches and retaining moderate and weak branches.

Promoting flower bud formation

Most varieties of pear trees are easy to bloom. For varieties that are not easy to flower， 200 times PBO solution is sprayed on the lower branches of trees 1 to 2 times before the shoots stop growing in spring to promote stopping of branch growth and formation of flower buds.

Training in the third year

Management of the extension branches of central trunks

For the extension branches of central trunks of which the branch number and plant height are less than required， the operation of the previous year is repeated， so that the total number of remaining branches of the whole tree reaches 35-40.

Management of side branches

The side branches that are more than 1/3 of the thickness of the central trunks are thinned out， leaving the prongs， and re-branching is allowed depending on hidden buds. For the remaining side branches， branches on the back and strong branches are thinned out according to removing the strong and leaving the weak. At the same time， strong competitive branches are thinned out， and the side branches are kept uniaxial without extension.

Through the above 2-3 years of cultivation， the plant height of the above-mentioned shaped trees can be controlled at about 3.5-3.8 m， 3.2-3.5 m in cold areas， the stem height is 50-60 cm， the crown width is 0.8-1.2 m， and there are 35 to 40 fruiting branch groups on the central trunks.

Precautions and beneficial effects

① Attention should be paid to constructing fence nets， determining low main trunks， leaving buds at the northwest position， multiple bud removal， and timely binding， to ensure the advantages of the central trunks and help the central trunks reach the ideal height as soon as possible during the first year of training. At the same time， it can ensure that the new shoots do not appear partial crown and prosperous growth after bud notching in the second year.

② The method of notching every bud is adopted to promote the branching of the central trunks， which is conducive to controlling branching in the early stage， reducing the crown width， and removing redundant branches in the later stage， providing more options for retaining branches.

③ The bud notching method of "winding and notching" is adopted. It effectively utilizes saw blades’ dark and shallow serrations， which do not completely cut off the upper phloem of the notched buds under the technical characteristics of "winding and notching"， so the cuts can heal in the later stage， and the wounds are not too deep， and will not cause the condition of unsatisfactory branching effects due to water loss. The technical feature of "winding and notching" is more suitable for the treatment of a large number of buds that need to be notched on central trunks to promote branching. In spring dry areas， no casing is needed after "winding and notching"， which eliminates the casing work and solves the problem of serious sunburn after casing in some areas.

④ The use of long bamboo sticks for simplified angle opening and simplified branch pulling effectively solves the inconvenience caused by mechanized operations of orchards adopting the simplified dense-planting cultivation mode， such as the conventional ground prong branching pulling， or pulling by hanging heavy objects， or drawing wires in the row direction， thus significantly improving the work efficiency. After the rapid and timely branch pulling treatment， flower buds can be formed in the second year， and crowns can be pressed by the fruit， eliminating the need to pull branches. The ground prongs are small and do not need to be collected manually， and are directly used as a fertilizer. The sack thread is directly broken， and there is no need to untie the rope. In addition， the position of the ground prongs is flexible. Generally， they are set within rows， and are minimally invasive to the ground cloth， so they can be kept away from the dropper system， and the problem of inconvenience caused by conventional technologies to mechanized operation of orchards can be solved.

References

[1] XU JT， ZHAO HY， LI YH， et al. Effect of trimming pattern on growth and light utilization of ‘Huang-guan’ （Pyrus bretschneideri Rehd.） seedlings[J]. Journal of Northwest A&F University： Natural Science Edition， 2015， 4（43）： 85-90. （in Chinese）

[2] HAO BF， XU JT， LI LF， et al. A training method for slender and upright trunks of pear trees： China， ZL 201710034846.0[P]. 2020-03-17. （in Chinese）

[3] HAO BF， XU JT， LI LF， et al. A method of opening the waist angle during the training process of young pear trees： China， ZL201710034835.2 [P]. 2021-04-27. （in Chinese）

[4] HAO BF， XU JT， GAO LJ， et al. A method of pulling branches during the training process of young pear trees： China， 201711189400.1[P]. 2018-04-13. （in Chinese）

Editor： Yingzhi GUANG  Proofreader： Xinxiu ZHU