**1 Scope**
This standard outlines the technical requirements for managing citrus orchards, including the removal (towing) of dense orange trees, pruning large branches, thinning fruit, and increasing the application of organic fertilizers during the cultivation process.
It is specifically designed for high-quality and high-yield citrus production during the peak fruiting period. The guidelines are intended to improve orchard efficiency, fruit quality, and long-term sustainability.
**2 References**
The clauses in the following standards are incorporated into this document and form an integral part of it. At the time of publication, the editions mentioned were valid. All standards may be revised, and users are encouraged to check for the latest versions.
- GB 6868-86: Pruning shears
- GB 7172-86: Hand saw
**3 Definitions**
This standard uses the following definitions:
- **Main branch**: A large branch that originates from the main trunk.
- **Secondary main branch**: A larger branch that branches off from the main or secondary main branch.
- **Lateral branch**: A branch that develops from the main or secondary main branches and bears fruit and supports renewal.
- **Thickness of the green leaf layer**: The thickness of the densest part of the foliage between the lower and upper parts of the canopy.
- **Canopy coverage**: The ratio of the projected crown area to the total garden area.
- **Smear**: To wipe off or cut off buds.
- **Topping**: To remove the young tip of a vegetative shoot.
- **Sparse cut**: To remove excessively dense branches from the base.
- **Sparse branch pruning**: To remove overly dense main branches, minor branches, or larger lateral branches from the base.
- **Leaf punch percentage**: The ratio of the number of leaf punches to the total number of leaves and fruits.
- **Full fruit period**: The stage from high economic stability to the initial decline in production.
**4 Removal of Dense Orange Trees**
**4.1 Target Density**
In hilly areas, the target density is 840 lowland plants per hectare, while in planned dense planting gardens, it should be 630 or more per hectare. When the canopy coverage reaches 75% or higher, dense orange trees should be gradually removed (or thinned).
**4.2 Removal Method**
Depending on the terrain and planting method, use a septum, interlaced, or plum-shaped approach to remove or thin dense trees.
**4.3 Timing**
The best time for removal is from late February to mid-March.
**4.4 Removal Technique**
**4.4.1 Pre-pruning**
Before removal, prune the tree crown appropriately. Remove upward-growing branches and dense middle-upper branches using techniques like plastic surgery. The amount of pruning should be about 1/3 to 1/2 of the total leaf mass.
**4.4.2 Removal Process**
After pruning, dig a circular trench along the drip line of the transplanted tree. Protect horizontal and fibrous roots during excavation. Dig below the root zone, clear subsoil, cut vertical roots, and wrap the roots with mud and cloth.
**4.4.3 Transplanting**
Transplant the tree into a pre-dug hole with sufficient basal fertilizer and 1–1.5 mg of calcium-magnesium-phosphate fertilizer. Unwrap the roots, spread them, fill soil in layers, and compact it. Ensure the graft union remains above ground. Secure the tree with a triangular support and water thoroughly.
**4.4.4 Post-transplant Care**
Within one month after transplanting, water every 5–7 days if sunny. Spray the crown with nutrients or growth regulators every 10–15 days, 2–3 times. Remove all flower buds of the year. Follow general management practices outlined in DB33/T69-93 for citrus vegetative growth.
**4.5 Thinning**
Remove the tree from the base, ensuring no stumps or roots remain.
**4.6 Precautions**
- Trees under 10 years old are suitable for transplanting; older trees are better suited for thinning.
- As planting density increases, transplanting or thinning should be done earlier.
- The remaining canopy after thinning can help open up the canopy of the permanent tree.
**5 Pruning of Dense Branches**
**5.1 Pruning Conditions**
Prune large branches when the canopy becomes dark, dead branches increase, or fruit moves upward, causing overlapping shoots.
**5.2 Timing**
Pruning should occur from late February to mid-March.
**5.3 Pruning Techniques**
**5.3.1 General Round Pruning**
Start by removing the base or problematic upright main branches. After cutting, cover the crown. Remove larger side branches from different directions to create a wavy canopy.
**5.3.2 Planned Pruning for Dense Orchards**
Identify permanent trees and those to be removed. If a planned tree’s branches interfere with the permanent tree, remove the affected main, secondary, or larger lateral branches from the base. Apply the same technique as in 5.3.1.
As the permanent tree grows, continue annual pruning to reduce canopy size. Thin the tree when its yield is less than one-third of the permanent tree’s output.
**5.4 Precautions**
- Prune 1–3 main branches annually. High-yielding or mature trees may require more cuts, while young or low-yield trees need fewer. Annual pruning should account for 10–20% of total leaves.
- Retain buds that can expand the canopy or develop into next year’s branches. Erase the rest.
- Timely remove large branches and sparse branches.
**6 Fruit Thinning**
**6.1 Timing**
Fruit thinning begins after the second physiological drop of fruit, typically completed by early September.
For specific varieties:
- Hu Youpiao, early Wenzhou Mi Mandarin, navel oranges: First thinning at the end of June to early July, second thinning in late August.
**6.2 Amount of Thinning**
Determine the number of retained fruits based on planned yield and grade fruit rate. Use the formula:
C = A × D × A% + B × D × B%
Where:
A = average weight of first-grade fruit, A% = proportion of first-grade fruits
B = average weight of second-grade fruit, B% = proportion of second-grade fruits
C = number of fruits set, D = planned yield per unit area
**6.3 Thinning Methods**
**6.3.1 First Thinning**
Remove small, deformed, or damaged fruits. For Huyou and early harvest mandarins, remove fruits with a diameter less than 3.0 cm.
**6.3.2 Second Thinning**
Continue removing pests, deformed fruits, wind-damaged, sunburned, rough-skinned, or oversized fruits.
**6.4 Precautions**
- Adjust thinning based on orchard conditions, tree age, and canopy size. High-yield varieties may be thinned more. Young or low-yield trees may only remove pests or deformed fruits.
- Follow local guidelines for optimal fruit thinning.
**7 Increasing Organic Fertilizer Application**
**7.1 Target Areas**
Apply organic fertilizer where chemical fertilizers have led to nutrient deficiencies, poor soil structure, or low organic matter content.
**7.2 Organic Fertilizer Usage**
During the fruiting period, apply 35–40% of the total annual fertilizer as organic material. Deep-turn the soil and replace it every 1–2 years.
**7.3 Fertilization Schedule**
- Strong fruit fertilizer: Late June to mid-July
- Fruit fertilizer: Mid-August to mid-September
- Post-harvest fertilizer: One month after citrus harvest
**7.4 Application Methods**
Follow the deep-turning and soil-changing methods described in DB33/T169.3-93.
**7.5 Precautions**
Use fast-acting organic fertilizers such as cooked cake, barium, or bio-organic compounds when applying fruit-setting and strong fruit fertilizers.
Smog Air Pump,Smog Pump,Air Pump For Car,Smog Air Pumps
Suzhou Barjon Auto Parts Co.,Ltd , https://www.cn-barjon.com