**1. Scope**
This standard outlines the technical requirements for managing dense orange trees during citrus cultivation, including tree removal (towing), pruning of large branches, fruit thinning, and increasing organic fertilizer application. It is specifically designed for high-quality and high-yield citrus production during the peak fruiting period.
**2. References**
The clauses specified in the following standards are incorporated into this document and form an integral part of its provisions. At the time of publication, the editions listed were valid. All references may be revised, and users are encouraged to check for the latest versions.
- GB6868-86: Pruning shears
- GB7172-86: 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 grows out from the main or secondary main branch.
- **Lateral branch**: A branch that develops from the main or secondary main branch and bears fruits and supports renewal.
- **Green leaf layer thickness**: The thickness of the densest part of the foliage between the lower and upper parts of the canopy.
- **Canopy coverage**: The ratio of the crown's projected area to the total garden area.
- **Smear**: To remove or cut off buds.
- **Topping**: To trim the young portion of a vegetative shoot.
- **Sparse cutting**: To remove excessively dense branches at their base.
- **Sparse branch pruning**: To remove dense main, minor, or side branches from the base.
- **Leaf punch percentage**: The proportion of leaf punches relative to the total number of leaves and fruits.
- **Full fruit period**: The stage of high economic stability until the initial decline in yield.
**4. Sparse (Cutting) Dense Orange Trees**
4.1 **Target Density**: In hilly areas, aim for 840 lowland plants per hectare, and in planned dense plantings, maintain 630 or more per hectare. When canopy coverage reaches 75% or more, dense trees should be gradually removed or thinned.
4.2 **Method**: Depending on terrain and planting style, use a septum, interlaced, or plum-shaped method for removal or thinning.
4.3 **Timing**: From late February to mid-March.
4.4 **Techniques**:
- **Pre-pruning**: Trim the tree crown before removal, removing upward-growing branches and dense upper and middle branches. Prune about 1/3 to 1/2 of the crown’s leaves.
- **Removal Method**: Dig a ring groove along the drip line after pruning. Protect horizontal and fibrous roots while digging. Cut vertical roots and wrap the root system with mud and straw.
- **Transplanting**: Transport the tree to a pre-dug hole with sufficient base fertilizer and 1–1.5 mg of calcium, magnesium, and phosphate fertilizer. Unwrap the roots, spread them, and backfill soil carefully, ensuring the graft union remains exposed. Secure the tree with a triangular support and water thoroughly.
4.5 **Aftercare**:
- Water every 5–7 days if sunny within one month post-transplant.
- Spray nutrient solutions or growth regulators every 10–15 days for 2–3 times.
- Remove all flower buds of the year.
- Follow general management practices for citrus vegetative growth as outlined in DB33/T69-93.
4.6 **Thinning**: Saw the tree from the base, leaving no stumps or roots.
4.7 **Precautions**:
- Transplanting is suitable for trees under 10 years old; thinning is generally used for trees over 10 years.
- Adjust transplanting or thinning timing based on increased planting density.
- Leave some canopy after thinning to help open up space for permanent trees.
**5. Sparse Branch Pruning**
5.1 **When to Prune**: Prune large branches when the canopy becomes dark, dead branches increase, or fruit moves upward.
5.2 **Timing**: From late February to mid-March.
5.3 **Techniques**:
- **Ordinary Round Trim**: Start by removing upright or dominant branches. After cutting, cover the crown and remove side branches to create a wavy canopy.
- **Planned Pruning for Dense Plantations**: Identify permanent trees and those to be removed. If a planned tree overlaps with a permanent one, remove the interfering branches from the base.
- **Ongoing Management**: As the permanent tree expands, prune annually to reduce canopy size. Thin when the planned tree produces less than 1/3 of the permanent tree’s output.
5.4 **Precautions**:
- Prune 1–3 main branches annually, depending on tree age and health.
- Retain buds that can help expand the canopy or form next year’s branches.
- Remove large branches and sparse branches promptly.
**6. Fruit Thinning**
6.1 **Timing**: Begin after the second physiological fruit drop, typically in early September.
- For Hu Youpiao, early-maturing Wenzhou Mi Mandarin, and navel oranges: First thinning from late June to early July, second thinning in late August.
6.2 **Amount of Thinning**:
- Calculate retained fruit using:
$ C = A \times D \times A\% + B \times D \times B\% $
Where:
- $ A $: Average weight of grade A fruit
- $ A\% $: Proportion of grade A fruit
- $ B $: Average weight of grade B fruit
- $ B\% $: Proportion of grade B fruit
- $ C $: Total fruit set
- $ D $: Target yield per unit area
- Use leaf-to-fruit ratios:
- Main varieties: 80–100:1
- Hu Youya: 60–80:1
- Precocious Satsuma Mandarin: 30–35:1
- Late Wenzhou Mandarin: 25–30:1
- Navel Orange: 70–90:1
6.3 **Methods**:
- First thinning: Remove small, deformed, or damaged fruits (diameter < 2.5 cm for Huyou and early harvest mandarins).
- Second thinning: Remove pests, malformed, wind-damaged, sunburned, rough-skinned, or oversized fruits.
6.4 **Precautions**:
- Adjust thinning based on orchard conditions, tree age, and canopy size.
- Young or low-yield trees may only need to remove pests and malformed fruits.
**7. Increasing Organic Fertilizer**
7.1 **Targets**: Apply organic fertilizers to address malnutrition, poor soil quality, and low organic matter content.
7.2 **Application Rate**: During the fruiting period, apply 35–40% of annual fertilizer as organic, and perform deep turning and soil replacement 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 **Methods**: Follow DB33/T169.3-93 for fertilization, deep-turning, and soil-changing.
7.5 **Precautions**: Use fast-acting organic fertilizers like cooked cake, bio-organic compound, or manure-based fertilizers when applying fruit fertilizer.
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