Notes on Thinning and Renovation of Densely Planted Apple Orchards
Excessive planting density, deteriorating light conditions in the orchard, outward migration of fruiting positions, declining fruit quality, and falling production efficiency are common problems in apple production in China. When carrying out thinning and renovation of old orchards, the following points should be noted.
1. Keep the best trees. Within an orchard, the fruiting capacity of different individuals varies, both among cultivars and among individual plants. Some plants, due to pest and disease damage, especially after being affected by Valsa canker, have impaired internal transport of substances and reduced fruiting capacity. During thinning and renovation, attention should be paid to keeping the best trees.
2. Thoroughly remove the trees selected for thinning. For the trees designated for thinning, all aboveground and underground branches, trunks, and roots should be completely removed. The branches and trunk on the tree body can first be sawed off, then the main trunk dug out, and the root system fully extracted, to prevent the spread of root rot and protect the healthy growth of the root systems of the retained plants.
3. Backfilling of tree holes. Because nutrients in the tree holes are heavily consumed over the long growth period of the trees and toxic substances accumulate in large amounts, which is very detrimental to fruit tree growth, the opportunity of backfilling can be used to apply large amounts of organic fertilizer or bury weeds in the holes to supplement soil nutrients; fill the holes with mature soil from between the rows to optimize the soil structure within the holes.
4. Strengthen management of the retained plants. In the first 1 to 2 years after thinning, orchard yield declines slightly, and promoting yield recovery is the top priority in the management of thinned orchards. In production, the following work should be emphasized:
1. Strengthen tree management. In the tree management of apple orchards after thinning, the following points should be highlighted:
(1) Play down the concept of tree shape and shift the regulation goal. Thinned and renovated apple orchards should aim to increase yield, improve quality, and boost efficiency, and should not be bound by traditional concepts. With the goal of "having shape without rigidity, being formless without disorder," shape the tree according to the tree itself, and do not overemphasize tree shape. As long as the retained plants have open branch angles, full fruiting branches, a sturdy framework, and drooping fruiting branches, that is a high-yield tree appearance.
(2) Make full use of the branches of the retained plants to increase branch volume in the orchard. When regulating the tree body of thinned and renovated apple orchards, branches should mainly be left unpruned, and as few branches as possible should be removed, or none at all. Because after thinning the plants in the apple orchard, sufficient space is freed up and overall light conditions are optimized, the retained branches can basically receive full sunlight. Long branches should be bent and trained as much as possible to transform them into fruiting branches. Within 1 to 2 years after thinning, restore the branch volume to 70,000 to 80,000 branches per mu to form a new fruiting population.
(3) Strengthen the cultivation of drooping branches. Fruiting on drooping branches conforms to the growth characteristics of apples and favors the accumulation of photosynthetic products. Due to the effect of Earth's gravity, the fruit produced has proper shape and excellent quality. At the same time, after the fruiting branches droop, they can improve the light conditions in the orchard. Therefore, after thinning and renovation, as many drooping branches as possible should be cultivated for fruiting. For branches sprouting from the branch axis, adopt the management measure of leaving them unpruned, unpruned, and unpruned again, cultivate them into robust branch groups, then change their direction by bending, and transform them into drooping fruiting branches. This is the core measure for increasing yield and quality, and it should be highly valued in production.
2. Build up soil fertility. Soil fertility status directly determines apple production efficiency. In apple orchards after thinning and renovation, building up soil fertility should be taken as one of the breakthroughs for improving production efficiency and tackled with full effort. The following measures should be emphasized:
(1) Where farmyard manure is available, apply sufficient farmyard manure. Apple orchards after thinning should ensure an application rate of about 5,000 kg per mu, or 50 to 100 kg of biogas residue per plant. Where farmyard manure is insufficient, apply commercial organic fertilizer and ensure an application rate of about 500 kg per mu to lay a foundation for efficient production.
(2) In areas rich in crop straw, promote the straw mulching method. This is an effective measure for increasing soil organic matter. Cover the tree basin, tree rows, or the entire orchard with crop straw. After 2 to 3 years of decomposition, plow it into the soil, which can greatly increase soil organic matter content and is very beneficial to apple production.
(3) Where irrigation conditions are available, carry out sod culture. This can be done by interplanting shallow-rooted, high-growth grasses such as clover and ryegrass between the rows, and mowing during the growing season to cover the tree basin or directly turn them under, so as to increase soil organic matter content.
3. Strengthen moisture conservation and prevent tree vigor decline. In northern China, low precipitation and drought-induced moisture deficiency are among the main factors causing tree vigor decline and affecting yield and quality. Apple orchards after thinning should strengthen moisture conservation measures. Through measures such as orchard grass mulching and film mulching, improve soil water use efficiency and ensure robust tree growth.
4. Protect leaves and increase the accumulation of photosynthetic products. Strengthen the control of pests and diseases that harm leaves, ensure leaf integrity, and improve the ability to produce photosynthetic products. In autumn, apply foliar fertilizer to extend the growth time of functional leaves, increase the accumulation of photosynthetic products, and increase tree nutrition.
Wang Tianli, Forestry Bureau of Jingning County, Gansu Province