1. Nutritional characteristics and fertilization techniques

（1） Fertility and Nutritional Characteristics

Apples and pears are both benevolent fruit trees, with similar growth habits and fertilization techniques. The root system is mainly distributed within the corresponding range of the tree crown, 1&dash away from the main trunk; The root volume of 1.5 meters accounts for about 75% -80% of the total root volume, and the vertical distribution can reach 3— 4 meters, mostly concentrated in the 0-40 centimeter soil layer. The root system of apples begins to move above 0 ℃, and at 3 ℃ -; Start growing at 4 ℃, 7 ℃‐ The growth is most vigorous at 20 ℃; Pear tree root system at 5 ℃‐ Start activity at 7 ℃, 15 ℃‐ It grows vigorously at 20 ℃. When the soil temperature exceeds 30 ℃, the root systems of apples and pears almost stop growing. Generally, the growth of the root system is 20% earlier than the growth of the branches; 25 days.

Both apples and pears require slightly acidic to neutral soil with a pH value of 5.5-; 6.7 Growing well, when the pH value is greater than 8.0, apples will lose their green color due to iron deficiency induction. Pear trees do not have strict requirements for soil acidity and alkalinity, and can still grow normally at a pH value of around 8.0. Apples and pears have different nutrient requirements. Calculated based on the production of 1000 kilograms of fruit, adult apples absorb 3.0 kilograms of nitrogen (N), 0.8 kilograms of phosphorus (P2O5), and 3.2 kilograms of potassium (K2O) in a ratio of 1:0.27:1.07; 11 year old pears absorb 4.3 kilograms of nitrogen (N), 1.6 kilograms of phosphorus (P2O5), and 4.1 kilograms of potassium (K2O) in a ratio of 1: 0.37-0.95. Pears absorb more nitrogen, phosphorus, and potassium than apples.

Apples and pears have similar nutrient absorption patterns at different stages of growth. From germination to flowering, it has been determined that the nutrient and reproductive organs such as flowers, new shoots, and young leaves have high levels of nitrogen, phosphorus, and potassium, especially nitrogen, indicating an urgent need for nutrients during germination and flowering. But this period mainly utilizes the nutrients stored in the tree body from the previous year, and does not absorb much from the soil. Entering the period of vigorous growth of new shoots, the tree has a large amount of growth, which is the period of maximum fertilizer absorption. Among them, nitrogen absorption is the highest, followed by potassium, and phosphorus is relatively low. Entering the stage of fruit development and flower bud differentiation, the fruit is rapidly expanding, and at the same time, the differentiation of new flower buds also requires a greater supply of nutrients. During this period, nutrient absorption is in the order of potassium>nitrogen>phosphorus. Fruit trees are harvested until the leaf shedding period, during which nutrient reflux is the main process to store organic matter for the following year. The tree still needs to absorb some nutrients, but the amount absorbed is significantly reduced.

（2） Fertilization technology

1. Base fertilizer. Organic fertilizers should be the main source, with chemical fertilizers as a supplement. Generally, mature organic fertilizer is applied to each adult tree at a rate of 35-50%; 50 kilograms, combined with the application of urea 0.5– 1 kilogram, superphosphate 1‐ 2 kilograms or compound fertilizer (2:2:1 type) 1— 1.5 kilograms.

Base fertilizer can be applied in autumn, winter, and spring, and it is better to apply it immediately after the autumn fruit harvest. Applying base fertilizer in autumn coincides with the second or third growth peak of fruit tree roots. The damaged roots caused by fertilization are easy to heal, breaking some small roots and playing a role in root pruning, which can promote new roots. At this point, the newly formed organs in the aboveground part of fruit trees have gradually stopped growing, and the nutrients they absorb are mainly accumulated and stored, which can improve the nutritional level and cell fluid concentration of the tree, and facilitate overwintering and early growth of fruit tree sprouts, flowers, and new shoots in the following year. Fertilization in winter, with low temperatures, not only makes it difficult for damaged roots to heal and new roots to form, but also reduces nutrient absorption, which is unfavorable for the growth of fruit trees in the coming year. Applying base fertilizer in spring can slow down its effectiveness and often fail to meet the growth needs of early spring. It can also lead to the regrowth of branches in later stages, affecting flower bud differentiation and fruit development. Therefore, the base fertilizer for apples and pears should be applied early in autumn.

2. Topdressing. Also known as fertilization. The effectiveness of base fertilizer is stable and slow. When fruit trees urgently need it, it must be replenished in a timely manner to meet their growth and development needs. Topdressing is not only necessary for strong trees, high yields, and high quality in the current year, but also lays the foundation for the growth and results of the following year. It is an indispensable part of fruit tree fertilization. The number of topdressing cycles is generally 2— Four times, sandy soil should be fertilized in small amounts multiple times, and young trees or trees with weak growth during the peak fruiting period should also be fertilized multiple times. The suitable period for topdressing is as follows:

① Fertilization before flowering: Sprouting and flowering require a large amount of nutrients, but in early spring, the temperature is low and the tree's absorption capacity is weak, mainly consuming the nutrients stored in the tree. The follow-up application during this period should be determined based on the fertilization situation before the new year and the growth of the tree. If the base fertilizer is sufficient before the new year (autumn) and the tree growth is strong, it can be skipped or postponed until after flowering. For weak trees, old trees, and trees with excessive fruiting, it is important to pay attention to this fertilization to promote neat sprouting and flowering, and improve fruit setting rate. Generally, high concentration compound fertilizer (2:1:1 type) is applied to each plant; 1.5 kilograms. If no base fertilizer has been applied or the amount of base fertilizer is insufficient before the new year (autumn), it is advisable to apply organic fertilizer in combination with chemical fertilizer.

② Fertilization after flowering: Apply fertilizer during the post flowering and fruiting period. At this time, the growth of young fruits and new shoots accelerates, requiring more nutrient supplementation. Generally, high concentration, high nitrogen, and high potassium compound fertilizers (2:1:2 type) are applied, with each plant being treated at a rate of 1 to 2 hours; 1.5 kilograms. This time, the fertilizer and pre flowering fertilizer can complement each other. If the pre flowering fertilizer is sufficient and the tree is strong, it can also be applied less or not at all.

③ Topdressing during the period of fruit enlargement and flower bud differentiation: During this period, some new shoots stop growing and new flower buds begin to differentiate. Topdressing this time is beneficial for fruit enlargement and flower bud differentiation, which can ensure high quality and yield in the current year, lay the foundation for the next year's results, and also have an effect on overcoming the problem of aging. This period requires a significant supply of potassium nutrients, and it is advisable to use high potassium and low phosphorus compound fertilizers, with each plant applying about 2 kilograms.

④ Fertilization in the late stage of fruit growth: This fertilization mainly solves the contradiction between the need for fertilizer for fruit development and flower bud differentiation. This fertilizer is particularly important for late maturing varieties. According to research, if the content of potassium and carbon compounds in the fruit is high, the fruit will be well colored. Therefore, during this period of topdressing, attention should also be paid to increasing the application of potassium fertilizer, with each plant applying about 1 kilogram of high potassium compound fertilizer. It is also applied in combination with base fertilizers in production.

3. Fertilization outside the roots: mainly to supplement the deficiency of moderate and trace nutrients. When lacking calcium, 0.3% can be sprayed during the fruit swelling period; A 0.5% calcium nitrate solution, applied continuously for 4 times, can effectively prevent and treat apple bitter acne and pear cork plug disease. If there is a zinc deficiency, about 3 weeks after flowering, when the tree shows symptoms of leaf disease, spray 0.2% zinc sulfate and 3% -; A 5% urea mixture can restore the diseased branches to normal.

2. Symptoms of nutrient deficiency

When nitrogen is deficient, the lower leaves of the branches show uniform yellowing and develop towards the upper leaves. New leaves are small and thin, appearing light green or purple, while older leaves are orange, red or purple, and are prone to early shedding. The branches are thin and weak.
When phosphorus is deficient: new leaves are dark green, old leaves are bronze colored, purple brown spots or patches appear on the leaf surface near the edge, branches are thin and weak, and branches that grow faster in spring and summer appear purple red. When apples are deficient in phosphorus, the leaf petioles and dorsal veins of the leaves turn purple red.
When potassium is deficient: the leaf edges at the base and middle of the branches turn green and yellow, and the leaves shrink. In severe cases, the leaves become brown and burnt, making them difficult to fall off. Poor growth of branches.
When lacking calcium: light green or brownish yellow fading spots appear on the top of the new shoots and young leaves, which turn into brown or green brown withered after 2-3 days. The leaf tips and edges curl downwards.
When magnesium is deficient: the veins lose their green color, while the veins remain green. Leaves curl and fall off easily, and new shoots and tender branches are relatively slender and easy to bend. The leaves are in the shape of; Rib shaped "loses its green color.
When zinc is deficient: the leaves are narrower than normal, hard and brittle in texture, and the leaf edges curl up without stretching. Commonly known as“ Small leaf disease. The loss of green between leaf veins results in yellow patches.
When lacking boron: the whole plant has top withering and clumping phenomena, with new shoots dying from the top downwards. Many fine branches are extracted from the shoots under the dead branches, and the internodes are short. On the internodes, many clustered small leaves are produced, and the leaves are narrow and thick.
When iron deficiency occurs: Yellowleaf disease occurs, the leaf flesh loses green and turns yellow, and the leaf surface appears as a green net pattern, smaller than normal leaves. In severe cases, the entire leaf appears yellow white.