Nitrogen plays a very important role in the growth and development of apple trees. Nitrogen has long been considered an important nutrient during the growth and development of apples. The effects of nitrogen on vegetative growth, flowering, fruit set, yield formation, quality and postharvest physiology have been extensively confirmed. The results of many experimental studies and production applications show that the rational use of nitrogen fertilizer can effectively enhance the storage level of trees, increase the fruit setting rate, improve or enhance the quality of fruits, and enhance tree resistance. Excessive or improper application of nitrogen fertilizer can cause adverse effects such as decreased fruit quality and prolonged tree length. The laws of absorption, utilization, utilization and redistribution of nitrogen in trees are also affected by other factors such as hormones.
First, the way apple trees absorb nitrogen
The roots of apple trees absorb inorganic nitrogen and organic nitrogen from the soil. To a large extent, the absorption of nitrogen depends on the appearance of the leaves. There are two main forms of inorganic nitrogen absorbed by the roots from the soil, namely NO3-, NH4+. Although some N2 is present in the soil, the roots of the fruit trees cannot be absorbed and utilized because they have no nitrogen fixation ability. Apple roots are able to absorb organic nitrogen from the soil. Ozerol and Titus (1968) and Shim et al. (1973b) found that apple roots can easily absorb 14C of urea and can be synthesized with sugars, organic acids and amino acids. After urea was applied to the roots, 14C was detected from amino acids and sugars in 2 hours (Shim et al. 1973b).
The application of nitrogen fertilizer outside the root has a more significant effect. Yang Xinghong et al. studied the absorption of 15N-urea in apples (Guoguang, Fuji, and Yanqing) before germination in early spring and the absorption and mobilization characteristics after germination. The results showed that the apple branches had a certain absorption capacity for 15N-urea before germination; with the 15N-urea absorbed by germination, spreading leaves and branches moving to the new organs, it has the characteristics of storage nutrition. The application of nitrogen fertilizer outside the root of apple before germination can improve the quality of the leaves. The results of other studies have shown that nitrogen nutrition outside the roots of fruit trees, including nitrogen absorbed by shoots, can improve leaf quality and increase photosynthesis.
Wang Zhongying et al. studied the changes of nitrogen content in apple trees of dwarf anvil. The results showed that the nitrogen content of roots in the early spring buds of the dwarf roots was low, which limited the nitrogen requirement of roots and shoots. Therefore, the dwarf anvil apple tree should pay special attention to the root-extracting nitrogen in the early growth stage to supplement the lack of root absorption.
In the fruit-effect study of applying nitrogen fertilizer outside the flowering roots, after spraying 0.3% urea on the foliar surface, it had a good effect on increasing the fruit setting rate.
The late autumn leaves are topdressed with high concentration of urea, which has a very beneficial effect on the growth and development of fruit trees. After fruit harvesting and 4~2 weeks before defoliation, 4%-5% urea was sprayed on the leaves, which directly affected the growth and development of the tree, and the number of flowering, fruit and short leaf area increased.
Second, the relationship between nitrogen and phosphorus, potassium, etc.
In apple orchard production management, the application of nitrogen fertilizer to apple trees is usually carried out simultaneously with the application of phosphorus and potassium fertilizers. However, the amount of nitrogen fertilizer required is different in the growing season. Wang Jikui and others believe that apple-specific fertilizer is superior to other organic fertilizers in promoting fruit setting, increasing fruit weight, increasing yield and improving quality.
Applying organic biological nitrogen and phosphorus fertilizer on apple trees can significantly improve the tree potential and increase the fruit setting rate, quality and yield. The amount of nitrogen fertilizer applied can have different effects on apple growth and fruit quality. In the study of nitrogen application rate of different tree potentials, Zhang Shaoling applied 0.5, 15kg urea per 666.6 m2 according to the strong, medium and weak tree potential, and applied it on April 25th. The results showed that the difference was that the amount of nitrogen applied had a significant effect on the sugar content of the fruit and the proportion of green fruit. The more nitrogen fertilizer is applied, the higher the proportion of green fruit and the worse the fruit quality. In determining the amount of fertilization, the ratio of nitrogen to potassium should be adjusted according to the strength of the tree, so as to control the growth of new shoots and alleviate the tree potential, which is both high-yield and high-quality.
First, the way apple trees absorb nitrogen
The roots of apple trees absorb inorganic nitrogen and organic nitrogen from the soil. To a large extent, the absorption of nitrogen depends on the appearance of the leaves. There are two main forms of inorganic nitrogen absorbed by the roots from the soil, namely NO3-, NH4+. Although some N2 is present in the soil, the roots of the fruit trees cannot be absorbed and utilized because they have no nitrogen fixation ability. Apple roots are able to absorb organic nitrogen from the soil. Ozerol and Titus (1968) and Shim et al. (1973b) found that apple roots can easily absorb 14C of urea and can be synthesized with sugars, organic acids and amino acids. After urea was applied to the roots, 14C was detected from amino acids and sugars in 2 hours (Shim et al. 1973b).
The application of nitrogen fertilizer outside the root has a more significant effect. Yang Xinghong et al. studied the absorption of 15N-urea in apples (Guoguang, Fuji, and Yanqing) before germination in early spring and the absorption and mobilization characteristics after germination. The results showed that the apple branches had a certain absorption capacity for 15N-urea before germination; with the 15N-urea absorbed by germination, spreading leaves and branches moving to the new organs, it has the characteristics of storage nutrition. The application of nitrogen fertilizer outside the root of apple before germination can improve the quality of the leaves. The results of other studies have shown that nitrogen nutrition outside the roots of fruit trees, including nitrogen absorbed by shoots, can improve leaf quality and increase photosynthesis.
Wang Zhongying et al. studied the changes of nitrogen content in apple trees of dwarf anvil. The results showed that the nitrogen content of roots in the early spring buds of the dwarf roots was low, which limited the nitrogen requirement of roots and shoots. Therefore, the dwarf anvil apple tree should pay special attention to the root-extracting nitrogen in the early growth stage to supplement the lack of root absorption.
In the fruit-effect study of applying nitrogen fertilizer outside the flowering roots, after spraying 0.3% urea on the foliar surface, it had a good effect on increasing the fruit setting rate.
The late autumn leaves are topdressed with high concentration of urea, which has a very beneficial effect on the growth and development of fruit trees. After fruit harvesting and 4~2 weeks before defoliation, 4%-5% urea was sprayed on the leaves, which directly affected the growth and development of the tree, and the number of flowering, fruit and short leaf area increased.
Second, the relationship between nitrogen and phosphorus, potassium, etc.
In apple orchard production management, the application of nitrogen fertilizer to apple trees is usually carried out simultaneously with the application of phosphorus and potassium fertilizers. However, the amount of nitrogen fertilizer required is different in the growing season. Wang Jikui and others believe that apple-specific fertilizer is superior to other organic fertilizers in promoting fruit setting, increasing fruit weight, increasing yield and improving quality.
Applying organic biological nitrogen and phosphorus fertilizer on apple trees can significantly improve the tree potential and increase the fruit setting rate, quality and yield. The amount of nitrogen fertilizer applied can have different effects on apple growth and fruit quality. In the study of nitrogen application rate of different tree potentials, Zhang Shaoling applied 0.5, 15kg urea per 666.6 m2 according to the strong, medium and weak tree potential, and applied it on April 25th. The results showed that the difference was that the amount of nitrogen applied had a significant effect on the sugar content of the fruit and the proportion of green fruit. The more nitrogen fertilizer is applied, the higher the proportion of green fruit and the worse the fruit quality. In determining the amount of fertilization, the ratio of nitrogen to potassium should be adjusted according to the strength of the tree, so as to control the growth of new shoots and alleviate the tree potential, which is both high-yield and high-quality.
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