What nutrients does a walnut tree need for growth and development?

  The growth and development of fruit trees require two major categories of nutrients: one is organic nutrition, including amino acids, proteins, sugars and phospholipids, etc., accounting for 90%-95% of the total dry matter of the tree, all of which are directly or indirectly synthesized by photosynthesis, which shows that photosynthesis is the basis for the formation of fruit tree yield; the other is inorganic nutrition, namely mineral nutrient elements, which are mainly absorbed from the soil by the root system, accounting for 5%-10% of the total dry matter of the tree. These two categories of nutrients are interdependent and mutually transformative, and both play a very important role in the growth and development of fruit trees.

  The essential mineral elements for fruit trees include nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), iron (Fe), boron (B), zinc (Zn), copper (Cu), manganese (Mn), molybdenum (Mo), chlorine (Cl), etc. Among them, nitrogen, phosphorus, potassium, calcium and magnesium are needed in relatively large amounts, with their content levels in the plant expressed as a percentage, and are called "macroelements". Iron, manganese, copper, zinc and boron are needed in relatively small amounts, with their content levels in the plant often expressed in parts per million, and are called "microelements". Although the demand of fruit trees for various mineral elements varies greatly, each element has its own role and is indispensable. Otherwise, it will affect the growth and development of fruit trees and show corresponding symptoms. In addition, there are also synergistic or antagonistic effects among the elements. Synergistic effect means that the presence of a certain element can promote the absorption of one or more other elements by the root system, that is, the combined application of two elements will have a better effect. Antagonistic effect means that the excessive presence of a certain element will inhibit the absorption of one or more other elements by the root system. Therefore, when fertilizing fruit trees, attention should be paid to the proportional relationship among various nutrient elements, and improper application rates will also affect the fertilization effect. In the annual cycle of growth and development of walnut trees, it can be divided into two different nutritional stages: one dominated by the use of stored nutrients in the tree, and one dominated by the use of nutrients synthesized in the current year.

  The first stage is the nutritional stage dominated by the use of stored nutrients in the tree. In the early stage of growth and development of the walnut tree, namely the growth and development processes of sprouting, shoot growth, leaf expansion and flowering and fruit setting, young fruit development, flower bud differentiation, and root growth, all are completed by using the stored nutrients of the tree. If the stored nutrients are sufficient, then sprouting is early, leaf expansion is uniform, new shoots grow rapidly, the fruit setting rate is high, and the quality of flower bud differentiation is high. At the same time, when the stored nutrients are sufficient, the nutrient transformation period begins late and ends early, which can lay the foundation for high yield and high quality. Since the nutrient source for the spring growth and development of walnut trees is mainly the nutrients stored and accumulated in the previous autumn, strengthening autumn management and improving the level of stored nutrients is the basic guarantee for achieving high yield and high quality.

  The second stage is the nutritional stage dominated by the use of nutrients synthesized in the current year. As the rapid growth period of walnut spring shoots ends, the stored nutrients in the tree are exhausted, and at this time the area of leaves generated in the current year increases rapidly, and the photosynthetic assimilation products produced gradually increase, and the tree begins to gradually shift from the stage dominated by the use of stored nutrients to the stage dominated by the use of assimilated nutrients of the current year. In this stage, the nutrient level of the tree is closely related to the growth rate of walnut leaf area, leaf size and photosynthetic intensity. Therefore, scientific fertilization and improving the nutritional status of the tree are important technical approaches to achieve high yield and high quality of walnuts.