Characteristics of Fertilizer requirement for growth and Development of Walnut trees

   walnut likes fertilizer, but the fertilizer requirements are different in different age periods and different phenological periods.

The fertilizer requirement of    walnut was different at different ages. The ontogeny of walnut trees can be divided into four stages: young stage, early fruiting stage, full fruiting stage and aging stage. In the young stage, vegetative growth is dominant, and the trunk, branches and roots grow rapidly and accumulate nutrients for flowering and fruiting. In this period, there is a great demand for nitrogen fertilizer, so we must ensure an adequate supply of nutrients and pay attention to the application of phosphorus and potassium fertilizer. At the initial stage, the vegetative growth began to slow down, the reproductive growth increased rapidly, the tree continued to expand its roots and crown, a large number of fruiting branches were formed, the yield increased year by year, and the demand for various nutrients increased, especially the demand for phosphorus and potassium fertilizer. In the full fruit stage, the vegetative growth and reproductive growth reached a relative balance, the crown and root reached the maximum range, the branches and roots began to renew, and the tree needed a lot of nutrition, in addition to ensuring the supply of nitrogen, phosphorus and potassium, the application of organic fertilizer is one of the important measures to ensure high and stable yield. In the aging period, the yield began to decline, the growth of new shoots was very small, and a large number of internal fruiting branches weakened until death. In this period, it can be combined with regeneration, rejuvenation and pruning, increase the application rate of nitrogen fertilizer, promote vegetative growth and restore tree potential.

The fertilizing period of    walnut is related to the phenological phase. In the spring sprouting period, the new shoots have more growth points and growth, and have a greater demand for nitrogen; the reproductive growth in the flowering stage has a greater demand for phosphorus; in the fruit-setting period, there is a large amount of nutrient transport and more potassium. The three critical periods of nutrient requirement of walnut were budding stage, flowering stage and hard kernel stage, respectively. In the whole annual cycle, the nutrient demand is the highest in the flowering and fruit setting stage. After the leaf bud germination of walnut in spring, the physiological activity is increasingly exuberant, the growth and development is accelerated rapidly, the metabolism is enhanced, and a large number of nutrients and energy substances are needed in order to make the physiological activities such as branch and leaf development, flowering and fruiting proceed smoothly. After flowering, walnut should supplement a large amount of nutrients consumed at flowering stage and meet the nutritional needs of young fruit growth, so as to provide a guarantee for reducing physiological fruit drop and increasing fruit setting rate. During the hard core stage (June), walnut endocarp hardens, nucleolus develops, and flower buds begin to differentiate, both of which require a lot of phosphorus and potassium. If the fertilization is timely, the amount of fertilizer is sufficient, and the elements are coordinated, it is not only the guarantee of high yield in that year, but also the basis of high yield in the next year, which is very important. In addition, there is still a period of growth and development from the harvest of walnuts to the eyes of fallen leaves. During this period, not only the flower buds should be further developed and mature, but also the annual techniques should be mature, and the trees should also store a lot of organic matter in order to survive the winter safely. Therefore, the base fertilizer based on organic fertilizer should be applied as soon as possible in autumn, which is the basis and guarantee for a bumper harvest in the coming year.

   generally speaking, walnut needs more fertilizer, especially more nitrogen than other fruit trees. The combined application of nitrogen, phosphorus and potassium has a great effect on the yield of walnut. At the same time, it is emphasized that potassium fertilizer should be applied during the hard core period to promote walnut to survive the winter safely. If walnut trees are lack of trace elements or insufficient supply, physiological obstacles will occur and element deficiency will occur, which hinders normal growth and affects yield and quality. Therefore, the principles of "large amount of fertilizer application, comprehensive elements, coordinated proportion, timely fertilization and appropriate methods" should be grasped in the fertilization of walnut.