A Detailed Explanation of the Fertilizer Requirements for the Growth and Development of Walnut Trees

  Walnut trees like fertilizer, but the amount of fertilizer needed varies at different ages and different phenological periods.

  The fertilizer requirements of walnut differ at different ages. The individual development of a walnut tree can be divided into four stages, namely the young age period, the early fruiting period, the full fruiting period and the aging period. In the young age period, vegetative growth dominates, and the trunk, branches and root system grow rapidly in length and thickness, accumulating nutrients for the transition to flowering and fruiting. In this period, the demand for nitrogen fertilizer is large, so a sufficient nutrient supply must be ensured, while attention should also be paid to the application of phosphorus and potassium fertilizers. In the early fruiting period, vegetative growth begins to slow down, reproductive growth strengthens rapidly, the tree continues to expand its roots and crown, fruiting branches form in large numbers, yield increases year by year, and the demand for various nutrients increases, especially the demand for phosphorus and potassium fertilizers. By the full fruiting period, vegetative growth and reproductive growth reach a relative balance, the crown and root system reach their maximum extent, branches and roots begin to renew, and the tree needs large amounts of nutrients. In addition to ensuring the supply of nitrogen, phosphorus and potassium, applying more organic fertilizer is one of the important measures to ensure high and stable yields. In the aging period, yield begins to decline, new shoot growth is very small, and internal fruiting branch groups weaken in large numbers until they die. In this period, in combination with renewal and rejuvenation pruning, the application rate of nitrogen fertilizer can be increased to promote vegetative growth and restore tree vigor.

  The fertilizer requirement period of walnut is related to the phenological period. In the spring germination period, there are more new shoot growing points and the growth amount is large, so the demand for nitrogen is relatively large; during the flowering period, reproductive growth has a relatively large demand for phosphorus; during the fruit-setting period, the nutrient transport volume is large, so more potassium is needed. The 3 key periods of nutrient demand for walnut are respectively the germination period, the flower-falling period and the hard-shell period. In the entire annual cycle, the nutrient demand is greatest during the flowering and fruit-setting period. After the leaf buds of walnut germinate in spring, physiological activity becomes increasingly vigorous, growth and development accelerate rapidly, and metabolism strengthens, requiring large amounts of nutrients and energy substances so that physiological activities such as sprouting branches and unfolding leaves, flowering and fruiting can proceed smoothly. After flowering, walnut needs to supplement the large amount of nutrients consumed during the flowering period while also meeting the nutritional needs of young fruit growth, providing a guarantee for reducing physiological fruit drop and increasing the fruit-setting rate. In the hard-shell period (June), the endocarp of walnut hardens, the kernel develops, and at the same time flower buds begin to differentiate; both require large amounts of phosphorus and potassium. If fertilizer is applied in time, the amount is sufficient, and the elements are balanced, then it is both a guarantee of a good yield in the current year and the foundation for a good yield in the following year, which is very important. In addition, from after harvest to before leaf fall and dormancy, walnut still has a period of growth and development. In this period, not only must the flower buds further develop and mature, but the one-year-old branches must also develop and mature, and in order to overwinter safely, the tree must also store large amounts of organic substances in its body. Therefore, in autumn, base fertilizer mainly consisting of organic fertilizer should be applied as early as possible. This is the foundation and guarantee for obtaining a bumper harvest the following year.

  Overall, walnut has a large fertilizer requirement, especially its nitrogen requirement is greater than that of other fruit trees. The combined application of the three fertilizers nitrogen, phosphorus and potassium has a great influence on walnut yield. At the same time, potassium fertilizer application during the hard-shell period is emphasized in order to promote the safe overwintering of walnut. If a walnut tree lacks trace elements or their supply is insufficient, physiological disorders will occur and deficiency symptoms will appear, hindering normal growth and affecting yield and quality. Therefore, for walnut fertilization, the principles of "large fertilizer application amount, comprehensive elements, coordinated proportions, timely fertilization, and appropriate methods" should be mastered.