the growth of apple is actually divided into two staggered growth forms: vegetative growth mainly consisting of long branches and leaves and reproductive growth mainly consisting of flowering and fruiting.
in fact, the growth of branches and leaves is also to provide sufficient organic nutrition for fruit growth.
before fruit enlargement, nitrogen and phosphorus-based fertilizers were supplied to ensure the normal development of green organs and to form more green photosynthetic tissues. this period is called nitrogen nutrition period.
once in the expansion stage, apples will be transformed from nitrogen nutrition stage to sugar nutrition stage, and carbohydrates produced by photosynthesis of green organs will be transported to fruits for expansion.
therefore, nutritional supplements such as potassium, calcium, magnesium and boron should be paid attention to in this period. while meeting the nutritional needs of photosynthesis in green organs, these photosynthates should be transported to fruits as much as possible.
i. potassium supplement
potassium is not a component of plant organs, but it is an indispensable "role" in physiological activities such as nutrient synthesis, transportation and transformation in plants. applying sufficient potassium fertilizer in this period can promote fruit enlargement and better taste.
ii. phosphorus and nitrogen supplementation
appropriate phosphorus nutrition is not only conducive to flower bud differentiation, but also conducive to the transport and transformation of organic nutrients.
nitrogen supplementation is a point of reconciliation in this period. inadequate nitrogen nutrition can easily lead to premature senescence of fruit trees or even early deciduous fruit. too much nitrogen nutrition can easily lead to vigorous growth of branches and leaves, which is not conducive to the flow of photosynthates to fruits, resulting in small fruits, poor quality and even abscission.
therefore, fertilization in this period should be based on the principles of tree fertilization and soil fertilization.
more fertilizer should be applied to the weak trees with large fruits, a small amount of topdressing should be applied to the vigorous trees with small fruits when the shoots stop growing to promote flower bud differentiation, middle and late topdressing should be added to the "big year" trees, and the "small year" trees should focus on topdressing before and after germination.
especially for fruit trees in the middle and later stages of topdressing, the time should not be too late, the number should not be too much. in order to avoid greedy shoots and excessive growth in late autumn, reduce the level of nutrient accumulation and cold resistance of trees, but also affect the color and quality of fruits. conditions can be matched with appropriate amount of high-quality organic fertilizer to improve soil and promote the absorption of aging roots.
sandy land has poor fertilizer and water conservation capacity, so we should apply less fertilizer diligently, and do not water after topdressing, so as to avoid the loss of water and fertilizer. in saline-alkali land, the available phosphorus content in soil is low. additional phosphorus fertilizer should be added when topdressing.
3. calcium supplementation
calcium is an indispensable nutrient element for the development of fruit epidermis. adequate calcium nutrition can not only reduce the occurrence of bitter pox, but also reduce fruit cracking, promote the brightness of the pericarp, which is essential to improve the quality and storage resistance of fruit.
iv. supplement of magnesium
magnesium supplementation can enhance photosynthesis and chlorophyll content to ensure the demand for fruit expansion. it should be noted that magnesium deficiency symptoms of chlorosis between veins often occur in leaves near large fruit volume during fruit expansion period, which can be prevented by spraying 500-700 times of liquid magnesium sulfate.
v. boron supplementation
boron, as an important nutrient element in this stage, plays an important role in rapidly increasing carbohydrate transport and fruit formation.
if the nutrient is not in place at flowering stage, the high quality liquid boron fertilizer can be sprayed 800-1000 times again.
this topdressing can effectively accelerate the rapid expansion of fruits and increase the cell expansion rate of fruits. it plays an important role in increasing yield, overcoming the "big and small years" of trees and promoting flower bud differentiation.