Why is it so important to apply "postpartum fertilizer" after fruit harvest?
Applying base fertilizer to fruit trees in autumn increases the tree's stored nutrients, and is the single most important and most critical fertilization for promoting tree vigor and, in the following year, flowering, fruit set, young fruit cell formation, strong new shoot growth, early leaf area formation, shortening the nutrient conversion period, and early entry into flower bud physiological differentiation with sufficient nutrient reserves. Never be careless or negligent about it. Fruit growers vividly call autumn fertilization "postpartum fertilizer," just like a woman who has been pregnant for ten months and has just given birth, physically and mentally exhausted with nutrients depleted, must promptly and substantially replenish nutrients to ensure the health of both mother and child.
After the later stage of fruit enlargement, the tree's nutrient reserves are already depleted by harvest. Especially for late-maturing apples, if sufficient base fertilizer is not applied promptly after harvest, the tree's stored nutrients will be severely deficient. This will not only cause rot disease to spread and become disastrous in winter and spring, but will also seriously affect flowering, fruit set, and young fruit cell formation the following year, resulting in weak flower clusters, low fruit set rate, small young fruit, thin and weak new shoots with small leaves, and a prolonged nutrient conversion period.
Base fertilizer is the most fundamental and most important fertilization in an orchard; it relates to the supply of various nutrients throughout the tree's annual cycle. Autumn base fertilization should be carried out with attention to timing, rationality, and scientific soundness. The fertilization time is generally in September-October. Apples have a proportional requirement for nitrogen, phosphorus, and potassium nutrients, and organic fertilizer should also be added, along with appropriate medium and trace elements; the fertilization method is trenching or hole application; the fertilization location is inside the outer edge of the tree canopy; the fertilization depth is generally 20-40 cm in the concentrated root distribution layer. For root application, dig a shallow trench under the outer canopy projection, generally 150-200 cm long, about 40 cm wide, and 40 cm deep. Autumn fertilization can increase the fruit set rate by 8-10% and increase yield by 10-15% compared with spring or winter application, and its yield-increasing and quality-improving effects are very obvious.
Autumn fertilization has other benefits as well
First, the nutrients consumed by fruit trees from early spring bud break to flowering and fruit set mainly come from the nutrients stored in the tree from the previous year. The period from fruit harvest to leaf fall is the best time for accumulating nutrients, and autumn base fertilization can increase the tree's nutrient reserves.
Second, autumn is the last growth peak of the root system in the year, when its life activities are vigorous and its nutrient absorption capacity is strong, and it also helps delay leaf senescence, enhance the photosynthetic capacity of autumn leaves, and increase the tree's nutrient reserves.
Furthermore, in autumn the soil temperature is relatively high and the soil moisture is relatively good, which is favorable for soil microbial activity. The applied organic fertilizer decomposes quickly and is easily absorbed and utilized by the root system. Some studies have shown that autumn fertilization can increase the fertilizer efficiency of nitrogen, phosphorus, potassium, calcium, and magnesium by 1 time, 5 times, 3 times, 2 times, and 2 times respectively.
Finally, autumn fertilization can improve the root growth environment and enhance the tree's stress resistance. Combining autumn fertilization with deep soil plowing can optimize soil structure, improve soil aeration conditions, facilitate root respiration and growth, and improve the soil's ability to retain water and fertilizer and to resist cold and survive the winter.
Therefore, whether base fertilizer is applied in autumn, winter, or spring, from purchasing fertilizer to applying it, the money and labor spent are the same, but the fertilization results obtained are completely different.
Therefore, many experts and professors call for this: for fruit trees, autumn base fertilization is "gold," winter base fertilization is "silver," and spring base fertilization is "scrap copper and iron." Fruit grower friends should fully understand the important meaning behind this.