When Is the Best Time to Fertilize Apple Trees in Autumn? Per-Mu Application Rates and Fertilization Methods

Apple, also known as the peace fruit, wisdom fruit, etc., is a common deciduous tree fruit in China. Because of its high nutritional value and promising cultivation prospects, it is widely planted. But to achieve high apple yields, you must master water and fertilizer management well. So when is the best time to fertilize apple trees in autumn? How much fertilizer per mu? How to apply it?

Fertilization Time

Autumn basal fertilizer is generally best applied from mid-September to late October, and the earlier the better.

How Much Fertilizer per Mu?

Basal fertilizer should be mainly organic fertilizer, with a reasonable combination of chemical fertilizers. The application rate should be determined by soil conditions, tree species and tree age, and should account for 60% of the annual total. Generally, orchards on mountain and sloping land have thin soil, so the application rate should be larger; orchards on flat land with fertile soil can be given less. For mature trees, orchards with a per-mu yield of more than 2,000 kg require 1 kg of organic fertilizer per kg of fruit; orchards with a per-mu yield of 2,500-3,500 kg require 1.5 kg of organic fertilizer per kg of fruit, plus an appropriate amount of quick-acting nitrogen and phosphorus fertilizers. Young trees should be given 1,000-1,500 kg of decomposed organic fertilizer per mu and 15-50 kg of urea; for mature orchards, the application rate is calculated on the basis that 100 kg of apples require 1.0-1.1 kg of pure nitrogen, 0.6-0.8 kg of phosphorus and 0.8-1.0 kg of potassium.

Fertilization Principles:

Autumn basal fertilization should adhere to the principles of being decomposed, early, sufficient, complete and even. First compost and decompose the organic fertilizer, then apply it as early as possible. The amount applied must be sufficient, accounting for 60% of the annual fertilization rate; the fertilizer composition must be complete, combining organic, inorganic, major and trace elements; the fertilization site should be appropriate, in the concentrated root distribution zone, in the middle and lower layers; mixing should be even, with fertilizer thoroughly mixed with fertilizer and with soil; basal fertilizer should be mainly decomposed organic fertilizer, with an appropriate application of some quick-acting nitrogen, phosphorus and potassium fertilizers, trace element fertilizers and biological bacterial fertilizer.

The Role of Applying Organic Fertilizer in Autumn

Organic fertilizer refers to barnyard manure, green manure, cow dung, sheep dung, chicken manure, cake fertilizer, biogas fertilizer, etc. Applying organic fertilizer in autumn can improve soil structure, meet the fruit tree's demand for various mineral nutrients, help form soil aggregates, and enhance the soil's ability to retain fertilizer and water. Applying organic fertilizer in autumn has many benefits.

1. In autumn, the soil temperature is suitable and the soil moisture is good, which favors fertilizer decomposition, makes it easy for roots to absorb, and significantly improves fertilizer efficiency.

2. It can supply various nutrients over a longer period, helping coordinate vegetative growth and reproductive growth, enhancing leaf function and increasing nutrient accumulation, promoting plump and well-developed branches and buds, and improving tree resistance. In the following spring, buds sprout early, flowering is uniform, fruit set is greater, fruit is larger, spring shoots grow rapidly and can stop growing in time, making it easy to form flower buds.

3. The fertilizer effect is steady and slow, and can effectively regulate “alternate bearing”.

4. Autumn fertilization coincides with the third peak growth period of the root system; damaged roots heal easily and a large number of new roots can be promoted, enhancing absorption capacity.

Fertilization Methods

Because organic fertilizer has poor mobility, it must be applied to the concentrated distribution layer of absorbing roots, that is, 30-40 cm beyond the outer edge of the branch spread.

1. Young trees. Expand the planting hole, expand the ditch, apply in a ring-shaped ditch or a strip-shaped ditch. The ditch should be 50 cm wide and 25-30 cm deep.

2. Fruiting trees. Apply in radial ditches or strip-shaped ditches, 30-40 cm deep and wide, or broadcast over the whole orchard. Alternate the above methods every other year.

3. The method combining basal fertilizer with “ditch grass” (storing fertilizer and water in pits). In areas with poor irrigation conditions, dig pits 100 cm square between tree rows or between plants, mix weeds or straw with organic fertilizer and fill them into the pits, and apply an appropriate amount of quick-acting nitrogen, phosphorus and potassium fertilizer or special fertilizer for fruit trees. Tie a grass bundle in the middle of the pit, cover it with a plastic film with a hole left in the middle so the grass bundle protrudes, and pour in an appropriate amount of water. Rainwater or irrigation water can seep in through the hole.

Irrigation after Fertilization

Fruit trees can only absorb nutrient elements in a water-dissolved state. In other words, water and fertilizer go together, and fertilization must be accompanied by irrigation.