What are the main fertilization methods for walnut trees? A detailed explanation of key fertilization points

  The walnut fertilization methods currently used in China are mainly two types: soil fertilization and foliar spraying.

  Soil fertilization can be carried out in combination with soil ploughing. In order to facilitate root absorption and utilization and maximize fertilizer efficiency, when applying soil fertilizer, the fertilizer must be placed in the concentrated distribution layer of the root system. The specific methods are as follows; the most suitable fertilization method can be selected according to actual conditions.

  (1) Ring trench fertilization: Dig a ring-shaped trench along the outer edge of the tree canopy's ground projection, with a trench width of 30-40 cm, a base fertilizer trench depth of 30-50 cm, and a topdressing trench depth of 15-20 cm. Mix the fertilizer evenly with the topsoil and apply it into the trench, then cover with subsoil. The ring trench should be moved outward year by year. This method is simple to operate and economical in fertilizer use, but the fertilization area is relatively small, so it is often used for young walnut trees under 5 years old.

  (2) Radial trench fertilization: This is the main fertilization method used in walnut orchards over 5 years old. Generally, based on the tree canopy's ground projection, with 2/3 extending inward and 1/3 extending outward, dig 4-8 radial trenches, with a trench length of 1-2 m, a trench width of about 30 cm, and a trench depth of 25-30 cm. Apply fertilizer in the trenches, cover with soil, and irrigate. The positions of the fertilization trenches should be staggered each year. When digging trenches, try to avoid damaging large roots with a diameter of more than 1 cm.

  (3) Strip trench fertilization: Suitable for young trees, mature trees, and densely planted orchards. It involves digging trenches between walnut trees or between rows, on one or both sides of the canopy projection, with a length about 2/3 of the crown diameter or equal to the crown diameter. The trench width is 40-50 cm, the base fertilizer trench depth is 40-60 cm, and the topdressing trench depth is 15-20 cm. Rotate the trench digging between rows and between trees each year for fertilization, which can be combined with deep soil ploughing. This method causes relatively less root damage, but the fertilization position is limited. It can be used alternately with radial trench fertilization to expand the fertilization area and promote root absorption.

  (4) Hole fertilization: Suitable for walnut orchards with larger canopies, wider root distribution, and intercropping between rows, and is mostly used for topdressing. With the trunk as the center, at positions 1-1.5 m away from the trunk, dig several fertilization holes with a diameter of 30-40 cm and a depth of about 25 cm, apply fertilizer into them, seal with soil, and then irrigate. This method saves fertilizer and is simple to carry out.

  (5) Whole-orchard broadcasting: In walnut orchards at full fruiting stage, the tree roots have spread throughout the entire orchard. When applying base fertilizer, organic fertilizer can be evenly scattered on the ground and then ploughed into the soil, generally to a depth of about 20 cm. This method is simple and easy to carry out; the disadvantage is that the fertilization position is relatively shallow, which can easily cause roots to grow upward.

  In addition, topdressing can also use the fertigation method, dissolving soluble fertilizer in water and applying it with water through a drip irrigation or seepage irrigation system. This method supplies fertilizer promptly, distributes it evenly, does not damage roots, does not destroy soil structure, and can also save chemical fertilizer. This method is also called "integrated water and fertilizer management."

  (6) Foliar spraying: Also called foliar topdressing, it involves directly spraying a fertilizer solution of a certain concentration onto the leaf surface. This method uses less fertilizer, has a quick fertilizer effect and high utilization rate, can promptly meet the walnut tree's nutrient needs, and at the same time can avoid the disadvantage that some elements in soil fertilization will be fixed. Foliar spraying can be carried out separately at the flowering stage, the rapid shoot growth stage, the flower bud differentiation stage, and after harvest. Choose clear and windless weather, and carry out foliar spraying before 10 a.m. or after 4 p.m. When the temperature is too high, the solution will concentrate and cause leaf scorch. Generally, the underside of leaves has a stronger ability to absorb fertilizer, so when carrying out foliar spraying, focus on spraying the underside of the leaves. The types and concentrations of foliar spraying are: urea 0.3%-0.4%, superphosphate 0.5%-1%, potassium sulfate 0.2%-0.3% (or 1% wood ash extract), boric acid 0.1%-0.2%, ammonium molybdate 0.5%-1%, copper sulfate 0.3%-0.4%. In Shexian, Hebei, spraying 0.3% boron plus 0.3% urea at the walnut flowering stage can increase the fruit-setting rate by 9%-17%. The general principle of foliar spraying is low concentration in the early growth stage and high concentration in the later stage. In actual use, a small-scale test should be conducted first to avoid phytotoxicity caused by excessively high concentration. It should be noted that foliar topdressing is only a supplementary fertilization measure and cannot replace soil fertilization. If the two fertilization methods are used in combination and complement each other, they can maximize the effect of fertilization.