Detailed Explanation of Key Technical Points for Deep Plowing and Soil Improvement in Walnut Orchards

  Deep plowing and soil improvement is one of the main technical measures for improving soil in walnut orchards, and is suitable for areas with poor soil conditions. Through deep plowing, on the one hand it can play a role in storing water and preserving moisture and improving soil structure; on the other hand it can enhance the activity of soil microorganisms, accelerate soil maturation, and increase soil fertility. Deep plowing and soil improvement creates good growing conditions for the root system and improves the absorption capacity of the tree body, thereby promoting the growth and fruiting of walnuts.

Pictured: walnut

  The most suitable time for deep plowing is after fruit harvest and before leaf fall. Because before and after fruit harvest is the peak period of root growth, at this time wounds caused to the root system by deep plowing heal easily, and cutting off part of the root system can stimulate the growth of a certain number of new roots and fibrous roots; combined with fertilization and irrigation, the effect will be even better. Deep plowing can also be carried out in summer in combination with pressing in green manure and straw, in order to increase soil organic matter and improve the soil.

  Deep plowing is divided into expanded-hole deep plowing and whole-orchard deep plowing. Expanded-hole deep plowing is carried out in combination with autumn application of base fertilizer. For young walnut trees, 2~3 years after planting, the planting holes are expanded outward year by year through deep plowing until the entire area between trees has been turned over; generally 3~4 years are needed to complete whole-orchard deep plowing. For mature trees, at the edge of the vertical projection of the canopy, a ring ditch or parallel ditch is dug every year or every other year, with a ditch width of 40~50 cm and a depth of 60~80 cm, with the criterion being not to damage roots 1 cm thick. Topsoil and subsoil are placed separately on the west side of the ditch, straw is placed at the bottom of the ditch, and when the soil is backfilled it is mixed with organic fertilizer; topsoil is placed in the lower layer and subsoil in the upper layer, then fully irrigated.

  For walnut orchards under long-term extensive management, if the soil is severely compacted, the method of using explosives to loosen the soil can be used to achieve deep plowing. This can avoid the drawback of excessive root damage from deep plowing, and can also loosen the soil, promote microbial activity, and preserve water, fertilizer, and heat, while saving time and labor compared with manual deep plowing.

  Soil improvement mainly refers to improvement measures carried out for poor soils such as sandy soil, clay soil, and saline-alkali soil. If a walnut orchard is established on river beach land, then sand removal and soil replacement or soil covering must be carried out. When removing sand and replacing soil, remove sand 1 m wide and 30 cm deep according to the row spacing, replace it with the same volume of loam, and then turn and mix it evenly top to bottom to a depth of 50~60 cm. When covering with soil, spread loam 30~40 cm thick uniformly over the whole orchard, then carry out deep plowing or deep turning so that the sand and soil are mixed. In some pure sandy lands, where clay lies below 30~40 cm, deep plowing should be used to turn the lower clay up to mix with the upper sandy soil. Sandy soil requires large amounts of organic fertilizer and the planting of barren-tolerant green manure in order to improve the physical and chemical properties of the soil. For walnut orchards whose plow layer is clay, it is best to use the method of mixing in sand and replacing soil to increase soil permeability and improve fertilizer supply capacity, while applying more decomposed organic fertilizer to improve soil structure and increase soil organic matter content. For walnut orchards on saline-alkali land, the main approach should be to increase the application of organic fertilizer and appropriately control the amount of chemical fertilizer used, while combining straw return to the field and planting saline-alkali-tolerant green manure and other methods to reduce saline-alkali damage. Increase phosphate fertilizer, apply nitrogen fertilizer in appropriate amounts, and apply little or no potassium fertilizer. In alkaline soil, more physiologically acidic fertilizers should be applied to improve the soil, such as superphosphate, ammonium sulfate, and so on. When conditions permit, irrigation can be used to press down alkali and wash away salt.