Soil management in walnut orchards can adopt the orchard grass-cover technique

  Orchard grass-cover is an advanced, practical and efficient soil management method, especially suitable for walnut orchards with severe soil erosion and poor soil, and it is also one of the important technical measures for producing green fruit and pollution-free fruit. Compared with other soil management methods, orchard grass-cover has better comprehensive economic benefits. Orchard grass-cover can prevent and reduce soil moisture loss, increase soil organic matter content, improve soil fertility, improve soil physical and chemical properties, regulate soil temperature and humidity, and benefit the growth and absorption activity of fruit tree roots. Orchard grass-cover increases the population of natural enemies of pests, thereby reducing pesticide input and pollution caused by pesticides. Orchard grass-cover can enhance the drainage capacity of the soil, facilitate mechanical operations, and prevent environmental pollution caused by wind-blown sand and dust in winter and spring.

  Orchard grass-cover can be whole-orchard or strip planting of sown grass, or natural grass-cover after removing unsuitable species and malignant weeds.

  Sown grass-cover mainly uses the direct seeding method. The width of the grass strips between fruit tree rows should be determined by the spacing between plants and rows and the age of the trees; young orchards can have wider grass strips, while mature orchards can have narrower ones. Suitable grass species for sown grass-cover include: white clover, flat-stemmed milkvetch, Japanese clover, alfalfa medic, crown vetch, Kentucky bluegrass, creeping bentgrass, buffalograss, Chinese leymus, zoysia grass, timothy, melilot, purple alfalfa, bird's-foot trefoil, orchardgrass, ryegrass, etc. Sown grass-cover can use a single grass species or a mixture of two or more grass species. Usually, a mixture of white clover and bluegrass is chosen. White clover belongs to the legume family, has nitrogen-fixing ability, and can enrich the soil; bluegrass is drought-tolerant and highly adaptable, and the mixed planting of the two grasses can give play to their respective advantages, with better results than a single grass species. However, white clover has poor drought tolerance, and in dryland orchards, the seedling death rate of white clover is generally above 30%. Therefore, grass species should be selected according to local conditions based on the soil conditions of the walnut orchard and the age and size of the walnut trees. In irrigated areas, shade- and moisture-tolerant white clover can be selected as the main species, while in dryland areas, more drought-resistant bird's-foot trefoil and flat-stemmed milkvetch can be selected as the main species. For whole-orchard grass-cover, grass species with good shade tolerance should be selected.

  Natural grass-cover is the approach of using natural weeds in the orchard for grass-cover, allowing weeds to sprout and grow during the growing season, and manually removing or controlling weeds that do not meet the conditions for grass-cover, such as lamb's quarters, groundsel, white wormwood, thatch grass and other taller plants.

  Implementing orchard grass-cover is an efficient method of soil management in walnut orchards, but after grass-cover is established, management must be strengthened in order to give play to the comprehensive benefits of orchard grass-cover and achieve the goals of high yield and high quality. Therefore, after the grass species emerge, timely irrigation should be carried out according to soil moisture, nitrogen fertilizer should be applied with the water, and weeds should be removed in time. When there are broken rows and missing plants, timely replanting should be noted. Generally, when the grass grows to more than 30 cm, it should be mowed in time, with 2~4 mowings per growing season. Mowing can control the height of the grass, promote tillering and branching of the grass, increase the coverage rate and increase the grass yield, and the cut grass is used to cover the tree disk. The stubble height of the grass is related to the grass species; generally, gramineous grasses should retain the growing point (below the heart leaf), while leguminous grasses should retain 1~2 nodes of the stem. Mowing of the grass uses a dedicated mower. Grass that grows in autumn is no longer mowed, and the stubble is left to cover in winter.

  It should be noted that grazing must be prohibited in walnut orchards with grass-cover, and after autumn the tree trunks should be whitewashed or wrapped with plastic film to prevent rodent damage, and attention should be paid to fire prevention in winter and spring. As soil fertility improves, the amount of base fertilizer applied can be gradually reduced. Base fertilizer can be applied in the non-grass-cover strips. In walnut orchards with whole-orchard grass-cover, when fertilizing, an iron shovel can be used to turn up the soil with grass, and after applying fertilizer, the soil with grass is put back in place and compacted. Grass-cover orchards should preferably implement water-saving irrigation measures such as drip irrigation and micro-sprinkler irrigation to prevent flood irrigation. When spraying in the orchard, avoid the grass to protect the natural enemies in the grass. Pay attention to cleaning the orchard in time after scraping tree bark and pruning diseased branches and leaves. Under normal circumstances, after 5 years of orchard grass-cover, the grass will gradually age, and it should be turned under and renewed in time, leaving the land fallow for 1~2 years before re-seeding grass. In some areas, the methods of spraying herbicides and mulching with plastic film are also used to renew the grass.