Key Points for Choosing a Walnut Orchard Site: How to Select a Good Plot for Orchard Establishment
The selection of a walnut orchard site is directly related to the success or failure of pollution-free walnut production and the level of its economic benefits. To achieve the goals of early fruiting, high quality, high yield, high efficiency and pollution-free production as much as possible, a site should be chosen that is flat, has deep soil layers, fertile soil, is sheltered from the wind and facing the sun, and has convenient transportation; at the same time, the site is required to have a good ecological environment with fresh air, pure water and no pollution, and to be far from mines, industrial enterprises and main traffic lines that easily produce pollutants. Avoid planting walnuts on soil where willow and poplar trees have grown, to prevent the occurrence of root rot; avoid continuous walnut cropping for many years, as continuous cropping will greatly increase the density of root-knot nematodes and other pests, affecting the growth and development of walnuts; abandoned land, due to decreased soil fertility and reduced productive performance, must never be chosen as a replanted or abandoned plot.
1. Climatic requirements for walnut orchard establishment sites. From the perspective of geographical distribution, the natural producing areas of walnuts are mostly in warmer zones, with 30°~40° north latitude being the suitable cultivation region for walnuts. In terms of vertical distribution, walnuts grow and bear fruit well in areas at an altitude of 700~1,300 m. Areas with a frost-free period of more than 180 days and an average annual temperature of 8~16°C are all suitable for planting. Walnut trees can withstand low temperatures of -20°C during dormancy, and some varieties can withstand cold down to -30°C. After bud break in spring, cold resistance decreases; if the temperature drops to -4~-2°C, new shoots may be frozen, and if the temperature drops to -2~-1°C during the flowering and young fruit stages, they will be frozen and yields reduced, but this will not cause major damage to mature trees.
Walnut trees are not strict about atmospheric humidity and can still grow and bear fruit normally in a dry climate. Walnut growth and development, however, is more sensitive to soil moisture, and both excessive drought and excessive moisture are unfavorable to walnut growth and fruiting. When water is insufficient at the seedling stage, growth stops. During the fruiting stage under excessively dry conditions, tree vigor is weak, leaves are small, and fruits are small; in this case, watering is necessary. Long periods of clear and dry weather can promote flowering and fruiting. When walnuts are in poorly drained conditions with long-term water accumulation, especially when polluted, oxygen deficiency occurs, causing root rot and even death of the entire tree.
Walnuts have strong adaptability to soil. Whether on hills, mountains or plains, as long as the soil layer is relatively thick and drainage is good, they can grow. In river valley areas with loose soil and good drainage, they grow even better. Under soil conditions with a groundwater level below 1.5 m and a pH of 7.0~8.2, in neutral to slightly alkaline soil, walnut trees grow well.
2. Influence of topography. The general requirements for selecting a walnut orchard site in terms of topography are shelter from wind, facing the sun, air circulation and abundant sunshine. China's mountainous area accounts for more than 2/3 of the country's land area, and walnuts are mostly cultivated on hillside land. Mountains have the characteristics of air circulation, sufficient sunshine and good drainage, but mountainous terrain is complex, the climate is changeable, soil layers are relatively thin, fertilizer and water conditions are relatively poor, and transportation is inconvenient, which brings certain difficulties to walnut production and management. Therefore, when planting walnuts in mountainous areas, special attention should be paid to conditions such as altitude, slope gradient, slope aspect, slope shape and soil layer thickness, as well as the adaptability of walnuts to temperature, light, moisture and other conditions. According to differences in mountain topography, absolute height and relative height, mountains can be divided into hilly zones, piedmont zones, low mountain belts, middle mountain belts and high mountain belts. The slope for establishing an orchard in mountainous areas should be below 20°; if the terrain is not very undulating and the slope surface is relatively regular, especially in the mountainous areas of southwest China, places with a slope >25° can also be appropriately used.
Under specific site conditions, the position and orientation of the terrain can affect light, temperature, soil and moisture conditions, and these change over time. A walnut orchard is best established on flat land or gentle slopes, with an open, sunny slope aspect being preferable. From the existing distribution of walnuts, places with sufficient water sources along streams and on both banks of riverbeds are the best.
3. Influence of slope aspect. For the choice of slope aspect, theory holds that sunny slopes and semi-sunny slopes are best, but under conditions of sufficient light and no irrigation, walnut trees planted on semi-shady and shady slopes are superior to those on sunny and semi-sunny slopes. When planting walnut trees in mountainous and hilly areas, due to the large temperature difference and generally good light conditions, the production and accumulation of photosynthetic products is favored, and high-quality fruit can be produced. However, some unfavorable ecological factors may also arise and affect walnut development.
The degree of slope in hilly and mountainous areas has a relatively large impact on soil fertility and moisture conditions. The greater the slope, the more severe the rainwater erosion, the more serious the nutrient leaching, the more barren the soil, and the less moisture there is, making it more arid. Therefore, areas with steep slopes must have soil and water conservation projects planned. After comprehensively considering various ecological factors and preliminarily determining the orchard site, overall planning and design of the walnut orchard should be carried out, including orchard site survey, main roads, irrigation and drainage systems, establishment of shelterbelts, division of plots and variety combinations, etc.
4. Influence of wind-blown sand and saline-alkali conditions. Because sandy wasteland has strong winds, high sand mobility and poor soil water storage capacity, when planting walnuts on sandy wasteland, shelterbelts should be established as early as possible before orchard establishment, to achieve the goals of windbreak and sand fixation and improving the climate environment of the walnut orchard. On mildly saline-alkali land, through reasonable planning, soil improvement, installation of irrigation and drainage systems and selection of suitable varieties, walnut production can be carried out.