What ecological conditions are needed for the growth and development of walnut trees?

  Different walnut species and cultivars vary greatly in their ability to adapt to rainfall.

  In the distribution area of Yangbi walnut, the annual rainfall is 800-1,200 mm, while introducing early-bearing walnuts to areas with rainfall above 6,00 mm makes them prone to disease. Walnut tolerates dry air, but is relatively sensitive to soil moisture conditions; soil that is too dry or too wet is unfavorable for the growth and fruiting of walnut.

Pictured: walnut

  For example, in major walnut-producing areas such as Kuqa and Hotan in Xinjiang, the annual rainfall is only 37.5-82.8 mm, and the average relative humidity from April to September is only 31%-40%. Although it is very dry, the walnuts grow well because of good irrigation conditions. A long period of clear, dry climate, ample sunlight and a large day-night temperature difference help promote flowering and fruiting and improve fruit quality. The early fruiting and high yield of Xinjiang walnut were formed precisely under such conditions over the long term. Soil drought hinders root absorption, affects metabolic functions, and causes flower and fruit drop and even leaf wilting. If young walnut trees experience drought in the early part of the growing season and abundant rain later, the branches are prone to excessive vegetative growth, causing winter dieback of shoots. Too much soil moisture and poor aeration obstruct root respiration and, in severe cases, can suffocate the roots and affect tree growth and development. Therefore, walnut orchards on hillsides need soil and water conservation engineering measures, while on flat land the drainage problem must be solved. The groundwater level in a walnut orchard should be below 2 m from the surface. Research has shown that the height of the groundwater level affects the depth of walnut root distribution.

  Research by Hebei Agricultural University has shown that climatic conditions have an important influence on the growth, development, flowering and fruiting of walnut. In particular, the average temperature, sunshine and rainfall in July and October of the previous year, as well as the climatic conditions in March-April of the current year, play an important role in flower bud differentiation, flowering, pollination, fruit set and fruit development of walnut, and have a clear impact on yield. When there is more rain in July of the previous year, sufficient sunshine, and a higher average temperature in October, the walnut yield increase the following year is obvious, showing a positive correlation that can be used to predict yield.