ABSTRACT
Walnut (genus Juglans) is known for the nuts and timber it produces. There are many species but it is the Persian walnut (Juglans regia), which is best known and grown most extensively in the world as a food crop. It is also commonly known as the "English" walnut but the name Persian is preferred because it indicates the area in which the species probably originated. Walnuts are sensitive to both low and high temperatures. High summer temperatures can result in sunburning of the hull and dark shriveled kernels. Some damage to exposed nuts occurs at 38°C or higher, particularly when the trees are under moisture stress. Walnuts do best on soils where roots can develop uniformly to a depth of 3 to 4 m or more. This requires soil of medium texture free of hardpan or layers of high clay content. Soils of this type are typically associated with alluvial fans of rivers and streams.
