In the Chihuahuan Desert of New Mexico, Trans Pecos Texas and Northern Mexico, we have many mountain ranges that have an ecotone at the base which I call the Desert Edge Woodland. It's very arid, dominated by Quercus species and averages between 12 and 15 inches of annual precipitation, rarely higher. 50% of precipitation falls during the summer monsoon season which is not much when you consider that the daily evaporation rate can exceed 1/2". Despite the aridity the oaks in this ecotone can still reach 40 feet tall or larger and you might assume that when grown for landscaping that these same species could tolerate the same 12 to 15 inches of annual moisture, however they cannot. Under cultivation the Chihuahuan Desert Native Oak will most likely need about 20 to 30 inches of annual moisture supplemented if planted in Albuquerque, Tucson, El Paso or Las Cruces. Nothing close to the 12 to 15 inches of its native counterparts. The reason for the lack of the same hardiness and low water tolerance of the cultivated plant versus the wild plant is that the cultivated plant lacks the full ecology of the terrestrial biosphere including a pipeline of Supramolecular Humic Acids and a Mycorrhizal relationship.
I was recently asked to provide a simplified explanation on the importance of Cation Exchange Capacity (CEC) values. My Response: CEC is the ability of a soil to hold onto plant nutrients. The finer the particle size the higher CEC value, generally speaking. For example sand particles are course and visible to the naked eye, where as clay particles are fine and are not visible to the naked eye. So clay will have a higher CEC value than sand. It is obvious to most of us that sand cannot hold onto water or nutrients as well as a soil with a finer texture. Therefore, soils rich in Clay and Loam size particles are universally recognized as being better for farming - CEC explains this. The numerical value for CEC represents how much nutrition can be held by a given amount of soil. For example one pound of a clay loam soil with a CEC value of 20 will hold 4 times as many nutrients as a sandy soil with a CEC value of 5. 20/4 = 5 . It's all about math, for example Nitrogen in