It is almost universal history that in farming a newly developed region no attention whatever is paid to maintaining the fertility of the soil. This is natural for two very obvious reasons. In the first place the pioneer has other and more pressing problems in the "subduing" of the new land, and in the second place such virgin soils are generally blessed with a great abundance of native fertility. New lands in an arid or semiarid region are usually especially fertile because they represent a long-time accumulation of fertility which is not possible under humid conditions. Since in a humid region the tendency for evaporation is not sufficient to remove all of the water that goes into the soil, there is always a certain excess that seeps downward to the water-table and is later removed by springs and rivers. This seep water constantly carries away a certain amount of the soluble salts that serve as food for plants. In an arid climate, on the other hand, the evaporating tendency is more than sufficient to remove all the water that goes into the soil so that the ultimate movement of the soil moisture is upward. This soil moisture leaves all its soluble material at the surface as it evaporates, and thus there is an accumulation of mineral plant-food. (This accumulation of soluble material at the surface may become excessive, in which case we have "alkali" -but that is another problem.) On the other hand, the organic matter or "humus" of the soil contains most of the nitrogen (one of the most important plant-foods), and this does not move with the water but rather is lost by slow oxidation or burning up, so that this element of plant-food is lost more rapidly from the well-aerated soils of the arid region than from soils in a humid climate.
Pittman, D. W., "Bulletin No. 188 - Maintaining the Productivity of Irrigated Land" (1924). UAES Bulletins. Paper 154.