Rainfall Insufficient Or Unevenly Distributed

With these figures on the actual amount of water that a soil may lose in producing certain crops, and with this explanation of where so much of it goes, the farmer may now get from the nearest Weather Bureau a statement of the average amount of water that falls upon his soil each year or he may consult the general rainfall map on another page. Then compare the two sets of figures. At first sight, it may look as though there ought to be no difficulty in watering the crop; the rainfall may be thirty inches and the crop may use but thirteen. But how much of this rainfall comes during the months when the crop is growing ? How much of the rainfall previous to the planting of the crop can be saved in the soil ? These two questions must be answered. The weather man will answer the first; only the farmer can answer the second, for it depends entirely upon the kind of soil he cultivates and upon the way he handles it. A comparison between the average rainfall during the growing season, say from April 1st to September 15th, and the amount of water needed by the crop, may reveal an interesting situation.

It may show, for instance, that the rainfall in those months is equal to or greater than the water used in producing the crop. This would be all right were it not for two facts; quite frequently there are years that fall much below the average in summer rainfall, perhaps considerably below the amount needed by the crop; it is the average of wet years and dry years that gives the "normal" rainfall. Then, again, not all the rain that falls becomes available for plant growth. Some of it runs off as surface water and fills the creek; some of it passes down through the soil; some of it evaporates. Very often not half of the summer rainfall can be utilised by crops. The comparison of figures may show that the total amount of water that falls during the growing season is only about one-third as much as the crop needs.

In nearly all sections of the country the situation is that not enough rain falls during the growing season to water the crops after that lost by surface drainage, evaporation and seepage is deducted. The total rainfall may be adequate, but it is unevenly distributed. The problem, then, is to store the abundant rains of winter and early spring against the dryness of summer; this is one of the most important problems in farming. The water may be stored in reservoirs and used for irrigation or it may be stored in the soil itself; the former is a Western, the latter an Eastern method. Soil storage is more common and requires more skill. The man who has learned to store water in the soil effectively ha? mastered one of the most important problems in crop husbandry.