the color remains green, because sufficient time has not been allowed for the biological process which causes the color changes to take place. If the leaves remain longer in the hot air current, they may also lose their fermenting power. In order to facilitate the transformation of the matter of the leaves a slow curing is necessary. If, however, the circulation of air is too limited, reduction takes place and the leaves turn black, losing their resistance and elasticity. In a general way ventilation should be slow, with a constant circulation of air around all of the leaves, until the parenchyma changes color. Rapid ventilation should be avoided during the early stages of curing, except for short periods after very damp spells, when it may be resorted to in order to drive out the excess of moisture. High temperature and excessive humidity must be avoided. REPORT OF IRRIGATION AND DRAINAGE INVESTIGATIONS, 1904. By ELWOOD MEAD, Chief of Irrigation and Drainage Investigations. IRRIGATION. IMPROVEMENTS IN METHODS OF IRRIGATION. Measurements of the water used in irrigation have now been carried on for seven years. They show the great difference which exists between good and bad practice, and the benefits which improved methods of applying water will bring. Enormous quantities of water are used under some canals, while equally good results under others having the same conditions are secured with very much less water. The canal of the Turlock irrigation district of California diverted enough water in 1904 to cover the 19,000 acres irrigated to a depth of 8.34 feet, and enough of this water was actually delivered to the land to cover it to a depth of 6.84 feet. The Modesto Canal diverted water enough to cover the land irrigated to a depth of 13.18 feet, and of this enough reached the land to cover it to a depth of 11.13 feet. In the same State and in a section having a longer season and greater evaporation, the water diverted by the Gage Canal for a number of years would cover the land irrigated each year to a depth of 2 feet, or less than one-third the water used under the Turlock Canal and less than one-fifth that used under the Modesto Canal. Measurements of the water used in irrigation along the Raft River in southern Idaho show that enough was used in 1904 to cover the land to a depth of 6 feet. There is great room here for extension of the area by economical use. Measurements of the quantity of water used under the Sunnyside Canal in Yakima Valley, Washington, carried on for several years, show that the land under that canal received water to an average depth of more than 10 feet. Improvements in practice, suggested by reports from this Office and put into effect by the management of the canal, reduced the amount used in 1904 to a depth of 6 feet, a saving of about 44 per cent in the consumption of water, making possible a like increase in the acreage irrigated. That there is room for further improvement in this section is shown by the fact that there are everywhere evidences of overirrigation, in many places the lands being already swamped and in need of drainage. The measurement of water used in 1901 in the Pecos Valley, New Mexico, under the canals of the Pecos Irrigation and Improvement Company, showed that the quantity used by the individual irrigator varied from enough water to cover the land irrigated to a depth of 1.18 feet to enough to cover it to a depth of 14.43 feet, with an average for the system of 3.33 feet. During 1904 the average depth of water used by irrigators in this valley under the Hagerman Canal, as reported by J. J. Hagerman, did not exceed a depth of 2 feet over the land irrigated. In the beginning the studies of the duty of water were directed to determining the amount used in ordinary practice, and instructions were given to irrigators whose water was being measured to use it exactly as though such measurements were not being made. In 1901 these measurements were supplemented by experiments to determine the exact needs of crops. These experiments included the application of different quantities of water to crops to determine the amount which gave the best results, the distribution of water over fields by different methods to determine how losses by seepage and evaporation could be lessened, and variations in both the amount and time of irrigation to determine its influence on the yield and quality of grain, fruits, and vegetables. Through these experiments, it is believed that improvements in methods of application will be made which will result both in a marked increase in the acreage irrigated with a given volume of water and also in increased yields. In many places increase in acreage irrigated must come from more economical use of water. A higher duty of water will make possible the extension of many canals and the irrigation of unused areas under others. The chief losses of water by evaporation come in spreading water over fields. During 1904 experiments were made in California to determine how best to check this great loss. Plates XXI and XXII show methods of placing and weighing tanks used in measuring evaporation losses from the soil. In these experiments water was applied to similar plats by three methods-flooding the surface, in furrows 3 inches in depth, and in furrows 12 inches in depth. Taking the quantity of water evaporated under surface flooding as a basis, applying water in shallow furrows made a saving of 13 per cent, while applying it in deep furrows brought about a saving of 25 per cent. Our experiments, while they show excessive use in many places, show that there is a point beyond which economy in water can not be pushed with profit, because of the reduction in yields which follows. Experiments to determine this were made in several parts of the arid region. The complete tabulation of the results of these measurements has not been made at the time of preparing this report. |