524 



EXPERIMENT STATION RECORD. 



"A fact which makes more remarkable this extraordinary power of the soils to 

 absorb and retain a sufficient quantity of water for the needs of crops for 5 or 6 

 months after the rain ceases is the very low relative humidity of the atmosphere. 

 Records of the relative humidity have been taken from only a few of the places 

 under consideration, and these are given in the following table: 



Mean annual and seasonal relative humidity. 



Locality. 



Tulare, Cal 



Wallawalla, Wash 

 Milea City, Mont. 

 Bismarck, N. Dak 

 Humboldt, Nev. . . 



Annual. 



Per cent. 

 58 

 62 

 65 



72 



May in 

 Septem- 

 ber. 



Per cent. 

 42 

 47 

 52 

 67 

 36 



July and 

 August. 



Per cent. 

 35 

 39 

 46 

 65 

 31 



"The mean relative humidity of New England for July and August, 1897, deter- 

 mined from the reports of 7 Weather Bureau stations, was 85 per cent. At "Walla- 

 walla the mean relative humidity from May to September was only 47 per cent and 

 for July and August 39 per cent. It is hardly conceivable that under these extremely 

 dry conditions the foothills soil could maintain sufficient water from the winter 

 rains to supply the loss due to evaporation from the surface of the soil and to tran- 

 spiration by the plant for months after the rain had ceased to fall. At Tulare the 

 mean relative humidity during the growing season is 42 per cent and 35 per cent 

 during the months of July and August — conditions which practically prevail at 

 Fresno. Nevertheless, at Fresno, with nearly the same rainfall, and where crops 

 must transpire great quantities of moisture iuto the dry atmosphere, the soil main- 

 tains an adequate supply of moisture for the plants, provided the water continues 

 to run in the canals, although these may be as much as a mile apart. . . . 



" At Humboldt, on the Nevada desert, the relative humidity from May to Septem- 

 ber is about 36 per cent and in July and August 31 per cent. The conditions over 

 the Mohave desert are probably uot dissimilar from those at Humboldt and Tulare." 



These peculiar soil conditions suggest the importance of study of "the 

 great power these soils have of retaining moisture and of supplying it 

 rapidly and regularly to the crops as it is needed. If such power can 

 be imparted to other soils of a droughty character, especially to our 

 soils in the East, it will be of immense value to the farmer. 



"The first question to solve is the distribution of the rainfall. It is 

 important to determine the depth to standing water; that is, the aver- 

 age depth of wells. Then it is very important to know whether any 

 portion of the rainfall passes down into this stratum and runs off into 

 the drainage." The use of the electrical method for this purpose is 

 explained. 



It is important to know whether the annual rainfall in these soils 

 descends low enough to form any connection with the underground 

 drainage water, and if it does not, whether the small amounts of rain- 

 fall occurring during the winter months in these regions are "sufficient 

 to maintain crops for 5 or 6 months of dry weather," with "a low rela- 

 tive humidity and often high temperature of the atmosphere, without 

 any additional water supply from any source." 



