WATER SOILS. 535 



" If we express the changes in the water content in pounds which the percentages 

 indicate then the upper- 3 ft. of the not subsoiled area gained during the 6 days 

 12! i. 69 lbs., while the lower 2 ft. lost 53.52 lhs. . . . On the other hand, the suhsoiled 

 area in its upper 3 ft. lost 11.14 lbs., while the lower 2 ft. gained 39.38 lbs., making 

 the absolute gain to the area only 28.24 lbs." 



In the fourth experiment 2 plats which had been subsoiled in the lat- 

 ter part of June "were allowed to stand until September 9 unprotected 

 and undisturbed in any way, except that weeds were kept from growing 

 upon them by shaving them off with a hoe. Samples of soil were taken 

 [to the depth of 5 ft. J at 4 places on each of the subsoiled areas and at 

 5 places on the intervening not subsoiled area. . . . 



"On the subsoiled ground there was found more water in the second, 

 third, and fourth feet than was found in the soil not so treated, but the 

 surface foot was markedly drier." 



A general explanation of the effects of subsoiling on soil moisture is 

 given. 



An electrical method of determining the moisture content, 

 temperature, and soluble salt content of soils, M. Whitney, F. 

 D. Gardner, L. J. Briogs, and T. II. Means ( U. S. I>ept. Ayr., Divi- 

 sion of Soils Buls. (J, pp. 26, figs. 6 ; 7, pp. 15, fig. 1 ; 8, pp. 30, Jigs. 0). — 

 The method proposed for determining moisture is based upon the fact 

 that the electrical conductivity of a soil depends principally upon three 

 factors. 



" [These factors] which as a rule are constantly changing, are the temperature 

 the water, and the soluble salt; in other words, the amount and concentration of 

 the salt solution and the temperature Therefore, to determine the temperature of 

 the soil, the water content, or the amount of salt dissolved in the water, it is neces- 

 sary to know two of these three values at the time of observation in order to establish 

 the other. 



"Advantage was taken of the influence of temperature on the resistance of solu- 

 tions to construct a temperature cell, which is essentially a salt solution inclosed in 

 a hermetically sealed glass tube, in which neither the salt nor the water can change. 

 The solution used has the same temperature coefficient as the soil, so that the vari- 

 ation in the electrical resistance of this cell when buried in the soil, will give the 

 temperature of the soil ; or, if it is used as one arm of the Wheatstone bridge in 

 place of one of the standard comparison coils, it will eliminate the temperature 

 effect altogether in measuring the electrical resistance of the soil. The same cell, 

 therefore, will thus answer a double purpose. 



"For the measurement of the electrical resistance of the soil the Wheatstone 

 bridge method is used with the alternating current and a telephone to indicate when 

 a balance has been obtained." 



The apparatus devised for this purpose is described in detail and 

 the results of observations with the instrument in the field are reported. 



The determination of temperature and soluble salt content of soils 

 by modifications of the same method is also explained. 



"It was desired to perfect a method which would indicate the variations in the 

 soluble salt content in the undisturbed soil of the held, but this has not yet been 

 accomplished, although there is reason to believe it can eventually be done. A very 

 simple and delicate method has, however, been devised for determining the soluble 

 salt content of soils in samples taken from the held. The method consists essentially 



