SOILS. 



29 



sections to a depth of -i ft. on plats of medium ela}' loam soil having 

 clay subsoil changing to sand at a depth of 4: ft. The soil had been 

 in pasture during- 1800 and 1897 and bore a crop of rape in 1898, no 

 fertilizers or manure having been used during this interval. The soil 

 was plowed, rolled, and harrowed on May 23 and was cultivated 

 weekly thereafter until September 1.5. It was kept fallow and free 

 from weeds. 



The methods used in making the determinations are described. For 

 the soluble salts Whitney's electrical apparatus was employed (E. S. R., 

 9, p. 535). In every case, however, "the amount of dry soil and of 

 moisture in the cell was determined by weighing the cell full before 

 each determination, and then, after measuring the resistance, emptying 

 the contents into the trays, drying the soil, and from the percentage 

 of water calculating the amount of water and of dr^^ soil which occupied 

 the cell when eaeh resistance was measured." 



The formula used with the electrolytic soil in these observations was 



W^ 



A = 0.00 



R S 



where A is the per cent of soluble salts in the dry soil expressed as 

 sodium chlorid, W the amount of water in the cell, li is the observed 

 resistance at 00" F., S is the amount of dry soil in the cell, and 0.00 is 

 a consta t whose logarithm is 0.782501. 



Observations were made at 4 different dates to determine the changes 

 in the solul)le salts in the soil with the following results: 



Tlicmcan cJidnyc in. mtlnlilc nalt.i conijiided af< sodium chlorid in. fallow yround between 

 May 24 and September 15. 



"The mean gain of soluble salts, and presumably of plant food also, has taken place 

 most rapidly in the surface foot, the increase being more than double that in the 

 second foot, nearly 7 times that in the third, and 12 times that in the fourth foot. 



"The total mean gain in soluble salts per acre in the upper 4 ft., as indicated by 

 tlio method, was 397.1 lbs., and tlie total amount at the end of the season in the root 

 zone was 1,073.5 lbs. per acre." 



Observations on th(» influence of different depths and frequencies of 

 tillage on soluble salts of the soil indicate "that the largest increase 

 in the amount of soluble salts occurred in the surface foot of the fal- 

 low plat not cultivated, the final gain between May 24 and September 

 15 being 533 lbs. per acre, which is 2.6 times the mean gain which 

 occurred in the surface foot of the cultivated soil." The surface foot 

 of plats cultivated once in 2 weeks gained more than that of plats 



