THE WILTING COEFFICIENT FOli PLANTS IN ALKALI SOILS. 



19 



been absolutely, as well as relatively, richer in calcium and magne- 

 sium, but both absolutely and relatively very much poorer in sodium, 

 in chlorids, and especially in sulphates. Soil No. 78 is also relatively 

 richer, although absolutely poorer, in potassium and bicarbonates. 



In order to insure as nearly as possible the same percentage of water 

 available for growth in all soil mixtures used in the experiment, suf- 

 ficient water was added to each stock soil to give them practically the 

 same "available" moisture content. The total water contents at- 

 tained were 24.4 per cent in soil Xo. 78 and 23.9 per cent in soil No. 

 79, which gave available-water contents of 10.6 and 10.8, respectively. 



PREPARING THE SOIL MIXTURES. 



It was decided to use in the experiment stock soil No. 78 and 14 

 mixtures of the two stock soils. A graduated salt content in these 

 mixtures was obtained by varying the proportions of the two stock 

 soils. Precautions were taken to reduce evaporation to a minimum 

 during the mixing and subsequent handling of the soils. Determina- 

 tions of the electrical resistance (in ohms, at 60° F.) and of the total 

 water-soluble material, moisture equivalent, and moisture content (in 

 percentages of dry weight of soil) were made upon each mixture as 

 prepared for planting. These values, together with the initial con- 

 centration of the soil solution (calculated from the total water-soluble 

 material and the initial water content) , the wilting coefficient (calcu- 

 lated from the moisture equivalent), and the percentage content of 

 water available for growth (by subtraction of the wilting coefficient 

 from the percentage of total water present) are given for each of these 

 mixtures in Table II. 



Table II. — Electrical resistance, total soluble material, concentration of solution, mois- 

 ture equivalent, uniting coefficient, moisture content, and moisture available for growth 

 in the soil mixtures used (means of all determinations) . 



1 Since the percentage of moisture corresponding to the wilting coefficient for the 15 soils averaged 56 per 

 cent of the percentage representing the initial moisture content and since there was little change in the 

 total salt content of the soils (as shown by determinations of electrical resistance) during the period of the 

 experiment, it follows that the concentration of the solution in each soil had very nearly doubled when 

 the wilting coefficient was reached. 



2 There was evidently an error here, either in taking the sample or in the determination. 



[Cir. 109] 



