Jan. 2,1917 
Availability of Potash in Orthoclase-Bearing Soils 
27 
allowed to grow for varying periods, ranging from 5 to 12 days. Plant 
samples were then withdrawn and analyzed for potash by the official 
method. Table VIII shows the treatment and the percentage of potas¬ 
sium oxid in each lot of plants, expressed in terms of the dry weight. 
Table VIII .—Potash absorbed by wheat seedlings from orthoclase and soil solutions as 
affected by calcium sulphate. 
Series 
No. 
Treatment. 
Percentage 
of potassi¬ 
um oxid in 
dry plants. 
I 
10 gm. of orthoclase, 2,500 c. c. of carbon-treated water. 
Same, saturated with calcium sulphate.. 
I. 19 
I 
•95 
2 
10 gm. of orthoclase, 2,500 c. c. of carbon-treated water... 
Same, saturated with calcium sulphate. 
1. 84 
2 
1. 72 
3 
40 gm. of orthoclase, 2,400 c. c. of carbon-treated water plus 200 
2. 56 
p, p. m. N 0 3 and 200 p. p. m. P 2 0 5 . 
3 
Same, saturated with calcium sulphate. 
2- 57 
4 
50 gm. of Oatman soil, 2,500 c. c. of carbon-treated water. 
Same, saturated with calcium sulphate. 
i -75 
4 
i -35 
The period of growth was varied so that the dry weight of the plants 
in the different series was not the same, which accounts for the differ¬ 
ences in the potash content of the various cultures when expressed in 
percentage of the dry weight. In the third series 200 p. p. m. of N 0 3 
as NaN 0 3 and 200 p. p. m. of P 2 0 5 as Na 2 HP 0 4 were added to balance 
the nutrient solution. 
To insure the solution of the potash, the solutions containing finely 
ground orthoclase in series 3 were shaken up for four days before they were 
used for culture purposes. Analyses of the resulting solutions at the time 
the cultures were started showed 9.6 p. p. m. of potassium oxid where 
gypsum was absent and 6 p. p. m. where gypsum was present. Such 
potash concentrations are sufficient for the nutrition of plants, as the 
potash content of the soil solution in humid soils seldom exceeds 10 
p. p. m. It will be shown in another paper that wheat plants can 
readily take up potash and other salts in concentrations of 1 p. p. m. 
or less. 
If the calcium sulphate had liberated any additional potash from the 
feldspar, the seedling plants would have taken it up, and this would 
have been shown by an increase of the potash content of the plant ash. 
In none of the three series of cultures, however, was the potash content 
of the plants increased by the addition of gypsum to the solution. 
In the Oatman soil (series 4) the addition of gypsum decreased the 
absorption of potash by plants. It will be recalled that the analyses of 
the solutions also showed that the use of gypsum depressed the solu¬ 
bility of the potash in this soil (Table VII). 
