12 
BULLETIN 83. 
low that it must be present in the soil in an ordinary aqueous 
solution. But when present as such it is capable of being taken 
up by the plants. The most important mineral substances that, 
the plants need are potash, lime, phosphoric acid, chlorin, sulfur 
etc. The one used in the largest quantity by them is potash. 
The total quantity of this substance in our average good soil is 
probably not far from 40 tons to the acre taken to the depth of one 
foot; the percentage of this available is small and the form in 
which the available portion is present is doubtful. The rest is 
present principally as a felspar. It has long been known that the 
water attacks this mineral and I have shown that the oat plant 
can obtain potash from it if it has been finely powdered. The 
question whether the water in the soil dissolves this element of 
plant food out of the felspar is important. While we can argue 
that it must do so we want to know that it does, and how fast. 
We can not always obtain all the information that we desire but 
we have tried to find out how much potash was present as a free 
solution in the soil, or better, how much potash was contained in 
this water after it had entered the soil. An acre-foot of water, as 
applied to the field, contained almost 12 pounds of potash. A like 
amount of water as it was found in the soil after irrigation con¬ 
tained 18 pounds, a definite gain of six pounds per acre-foot of 
water. This is not a large amount of potash to be gathered by 
this amount of water but it serves to show positively that work is 
being done by this water, for it is richer by six pounds of potash 
than it was before. This problem is not so simple as it seems and 
there is much more involved in it than is here stated. But the 
fact as here stated is near the truth in spite of the many things 
that are left out of consideration. There is in it an abundance of 
chlorids and sulfur as sulfates to supply the plants with these ele¬ 
ments. 
I have not been able to find that it plays any direct part in 
supplying the plants with phosphoric acid. These statements 
show that the water within the soil is an active agent working 
constantly in behalf of the plants, but there is other work that it 
does, likewise beneficial to the plant but less directly so. 
The water brings potash into solution within the soil but 
owing to certain properties of the soil particles it is not able to 
carry it out except in smaller quantities. I have tried to show 
that the water draining out of the soil carried the sodic carbonate 
out more readily than it does the sulfate, and I will now add that 
it seems still more difficult for it to carry out the potash. We 
have stated that the irrigation water carried 12 pounds potash per 
acre-foot and the ground water 18 pounds, taking the average of a 
good many ground waters we get 20 pounds per acre-foot. The 
drain waters carry only about five pounds per acre foot. The 
