376 
THE ECONOMIC ASPECTS OF SOIL EROSION 
should be made as deep as it well can be. The void spaces in 
the ground which is overturned to the depth of ten inches will if 
the earth be ordinarily dry take in a rainfall of an inch or per- 
haps an inch and one-half in depth falling in, sa}", two hours, 
without au}^ surface flow; while if the depth of the tillage be but 
five inches half the water would have to pass over the surface. 
The well-known, but unhappily little used, ])rocess of subsoil 
plowing if discreetly used is also a valuable means of effecting 
the penetration and storage of water; underdraining also tends 
to the same end. In certain parts of the southern states of this 
countrv, where the evil effects of the surface flow have forced 
themselves upon the attention of the ])eo])le, the farmers have 
begun to guard against the destructive action of this agent liy 
forming temporary benches in the sloping fields. In the Old 
W'orld the system of benching the hillsides is carried much farther 
than it is in any part of this country. In Germany, France, and 
Italy the greater }>art of the land that lies on steep declivities 
which have not been brought to ruin in the earlier and less 
conservative agriculture is now protected from destruction. Al- 
though we may ex{)ect a constant gain in the api)lication of this 
conservative treatment of our fields, we cannot look to it alone 
for their safeguarding. Another class of ])recaution demanded 
b\" the elemental conditions of this country must be taken, and 
that we will now note. 
Owing to the fact that in North America generall}^ the rain- 
fall is apt to have a torrential character (the ])recipitation taking 
■])lace at a rate which is not common in Europe) and to the fact 
that these downpourings are likely to occur on ground which 
has been loosened by the frost, our soils are exposed to a meas- 
ure of danger much greater than that which menaces the fields 
of the. Old World. There appears to be but one way by which 
we ma}^ meet this danger — this is by limiting the work of the 
plow to those fields which have a degree of slope so slight that 
with i)i’oi)er tillage they may not be exposed to scouring action. 
Although this classification has to be made for each district and 
species of soil, it may in general be said that no field which has 
a greater sloi)e than five feet vertical in one hundred feet of 
length should in any countiy be exj)Osed to the danger which 
ordinary cropping inflicts. Areas from this measure of inclina- 
tion upward to thrice this rate of slope, or to a maximum of 
fifteen feet in the hundred, may reasonably be ]fiowed in order 
to bring them into the state of grass lands, but should not be 
