NINTH ANNUAL YEAR BOOK— PART XII 717 
well supplied with carbonate of lime or other bases and mineral foods, 
these bacteria fix considerable atmospheric nitrogen. The amount, of 
course, depends upon the nature and amount of carbohydrate food avail- 
able, the species present, their number and the degree of favorableness 
of the other factors mentioned. In ordinary cultivated soils the supply 
of available carbohydrate materials is the factor that usually limits free 
nitrogen fixation." 
As much as possible crops should be fed on the farm and the manure 
returned to the soil in order to keep up the humus supply. Stock should 
not be allowed to tramp the soil when wet. Neither should the farmer 
cultivate too early in spring or immediately after rains. Erosion of the 
soil should be prevented as much as possible by intelligent methods of 
cultivation, preventing the formation of ditches and keeping rolling land 
covered with vegetation as much as possible. To state the meaning of 
maintaining the physical condition of the soil in a single sentence, I feel 
that I can not do better than use the expression of Henry Wallace, and say: 
"Keeping the soil in good physical condition means keeping it in such 
shape that the growing crops can get the juice out of it." 
FORESTRY FOR THE FARM. 
G. B. BLISS, AMES, IOWA. 
(Before Clinton County Farmers' Institute.) 
The farmer is, in many ways, becoming more and more vitally related 
to the forestry problem. The questions of lumber and fuel supply, protec- 
tion from the winds and heat, climatic conditions, irrigation, water supply 
and other phases of forestry are coming to be of paramount importance 
to agriculture as well as to all other industries of America. 
In the early settlement of this country the question was "How can we 
clear the land of trees most quickly and economically?" Hence a terribly 
wasteful system of forest removal was inaugurated. All over the United 
States forests were hewn down without regard to their value. The timber 
allowed to rot or deliberately burned to get it out of the way, if now 
available would be worth billions of dollars. Yet conditions demanded this 
sacrifice. So the forests, with their enormous resources, had to go. 
Today conditions have changed. Thousands of acres of the very land 
so ruthlessly shorn of its forests in former years is now practically worth- 
less for agricultural crops. The soil has been eroded leaving the rocks 
in conspicuous relief. Corn, tobacco and cotton have been the wealth pro- 
ducers of America but their culture has wrought havoc with the basis of 
Ame-rican prosperity and power, the soil. 
With the scarcity of trees comes the rise in the prices of lumber. Every 
year the farmer pays more for his lumber and hauls out a lighter load. 
Every year the thickness of a board contracts a little. A common inch 
board now seldom exceeds two-thirds to three-fourths of an inch in thick- 
ness. 
There is a constant tendency to force lumber of inferior quality upon 
the market. Brashy and checkered boards, light in weight and with little 
durability are the rule rather than the exception. 
