438 IOWA DEPARTMENT OF AGRICULTURE 



STERILIZATION OF SOIL BY STEAINI 



The soil may be steam sterilized by either the inverted pan or the drain 

 tile method with very satisfactory results. 



Inverted pan method. This method consists of forcing steam under a 

 large pan laid over the soil. The pan is made of No. eighteen sheet iron 

 ten ft. long, six ft. wide, and six in. deep. The top six to eight inches of 

 the soil should be loosened up with a spade so that the steam can enter 

 readily. When the soil is in condition and the pan is in place steam 

 should be forced into the pan for one hour at 75 pounds pressure. A 

 potato buried 6 in. deep in the soil under the pan may be used as an 

 indicator. When this potato is cooked the soil has been sterilized long 

 enough. The source of the steam may be either a greenhouse boiler, a 

 threshing machine engine, or any other type of steam generating machine 

 carrying a pressure of 75 to 100 pounds. 



Drain tile method. This method consists of laying lines of four inch 

 tile in ditches ten Inches deep and two feet apart and ridging up over 

 them the soil to be sterilized. The entire surface of the ridge should 

 be covered with canvas or building paper to confine the steam. Steam 

 at high pressure should be allowed to flow into these lines for about 

 four hours, or until a potato buried in the surface soil of the ridge is 

 cooked. 



STERILIZATION OF SOIL BY FORMALDEHYDE 



This method is very simple and does not dequire a great deal of 

 equipment. It is recommended that a solution consisting of one quart 

 of commercial formalin to twelve and one-half gallons of water be 

 sprinkled on the seed bed with a sprinkling can at the rate of one-half 

 gallon per square foot of soil. Cover the soil with a canvas or heavy 

 paper for twenty-four hours. At the end of this time it should be un- 

 covered and allowed to dry rapidly. It is not advisable to plant cabbage 

 seed in this soil until it has dried out which usually requires a week 

 or ten days in the open. If the seed beds are to be used early in the 

 spring it is desirable to treat the soil in the fall and avoid delay 

 incident to the drying of the soil. 



SOIL INOCULATION. 



By P. E. Brown 

 Soil inoculation is the introduction of certain desirable bacteria into 

 the soil. As a practice it is very old, having been followed many years 

 before its beneficial influence was understood. In reclaiming infertile 

 land, the addition of fertile soil was often found helpful, especially for 

 such crops as clover. The practice did not become general, however, 

 until some thirty years ago when the reason for the soil-enriching proper- 

 ties of legumes was discovered. 



At that time it was demonstrated that when clovers, vetches, alfalfa, 

 cowpeas and all other legumes are associated with certain bacteria, 

 these crops have the power of taking nitrogen from the air for their 

 growth. It was demonstrated further that if the bacteria we "e intro- 



