560 IOWA DEPARTMENT OF AGRICULTURE, 



it has good color, the stalks are strong, but the ears do not fulfill the 

 promise of the early part of its history. The result seems to indicate 

 that clover restores only a part of the material necessary to produce corn. 

 What can we do now? How can we discover the source of our trouble? 



Chemical analysis shows that corn is composed mostly of potash, 

 phosphorous and nitrogen, hence it is a fair supposition that to produce 

 corn the soil must contain these elements in sufficient quantity and in 

 relative quantities or proportion. A crop of any grain to give best re- 

 sults needs a balanced ration just as much as a steer does to make a good 

 growth and gain in weight. So we assume that we must have a sufficient 

 amount in our soil of these necessary elements of fertility, viz, potash, 

 phosphorous and nitrogen. Of these elements the ultimate source of sup- 

 ply of nitrogen is the air, it being in large part composed of nitrogen. 

 The other elements, the potash and phosphorous, are of a mineral nature 

 and exist only in the earth. Hence, if we use a crop of clover to restore 

 fertility, the only possibility of making an increase of the quantity of 

 the elements of fertility in the soil must lie in what it can derive from 

 the air. If it has any other effect it can only be that of making more 

 available what is already in the soil, unless it possesses creative power, 

 which no one will assume. 



The effect of clover on a corn crop seems to be a stronger growth, 

 darker color, larger stalks, larger ears with unfilled tips, and later ripen- 

 ing, but not a return to the desired yield of grain. We can fairly and 

 safely assert this change in the crop to be the result of an increased 

 supply of nitrogen but it does not meet our wishes. We want more ker- 

 nels. 



We have now exhausted the possibilities as to a gain from the air, 

 and it begins to look as if the deficient factor in the problem must be 

 one of the mineral elements of fertility, and the thing to do seems to be 

 to learn which one is needed if happily both are not in scant supply. If 

 we turn our attention directly to our soil and interrogate it as to its 

 wants, we shall find that an application of potash gives it but little help, 

 so the answer from the soil would seem to be — I have enough of that. 

 At this stage of the inquiry the conditions strongly suggest that the 

 wanted factor in the problem is phosphorous. How shall we verify this 

 hypothesis? What do we know about it? Not very much, I fear. So 

 far as I know, no thorough and reliable analysis has ever been made of 

 our prairie soil, and we do not know what elements it contains, or the 

 relative quantity of either element. It must contain some of each ele- 

 ment or it would not produce a crop, but the diminishing yields under 

 cultivation indicate that some element is not present in sufficient quan- 

 tity, and that the deficient element may be phosphorous. The only ap- 

 parent source of information seems to lie in the geological history of 

 this region. We are told that in the remote past a sheet of glacial drift 

 covered all this part of Iowa. Later on another glacial deposit of great 

 depth entirely covered the first one, and this last sheet makes our sur- 

 face soil. Now if we can find where this later drift came from, or of 

 what it was made, we can formulate a plausible conjecture of the com- 



