Missouri Corn Growers' Association. 345 



untreated plots. It would seem then to be a good practice on 

 large farms where long rotations are used to apply the manure to 

 the grass crops in the latter years of the rotation, 



INFLUENCE OF RAINFALL. 



Water is the most important food of the corn plant and 

 upon its supply the yield of the crop depends more than upon 

 any other factor. Crops suffer each year from too much as well 

 as too little moisture. The draining of wet lands both by sur- 

 face and underdrainage and the construction of dikes and levees 

 to prevent overflows is each year increasing the acreage of land 

 on which corn may be grown. At the same time it may be said 

 that the corn crop as a whole suffers more from a deficiency of 

 water than from an excess, and one of the most important factors 

 influencing the yield of corn is that of rainfall. 



The rainfall in the corn belt during the months of June, 

 July and August has been found to be closely correlated with the 

 yield of corn. This is especially true of the month of July. 

 Although the average rainfall in most sections of the corn belt 

 ranges from 30 to 40 inches, there is hardly a season passes that 

 in some sections the yield of corn is not seriously cut by insuf- 

 ficient rainfall. This was especially well illustrated in Missouri 

 during the past year. The State experienced one of the most 

 severe drouths in its history and one of the lightest corn crops 

 on record was produced. Yet the total rainfall for the season 

 was not far below normal. It is not the total rainfall of the year 

 then that cuts the yield of our crops, but rather its unequal dis- 

 tribution. It has been found that from 14 to 20 tons of water 

 are required to produce one bushel of corn. This equals from 

 7 to 14 surface inches for an average crop of 50 bushels. To this 

 must be added the loss from seepage runoff and surface evapora- 

 tion which under field conditions is sufficient to bring the total 

 water requirement up to from 12 to 14 inches. 



An average corn soil in good tilth will store about five or 

 six inches of available water in the upper four feet. A 50-bushel 

 crop of corn would then require at least six inches additional 

 rainfall during the growing season, and probably even more than 

 this, for the plant's growth would be checked before it had ex- 

 hausted the soil moisture to low limits. A 75-bushel crop would 

 require an additional rainfall of at least ten inches and a 100- 

 bushel crop fifteen inches during the growing season. On rolling 



