CLIMATIC FACTORS 



65 



of corn. For a yield of 50 bushels per acre, this equals 

 7 to 10 acre-inches of water.^ With a larger crop the water 

 used would be increased proportionally. Under field condi- 

 tions there must be added to this whatever loss may take 

 place through run-off, evaporation from the soil, and 

 seepage. King found that a yield of 7000 to 8000 pounds 



Fig. 24. — Chart showing relation between storage water in the soil and 

 consumption of water by the corn plant each month. The storage 

 capacity of the soil is exhausted before the end of July. The crop is 

 therefore dependent on July and August rainfall. 



of dry matter per acre (approximately a 50-bushel yield) 

 required about 12 acre-inches under field conditions. In 

 this case the loss by seepage, run-off, and evaporation 

 must have been about 5 acre-inches (assuming 7 inches 

 used by the crop) , but this will vary with the soil, culti- 

 vation, distribution of rainfall during the growing season, 

 and amount of storage water in the soil at planting time. 



1 Montgomery, E. G. Ann. Rpt. Nebr. Agr. Exp. Sta. 1901 

 King, F. H. Ann. Rpt. Wis. Agr. Exp. Sta. 190'£ : 99. 

 F 



155. 



