236 THE CEREALS IN AMERICA 



(3) Weeds evaporate water. The demand of the maize 

 plant for water is so great at certain periods of its growth that 

 the possibility of development and yield is fixed by the supply 

 of water available. (280) If this supply of water is in any way 

 reduced by the growth of weeds, the yield of maize must be 

 reduced. Sturtevant observed the difference in practice among 

 the vineyardists in New Jersey. Those on the low lands allow 

 weeds to grow : on the uplands the soil is kept free of weeds. 

 The inference is that the weeds pump the water out of the wet 

 land to the advantage of the grape, which prefers a dry soil. 



310. The Effect of Stirring the Soil is to break the roots in 

 the area stirred and to make the soil in this area looser, other- 

 wise change its structure and to bring particles of soil into dif- 

 ferent relations one to another. This allows air, water and 

 roots to enter more freely. The amount of water, the tempera- 

 ture, and probably the salts in solution are. affected thereby. 

 (297) King found that cultivating three inches deep made the 

 soil .4 to 1.1° F. cooler than cultivating 1.5 inches deep.^ 



311. Root Pruning. — It has been clearly demonstrated that 

 any mutilation of maize roots has an injurious effect. At th(i 

 Illinois Station ^ pruning three to four times during the ordinary- 

 season on all sides six inches from the center of the hill to a 

 depth of four inches reduced the yield of grain from ten to thirty- 

 two per cent, the average decrease for five years being twenty 

 per cent. The greater percentages of decrease were during 

 seasons of least rainfall. Pnming three inches deep one season 

 caused a decrease of five per cent. The Oklahoma Station^ 

 found during one season no injury from running a knife three 

 inches deep six inches from the hill, or six inches deep twenty- 

 two inches from the hill, but when the knife ran six inches deep 

 six or twelve inches frotn the hill the yield was much reduced 



1 Wis, Rpt. 1893, P- ^9°> 1^94' P- 283. 

 8 IlL Bills. 13, 25, 31. 

 8 Okla. BuL 36. 



