144 Mineral Nutrition of Plants 



tops and roots, and that roots in aerated soils were distinctly more 

 fibrous in character, longer, and more numerous than those from poorly 

 aerated soils. He also found that roots grown in aerated soil had approx- 

 imately twice the surface area of roots on plants grown in nonaerated 

 soil (47). Knight (44) found that artificial aeration of soils increased 

 top and root growth by 30 per cent in pot soil cultures. Baicourt and 

 Allen (5) grew roses in aerated and nonaerated soils. They found that 

 the aerated plants grew 68.4 inches, while the nonaerated plants grew 

 only 37.5 inches in three months. Bushnell (20) aerated the soil in 

 which potatoes were growing by placing a line of perforated tile in 

 the soil. He obtained a yield increase of 15 to 29 per cent for aeration 

 and observed that roots were more abundant around the tile line than 

 in the main body of soil. A somewhat similar result was observed by 

 one of the present authors for heavily watered tomatoes in a com- 

 mercial greenhouse. Here growing roots were found only along the 

 inside surface of the sterilizing tile, or spread out over the surface be- 

 tween the mulch and the soil. Presumably, deficient soil aeration caused 

 by excessive watering prevented normal growth and development of 

 roots in the main body of the soil. 



Several experiments conducted in Ohio established a significant re- 

 lationship between degree of soil aggregation, pore size, and crop yield, 

 particularly on heavy clay soils. A high degree of soil aggregation or a 

 fairly large proportion of larger pores was interpreted as indicating 

 conditions favorable for good soil aeration. Baver and Farnsworth (6) 

 found that, where total air capacity of the soil was only 3 per cent by 

 volume, sugar beets suffered a 50 per cent loss in stand from black root 

 rot disease and yielded only 2-4 tons. Very much higher yields of sugar 

 beets were obtained after the introduction of cropping and manage- 

 ment practices that increased the proportion of coarse pores present in 

 the soil. Where air space porosity was raised, the loss in stand was re- 

 duced to only 10 per cent and the yield was raised to 12 tons. Page and 

 Willard (5^) found a fair degree of correlation between air space poros- 

 ity and corn yield. Rotations that led to increased soil particle aggrega- 

 tion and, hence, better air space porosity and aeration were associated 

 with large increases in corn yields, with average yields measuring from 

 49 bushels in 1936 to 84 bushels in 1945. They concluded that crop yields 



