8 Diseases of Truck Crops 



In studying Table i we find that in every case 

 there is a raarked decrease in soil organisms with each 

 increase in the depth of the soil tested. It was fur- 

 ther found by Brown that the moistture content was 

 higher for four inches than for a greater depth. It 

 seems evident that the decrease of soil bacteria below 

 twelve inches is dependent not so much on moisture 

 but rather on a decrease of air in the lower substratum. 

 It must not be expected that the data given in Table 

 I are applicable to every locality. Differences in 

 the mechanical and chemical composition of the soil 

 and subsoil, differences in topography, climate, and 

 weather conditions, wUl all no doubt tend to influence 

 more or less the increase or decrease of bacteria. 



Influence of Depth of Cultivation on the 

 Number of Soil Bacteria 



The work of King and Doryland* has shown that 

 the depth of cultivation is a potent factor in influ- 

 encing the number of bacteria in the soil. This is 

 briefly summarized by them in Table 2. 



Table 2 

 Influence of Depth of Cultivation on Soil Bacteria 



Silt- 

 plowed 4 inches deep increases the number of bacteria. . 15.46% 

 plowed 6 inches deep increases the number of bacteria . . 10.94% 

 plowed 8 inches deep increases the number of bacteria. .24.20% 

 plowed 10 inches deep increases the number of bacteria . . 26.89% 



» King, W. E., and Doryland, Ch., Kansas Agr. Expt. Sta. Bui. 

 161 : 211-242, 1909. 



