34 



Diseases of Truck Crops 



TABLE 6 (Continued) 



We have as yet no definite data on the effect of lime 

 on peaty soils. Those in charge of the development 

 of peaty soils caution against using it too freely. Of 

 the forms to use, ground limestone or marl are per- 

 haps the best kinds to apply. The amount to use 

 will vary from one to four tons, depending largely on 

 the acidity of the soil. Too much lime tends to de- 

 stroy the nitrogenous compounds, and encourages 

 serious plant diseases. 



5. ALKALI-SICK SOILS 



The alkali problem is even of more widespread 

 concern, as it affects nearly all irrigated districts 

 of the arid and semi-arid regions of the United 

 States. An alkali-sick soil is one which contains 

 an excess of accumulated soluble salts which are 

 injurious to plant growth. For convenience, 

 alkali soils are divided into black and white. The 

 black alkali lands are known to contain sodium 

 carbonate or washing soda as the essential salt. The 



