Causes of Diseases in Crops 81 



the crop, the nature of the soil, and the fertilizer 

 applied. In malnutrition the symptoms to be 

 looked for are retarded growth, change of color in the 

 foliage, and root injury. Affected plants remain 

 dwarfed at a time when maximum growth is expected. 

 The color of the foliage turns lighter green, especially 

 in the spaces between the veins (fig. 13) which be- 

 come yellowish green to brown. Roots of such 

 plants are poorly developed, and secondary roots or 

 rootlets are often missing. 



Causes of Malnutrition. The work of Stone 1 and 

 Harter 2 and others seems to have established the 

 fact that malnutrition cannot be attributed to the 

 work of parasitic organisms. Stone cites instances 

 where constant watering with liquid fertilizers or 

 manure would cause malnutrition in cucumber plants. 

 The same is also induced when pig and cow manure 

 are mixed, or when manure is worked into a soil 

 already well fertilized otherwise. Harter records 

 cases of malnutrition brought about by an excess of 

 acidity in the soil. In cabbage fields suffering from 

 malnutrition, it often required from 3500 to 6000 

 pounds of lime to neutralize the excess of the soil 

 acidity. This condition is apparently the result of 

 intensive trucking and the heavy applications of 

 chemical fertilizers which leave the soil acid. Sul- 

 phate of ammonia, muriate and sulphate of potash, 



1 Stone, G. E., Massachusetts Agr. Expt. Sta., Ann. Rept., 5-13, 

 1910. 



2 Harter, L. L., Virginia Truck Expt. Sta. Bui. I : 4-16, 1909 

 (Norfolk, Va.). 



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