16 Diseases of Truck Crops 



teids. The sulphur may be further changed into 

 sulphur dioxide, and, when combining with water and 

 oxygen, into free sulphuric acid. The latter read- 

 ily combines with calcium or magnesium, forming 

 calcium or magnesium sulphate. The plant obtains 

 sulphur for the construction of its proteids from some 

 of the soluble sulphates. 



How to Maintain the Fertility of Soils 



We have already seen that the fertility of a soil is 

 directly dependent upon the activity of certain bene- 

 ficial bacteria. The latter constitute the life of a soil. 

 It is therefore evident that for a soil to produce its 

 maximum, its germ flora must receive careful con- 

 sideration at the hands of truckers and gardeners. 

 We must at any cost encourage these organisms to 

 do their full duty at all times. Should they cease 

 activity the soil would become barren. 



There is no doubt that plants remove large quan- 

 tities of plant food from the soil. Headen 1 has cal- 

 culated that for 80,000 tons of sugar beet, there are 

 consumed as fertilizers, 331 tons of potash, worth 

 $31,100; 71 tons of phosphoric acid worth $5,680; 

 160 tons of nitrogen worth $54,400, making a total 

 of $91,180, or a trifle over one dollar per ton. What 

 is true for the sugar beet is true for every other 

 trucking crop. In other words, soil fertility is capa- 

 ble of being exhausted. Most of it may be returned 

 in the form of manure and chemical fertilizers, but 



1 Headen, W. P., Colorado Agr. Expt. Sta. Bui. 99: 3-16, 1905. 



