336 Diseases of Greenhouse Crops 



Table 17 a 



Average Composition of an Overfed Soil Com- 

 pared to a Normal Soil 



Pounds per Acre 



Normal 

 SoU 



Overfertilized 

 SoU 



Total water soluble salts . . . 



Soluble nitrogen 



Soluble pota^ 



Soluble phosphoric acid. ... 

 Soluble calcium oxide (lime) 



Soluble magnesium oxide 



Soluble sodium oxide 



12.874 

 209 



2-433 



traces 



580 



369 

 972 



15- 193 



91 



2-957 



traces 



657 



435 



1.923 



plant could stand. It further indicates that a large 

 amount of horse manure was used in this particular 

 case. 



Control. It seems that the average greenhouse 

 beds are faulty in construction. One of the main 

 requisites is to provide good drainage. This is far 

 more important in the greenhouse than in the open. 

 Crops need plant food. A slight excess is desirable 

 to force quick growth. An overdose of horse ma- 

 nure or chemical fertilizers will produce more harm 

 than good. No guesswork should be permitted to 

 take the place of accurate calculation in applying 

 fertilizers. The surface area of the greenhouse bed 

 may be easily expressed in terms of acreage. Sup- 

 pose that 500 pounds of sulphate of potash is re- 

 quired per acre (4,800 square yards), then in the 

 greenhouse 1.6 ounces would be required per square 

 yard. In this way, all fertilizers may be applied 



