CHAPTER IV 

 MANURES, LIME AND FERTILIZERS 



Need of plant food. Greenhouse vegetable forcing is 

 the most intensive type of agriculture. The plants are set 

 very close together, so that a maximum draft is made on 

 the supply of available plant food. One crop follows 

 another in close succession, and in a well-managed house 

 there is practically no loss of time or space from Sep- 

 tember 1 to August 15. Continuous heavy cropping 

 under glass requires much more plant food than any line 

 of outdoor cropping that can be followed in temperate 

 regions. 



Again, the greenhouse vegetable grower raises products 

 of high money value, and the cost of the plant food re- 

 quired for maximum crops is so insignificant, compared 

 with the net returns, that he cannot afford to take chances 

 by not supplying sufficient nourishment. It is not un- 

 common to see greenhouses which are properly heated 

 and ventilated filled with crops that are small and inferior 

 because the plants have not been properly fed and per- 

 haps watered. There must be perfect cultural conditions 

 in every respect in order to realize the utmost returns. 

 No greenhouse soil has yet been found which does not 

 need frequent and liberal applications of plant food. 



Value of manures. Numerous investigations have 

 shown that the crop-producing power of a soil is more 

 dependent upon its physical than upon its chemical 

 composition. In other words, if a soil possesses the best 

 physical properties, plant foods are not likely to be want- 

 ing to any considerable extent. The probabilities are 

 that this conclusion of the soil specialists does not apply 

 so much to the artificial conditions of the greenhouse as it 



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