98 Diseases of Greenhouse Crops 



excess of acidity in the soil. In soils where plants 

 suflFer from malnutrition, from 3,500 to 6,000 

 pounds of lime per acre area are often required to 

 neutralize the excess of the soil acidity. This con- 

 dition is apparently the result of intensive trucking 

 and the heavy application of chemical fertilizers 

 which leave the soil acid. Sulphate of ammonia, 

 muriate and sulphate of potash and acid phosphate 

 when used continuously will leave the soil in a very 

 acid condition. On the other hand, nitrate of soda, 

 carbonate of potash and Thomas phosphate tend 

 to make the soil alkaline. 



Another important cause of malnutrition is the 

 exhaustion of humus. This is a natural result where 

 commercial fertilizers are used instead of some form 

 of organic manure. 



Methods of Controlling Malnutrition. It is quite 

 obvious from what has already been said, that the 

 greenhouse grower is the loser if he uses his fertilizer 

 injudiciously. Not only is malnutrition favored by 

 such a course, but the yields, too, are considerably re- 

 duced. With acid soils, liming to neutralize the soil 

 acidity will help control malnutrition. 



Chlorosis 



This disease may be attributed to several causes. 

 Greenhouse plants that receive too much shade will 

 become yellowish, then whitish, and in time may 

 lose all their green color and finally die. Chlorosis 

 is often brought about when plants grow in soils 



