Damping-off 



The sudden wilting and death of seedling plants, caused 

 by microorganisms. 



Day-degrees 



The sum of degrees of heat above a threshold, such as the 

 sum of the degrees above a daily mean of 43 F. for the grow- 

 ing season, or for some other period, cf. Temperature sum- 

 mation. 



Day-neutral Plant 



A plant that blooms when the length of day is either 

 long or short, cf. Photoperiodism. 



D. B. H. 



See Breast height. 



DDT 



An Insecticide (q. v.), dichloro-diphenyl-trichlorethane. 



Dealkalization 



Removal by leaching or by chemical treatment of ex- 

 changeable sodium from the soil. cf. Alkali soil. 



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