148 Plant Physiology 



sulfate, sodium nitrate, and some other salts are injurious 

 when applied to seed in pure sand. Newman 1 concluded 

 that on sandy soil 400 pounds of sodium nitrate is unfavor- 

 able to the germination of peas. Hicks, 2 reporting upon 

 the germination of seeds as affected by diverse fertilizers, 

 states that, "commercial fertilizers should not be brought 

 into direct contact with germinating seed." 



80. The forms of the nutrient compounds. Since the 

 mineral nutrients (including nitrogen) are available to the 

 plant usually only through the soil solution, it is a general 

 rule that any soluble inorganic salts which are not toxic, 

 or poisonous, may supply the nutrient or nutrients needed. 

 Nitrogen, for instance, in water cultures may be supplied 

 in the form of any of the nitrates. In the field it could not 

 be supplied either as calcium or magnesium nitrate, on 

 account of the greater expensiveness of these compounds. 

 It may be supplied as potassium nitrate, saltpetre ; but 

 more extensively as sodium nitrate, or Chilian saltpetre, 

 a common fertilizer. Again, nitrogen is to a certain extent 

 supplied as ammonia compounds, the compound of prac- 

 tical importance being ammonium sulfate. Ammonium 

 compounds are further readily diffused through the soil, 

 and if not used directly, they are, by microorganisms, 

 easily converted into nitrates ; hence they may be con- 

 sidered, in general, as readily available forms of this the 

 most expensive of the nutrient elements. In this connec- 

 tion it is important to note that it is only after decompo- 



1 Arkansas Agl. Exp. Sta., Bui. 34 : 99-124. 



2 Hicks, G. H., "The Germination of Seed as Affected by Certain 

 Chemical Fertilizers." Div. Bot. U. S. Dept. Agl., Bui. 24 : 15 pp., 2 pis., 

 1900. 



