New York Agricultural Experiment Station. 59' 



X. Description of Materials Used as Fertilizers. ' 



1. Forms of Plant-food Essential to Fertilizers. 



In the absence of iron in the soil, plants turn yellow and cease to 

 grow ; other elements, as chlorine, sulphur, etc., are essential to the 

 complete development of a plant. But these elements are used by 

 plants in very small quantities, and, moreover, they occur abun- 

 dantly everywhere in soils, as already indicated. Therefore, it is 

 unnecessary to supply these elements artificially to soils, and we do 

 not need to consider them in connection with fertilizers. The 

 elements of plant-food which experience most often shows to be 

 lacking in soils are these three : 



Nitrogen^ PotassiuTri (contained in ^^otash compounds) and Phos- 

 phoriis (contained in phosphoric acid compounds or phosphates). 



2. Stimulant or Indirect Fertilizers. 



A Stimulant or Indirect Fertilizer is one which does not in itself 

 furnish directly to the soil any needed plant-food, but whose chief 

 -value depends upon the power it possesses of changing unavailable 

 into available forms of plant-food. The stimulant or indirect fer- 

 tihzers which have been most commonly employed are lime, gypsum 

 and common salt. 



Gypsum or Land Plaster, known also as calcium sulphate or sul- 

 phate of lime, has been much used in fertilizing crops. Its value is 

 due to its action as an indirect fertilizer. There has been much 

 difference of opinion as to the manner in which gypsum acts. 

 Probably it acts in at least three different ways, as follows : 



First. It has the power to form compounds with ammonia, in 

 which the ammonia is no longer in danger of loss by evaporation. 

 This power of fixing ammonia is probably of little value when 

 plaster is applied to the surface of the soil, but it may be of much 

 value when scattered over a heap of fermenting manure, and 

 moistened with water, when it will retain the ammonia which would 

 otherwise escape. For the tame reason, plaster is useful to distri- 

 bute about stables, so that it may mix with the manure. 



Second. It has been shown recently that gypsum in some manner 

 aids the process of nitrification, by which ammonia and the nitrogen 

 of organic matter are converted into nitric acid and nitrates. 



Third. Gypsum acts upon the insoluble forms of potash and 

 some other elements of plant-food, converting them into soluble 



