Jan. 7, 1918 



Studies in Soil Reaction 



25 



EFFECT OF FERTILIZER MATERIALS ON SOIL REACTION 



It has frequently been stated that certain fertilizer materials, more 

 especially ammonium sulphate and acid phosphate, increase the acidity 

 of soils. To obtain additional evidence, the H-ion concentration of 

 soil suspensions have been measured in samples taken from the ferti- 

 lizer plots of the North Carolina Experiment Station. Some of the 

 soils have received annual applications of these fertilizers for as many 

 as 15 years. All fields are located on well-defined soil types for each 

 area of the State. Three distinct types have been studied. 



The samples of both soil and subsoil were collected as carefully as 

 possible. Borings were made at several points on the plots for both 

 surface and subsoil samples. These were taken to the laboratory as 

 quickly as possible and thoroughly mixed, after which water was deter- 

 mined in each composite sample. The ratio of water to soil was kept 

 the same as with the air-dried soils. 



Table III gives a compilation of the total amount of each fertilizer 

 material and lime which has been applied to the plots at the different 

 branch stations. 



Table III. 



-Total quantity {in pounds per acre) of fertilizer materials applied to 

 experimental plots 



The data secured from the measurements of the H-ion concentration 

 of plots fertilized with ammonium sulphate and sodium nitrate are given 

 in Table IV. 



Marked increases in acidity can be noticed in samples taken from plots 

 fertilized with ammonium sulphate. In every case pronounced increase 

 of H ions is evident, and extends to the subsoil in all of the fields studied. 

 On the Norfolk fine sandy loam more acidity is noted in the subsoil than 

 surface. 



There does not appear to be any relationship between texture and 

 development of acidity by ammonium sulphate. This is in agreement 

 with the work of Allison and Cook (/). 



The results secured from the sodium-nitrate plots are in harmony with 

 the accepted theory regarding its effect on soil reaction. A reduction of 

 acidity is apparent. 



