Nitrogenous Fertilizers and Soil Acidity: I. Effect of Various Nitrogenous Fertilizers on Soil Reaction1

Abstract

Studies were made regarding the effect of sodium nitrate, ammonium sulfate, urea, ammonium phosphate, ammonium nitrate, Leunasalpeter, calcium cyanamid, and calcium nitrate on soil reaction. Several different soils were treated in 2-gallon pots in the greenhouse with equivalent amounts of nitrogen in these fertilizers and grown to various crops in succession. The residual effects of these fertilizers on soil reaction were then determined by making studies of the H-ion concentration and the exchangeable hydrogen of the soils. The H-ion concentration data showed that all the nitrogen fertilizers used caused some change in the H-ion concentration of the soils. Sodium nitrate, calcium nitrate, and calcium cyanamid were found to decrease the H-ion concentration. Ammonium sulfate caused the greatest increase in H-ion concentration and was followed in order by ammonium phosphate, Leunasalpeter, ammonium nitrate, and urea. The relative increases in acidity from the use of the various acid-forming fertilizers as indicated by studies of H-ion concentration of the unleached soil were found to be as follows (Table 3): Ammonium sulfate, 100; ammonium phosphate, 51; Leunasalpeter, 65; urea, 28; and ammonium nitrate, 28. After the soils had been leached the relative values were as follows: Ammonium sulfate, 100; ammonium phosphate, 75; Leunasalpeter, 83; urea, 53; and ammonium nitrate, 50. Since the leached soils are believed to represent field conditions more accurately, the relative values obtained from studies on the washed soils are considered to be more reliable. The data obtained from the exchangeable hydrogen study made possible a more accurate comparison of the relative effects on soil acidity of the various nitrogenous fertilizers. The relative increases in exchangeable hydrogen from the use of the various fertilizers on different soils were found to be as follows: Ammonium sulfate, 100; sodium nitrate,--42; urea, 42 tO 50; ammonium phosphate, 100 to 104; ammonium nitrate, 42 to 55; Leunasalpeter, 68 to 76; calcium cyanamid,--55; and calcium nitrate,--39. The relative increases in exchangeable hydrogen from the various acid-forming fertilizers were found to be in good agreement with the relative increase in the H-ion concentration. These values were also found to be in close agreement with the theoretical amounts of acidity that should be developed. Thus, it was calculated from a theoretical consideration that the relative increases in soil acidity from the use of the various acid-forming fertilizers should be as follows: Ammonium sulfate, 100; ammonium phosphate, 100; Leunasalpeter, 75; urea, 50; and ammonium nitrate, 50.