Distribution of Fixed Ammonium in Soils
1959
Stevenson, F. J. | Dhariwal, A. P. S.
Fixed ammonium was determined in 17 profiles representative of most of the great soil groups occurring within the North Central Region of the United States. The results showed that a vast reservoir of N exists in the terrestrial areas of the world as ammonium held within the lattice structure of clay minerals, thereby revealing a heretofore missing link in the N cycle. The amount of fixed ammonium in the soil was found to depend upon the type and amount of clay minerals present. With respect to clay mineral type, the order was illite > montmorillonite > kaolinite. Drainage, type of vegetative cover, and extent of leaching of the profile by percolating water had little effect on the fixed ammonium content of the soil. Cropping decreased the amount of fixed ammonium in surface soil; however, the fraction of the N present as fixed ammonium was greater for cropped soil than for uncropped soil.
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