Ammonium fixation by some soils in the ussr and the availability of this ion to plants

Summary

The ability of various soils to fix ammonium in unexchangeable form was studied. Soils in their natural state contain unexchangeably fixed NH₄. The amount of which considerably increases with systematic fertilization and in soils with high nutrient status, but the ability of these soils for extra fixation of ammonium decreases. Chernozem soils are able to fix ammonium in unexchangeable form in considerably greater quantities than soddy-podzolic soils. All soils show a little increase of ability to fix ammonium with profile depth. The heavier is the soil the greater is its ability for fixation of NH₄ in unexchangeable form.

In the conditions of a greenhouse experiment unexchangeably fixed NH₄ was used by plants very poorly. Exchangeably absorbed ammonium is available to plants, although to a lesser extent than water soluble salts. Soils fix ammonium to a greater amount from NH₄OH than from ammonium nitrate, hence the latter is a better source of nitrogen for plants than ammonia liquor solution if applied to soils with a definite abolity to fix unexchangeable ammonium.