The Effect of Various Exchangeable Cations Upon the Physical Condition of Soils

The effect of various exchangeable cations upon soil physical conditions was studied using eight soils. The stability of structure and crusting tendency of soils were evaluated by the air‐water permeability ratio and modulus of rupture tests, respectively. The effects of exchangeable magnesium on soil physical conditions were compared with those of exchangeable sodium and potassium, which were previously reported. In addition, the results of similar tests with various combinations of exchangeable sodium and potassium are given. The effect of the various cations on the dispersion and leaching of organic matter was also studied. Although there was a slight increase in modulus of rupture with increasing exchangeable magnesium, the data strongly indicate that exchangeable magnesium and potassium are similar to exchangeable calcium in their effect on stability of soil structure. Combinations of various levels of exchangeable sodium and potassium showed that exchangeable potassium, whether alone or in the presence of exchangeable sodium, had little if any effect in increasing the permeability ratio but reduced the modulus of rupture for several soils. The fraction of organic matter that dispersed and leached from the samples saturated with the various cations was relatively small, and there was no significant difference between the amounts leached from the calcium‐ and magnesium‐saturated soils.