Effect of potassium on fixation of ammonium by clay minerals in different soil layers

In intensive agriculture systems, efficient nutrient use is necessary for high crop yields as well as for sustainable environment management. Fixation of NH4+ and K+ by soil clays affect N and K availability to plants. Latest studies indicates that non-exchangeable NH4+, may affect crop productivity and soil N dynamics more than previously thought. An incubation study with K2SO4 and NH4NO3 was conducted to evaluate NH4+ and K+ fixation in two southern Albanian soils. Soils contained significant amount of native-fixed NH4+ and showed relatively high NH4+ fixing capacity. Native fixed ammonium content varied for horizons Ap and BCg, from 97 to 133 mg/kg and accounted for between 5 to 19, 8 % of the total nitrogen, respectively . Ammonium fixation was increased with N rates and was reduced with increased K rates. When K was added to the soil prior to the NH4, the amount of ammonium fixed was reduced. By contrast, when K+ and NH4+ were added to the soils simultaneously (equivalent amount; 2mEq/100g), the ammonium fixation was increased somewhat in the BCg horizon , whereas no such preference for ammonium fixation was found in the Ap horizon. In case when NH4+ and K+ were added to the soil samples in form of solutions, containing equal amounts of NH4+ (corresponding to 2 mEq NH4+/100 g soil) but varying amounts of K+, the capacity of the soil to fix ammonium was reduced in proportion to the amount of K+ added. The soil samples incubated anaerobically, were with high differences in clay minerals content. The dominate clay minerals for profile (I-Ap horizon) are smectite > vermiculite > Ilite, while vermiculite plus ilite (as the most important clay fixed minerals), comprised 21% of clay fraction and 13 % of the soil. In the profile (II-BCg horizon), the dominant clay minerals ranged; vermiculite > Ilite > smectite, while (vermiculite + ilite), comprised 52% of the clay fraction and 23, 4 % of the soil. Studies on Ap and BCg horizons comparing the amount of NH4+ fixed for equivalent of amount of added cation showed that the NH4+ in BCg horizon was fixed in greater quantities than in Ap horizon.