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

Agelda AJAZI^1*, Liri MIHO², Aida BANI¹, Ardian MAÇI¹

1Agro-Environmental Department, Faculty of Agriculture and Environment, Agricultural University of Tirana, Albania

2Center of Agricultural Technology Transfer, Lushnjë

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Abstract: 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 wasconducted 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 cationshowed that the NH₄⁺ in BCg horizon was fixed in greater quantities than in Ap horizon.

Key words: non-exchangeable NH₄⁺, ammonium fixation, clay minerals