Plant Soil Environ., 2014, 60(7):325-331 | DOI: 10.17221/202/2014-PSE

Ammonium fixation and release by clay minerals as influenced by potassiumOriginal Paper

H.W. Scherer, E. Feils, P. Beuters

Department of Plant Nutrition, Institute of Crop Science and Resource Conservation, University of Bonn, Bonn, Germany

It is postulated that stabilized ammonium fertilizers improve fertilizer-N utilization by crops, leading thus to higher yields with the same fertilizer rate, especially on sandy soils. However, it must be taken into consideration that in clayey soil at least a part of the NH₄⁺ ions may be fixed by 2:1 clay minerals, thus delaying the effect of the N fertilizer. Because NH₄⁺ and K⁺ have similar size and valence properties and therefore compete for the same non-exchangeable sites of 2:1 clay minerals, we investigated the influence of time and K⁺ application rate on both fixation and release of NH₄⁺. Fixation of NH₄⁺ ions was higher when K⁺ was applied after NH₄⁺, while the influence of the K⁺ application rate was less pronounced. Mobilization of non-exchangeable NH₄⁺ was retarded when K⁺ was applied at the high rate after NH₄⁺. At the first harvest yield formation of ryegrass was neither influenced by the amount as well as the application time of K⁺, because plant available N was not growth limiting, while yield of the second harvest was significantly higher with the low K⁺ application rate after NH₄⁺. After the second harvest the blocking effect of K⁺ on the release of non-exchangeable NH₄⁺ was attenuated and the highest yields of the third cut were reached in the treatments with the high K⁺ application rate after NH₄⁺. Total dry matter yield was highest when K⁺ was applied at the low rate after NH₄⁺. Our results show that K⁺ governs fixation and release of non-exchangeable NH₄⁺, which should be taken into consideration when applying ammonium containing N fertilizers like ammonium sulfate, ammonium sulfate nitrate and ENTEC. Thus K⁺ can affect N availability when N is applied as NH₄⁺ in both the short and long term.

Keywords: nitrogen; availability; potassium; clay minerals; crop yield

Published: July 31, 2014  Show citation