Author:
HW Scherer,Feils E.,Beuters P.
Abstract
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 NH<sub>4</sub><sup>+</sup> ions may be fixed by 2:1 clay minerals, thus delaying the effect of the N fertilizer. Because NH<sub>4</sub><sup>+</sup> and K<sup>+</sup> 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<sup>+</sup> application rate on both fixation and release of NH<sub>4</sub><sup>+</sup>. Fixation of NH<sub>4</sub><sup>+</sup> ions was higher when K<sup>+</sup> was applied after NH<sub>4</sub><sup>+</sup>, while the influence of the K<sup>+</sup> application rate was less pronounced. Mobilization of non-exchangeable NH<sub>4</sub><sup>+</sup> was retarded when K<sup>+</sup> was applied at the high rate after NH<sub>4</sub><sup>+</sup>. At the first harvest yield formation of ryegrass was neither influenced by the amount as well as the application time of K<sup>+</sup>, because plant available N was not growth limiting, while yield of the second harvest was significantly higher with the low K<sup>+</sup> application rate after NH<sub>4</sub><sup>+</sup>. After the second harvest the blocking effect of K<sup>+</sup> on the release of non-exchangeable NH<sub>4</sub><sup>+</sup> was attenuated and the highest yields of the third cut were reached in the treatments with the high K<sup>+</sup> application rate after NH<sub>4</sub><sup>+</sup>. Total dry matter yield was highest when K<sup>+</sup> was applied at the low rate after NH<sub>4</sub><sup>+</sup>. Our results show that K<sup>+</sup> governs fixation and release of non-exchangeable NH<sub>4</sub><sup>+</sup>, which should be taken into consideration when applying ammonium containing N fertilizers like ammonium sulfate, ammonium sulfate nitrate and ENTEC. Thus K<sup>+</sup> can affect N availability when N is applied as NH<sub>4</sub><sup>+</sup> in both the short and long term.
Publisher
Czech Academy of Agricultural Sciences
Cited by
24 articles.
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