Ammonium fixation by clay minerals in different layers of two paddy soils after flooding

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.

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Clay Minerals of Paddy Soils in Taihu Lake Region

Proceedings of Symposium on Paddy Soils ◽

10.1007/978-3-642-68141-7_56 ◽

1981 ◽

pp. 480-485

Author(s):

Xu Ji-quan ◽

Yang De-yong ◽

Jiang Mei-yin

Keyword(s):

Clay Minerals ◽

Taihu Lake ◽

Paddy Soils ◽

Lake Region

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An evaluation of naturally occurring fixed ammonium in soils

The Journal of Agricultural Science ◽

10.1017/s0021859600015963 ◽

1964 ◽

Vol 63 (3) ◽

pp. 297-303 ◽

Cited By ~ 7

Author(s):

J. R. Freney

Keyword(s):

Clay Minerals ◽

Organic Nitrogen ◽

Nitrogen Compounds ◽

Potassium Ions ◽

Salt Solutions ◽

Ammonium Fixation ◽

Naturally Occurring

1.Fixed ammonium could be completely recovered from clay minerals by leaching small amounts of clay with large volumes of salt solutions (containing the cations but not K+, Rb+, or Cs+), but no clay fixed ammonium could be found in soils when analysed by this technique.2. It is suggested that ammonium fixation is largely a laboratory phenomenon caused by the use of extractants containing potassium ions which trap exchangeable ammonium, or the use of reagents which decompose organic nitrogen compounds.

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