Fixed ammonium in soils of Taihu Lake Region and its availability
1988
Wen Qixiao | Zhang Xiaohua | Du Lijuan (Academia Sinica, Nanjing (China). Nanjing Inst. of Soil Science)
The fixed ammonium content and the NH4+-fixing ability of paddy soils were determined and the availability on the fixed ammonium was studied. It was found that both the fixed NH4+ content and the NH4+-fixing ability of soils varied with the parent materials, they decreased in the order: Yangtze River alluviumloess-like materialquaternary red clay. About 18% of the total N in the soil layer of 0-20 cm and 34% of that in the soil layer of 0-100 cm were in the form of fixed NH4+-N. The availability of the "native" fixed ammonium was rather low, and varied considerably in different horizons, ranging from 0 to 13%, while that of the newly fixed NH4+ was very high, being nearly 100%. There was no evidence showing the effect of waterlogging on the availability of the fixed NH4+. The significance of NH4+-fixation in soil N fertility is discussed, and it is suggested that the values obtained by the submerged incubation method were not only lower than the real ones, but also incomparable due to the presence of NH4+-fixation and difference in NH4+-fixing ability among various soils.
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