| Summary: | 博士 === 國立中興大學 === 土壤學系 === 84 === Nitrogen is an important element of nutrition for crop
growing.Adsorption, fixation, and release of ammonium on the
soil are im-portant factors affecting the supplying ability of
soil nitrogen.Cropcan continually uptake and use the nitrogen
fixed by soilduring the growth. Simultaneously, the
nitrification of ammoniumdecrease indirectly because the
ammonium is fixed by soil, andreduce the extent of pollution in
the soil environment due to thereduce of large accumulation of
NO and NO. Therefore fromwhether the viewpoint of theory or
agricultural application, thathas an importantstudying
background for ammonium fixation ofsoils.Based on the difference
of layer charge derived from tetra-hedral or octahedral layer of
clay minerals, net negative surfacecharge, heterogeneous layer
charge of dioctahedral and trioctahedral clay minerals, and
exchangeable selectivity of ammonium, we studythe ammonium
fixation and mechanism of main soil groups of cultivatedland in
western Taiwan. A reduction in octahedral charge of swelling
clay minerals wasobserved after treatment with 3 M LiCl and
heating at 300℃ tocompare the difference between ammonium
fixation of tetrahedral andoctahedral layer charge. The
experimental results indicated thatamounts of ammonium fixation
of twelve soil clay representing Taiwan''s cultivated land were
reduced after treatment with 3 M LiCl andheating. The largest
percentage of reduction was 94.4％ for Erhlinseries; The
smallest percentage of reduction was 40.0％ for Chungtanseries.
This suggested that ammonium fixation is affected apparentlyby
octahedral layer charge of layer charge in twelve soil clay.The
octahedral layer charge of Taiwan''s soil clays was
neutralizedafter treatment with 3 M LiCl and heating at 300℃
that were inagreement with X-ray diffraction analysis.The
ammonium fixation on clay mineral surface was also affected by
cemented materialssuch as carbonates, organic matter, and free
iron oxides.To studythe relationships between ammonium fixation
and PZNC(Point of ZeroNet Charge), negative charge at PZNC, and
net nega-tive charge at pH 9 with adsorptive method of Na and Cl
withdifferent pH. The results showed that the range of PZNC of
allsoil clays was 3.3∼5.9, that decreased with increase of
montmori-llonite content and increased with increase of free
iron oxidescontent. The range of negative charge at PZNC was
-3.6∼-7.0 cmol/kg. When soil cemented materials existed, the
ammonium were fixedby tetrahedral layer charge(NH) decreased
with increaseof kaolins content. The range ofnet negative charge
at pH9 was-6.4∼-28.4 cmol/kg, thathad apparent relationships
with contentof kaolins and free aluminum oxides. NH apparently
decreasedwith increase of net negative charge at pH 9. It showed
that vari-able charge of kaolins and cemented materials
decreased ammoniumfixation of interlayer on effective fixed
sites. To study the effects of heterogeneous layer charge on
ammoniumfixation with FTIR(fourier transform infrared)
photometer to scansoil clay with fixed ammonium after treatment
of different temper-ature. The results indicated that decreasing
variation of band at3450 cm with the increase of temperature was
remarkable forKantsetou series, Wukueiliao(13) series, and
Shanhua series, theheterogeneity of layer charge was larger for
these soilclay, andfixed amounts of ammonium derived from
tetrahedral layer chargewere higher. Whereas, the decreasing
variation of band at3450cm with the increase of temperature was
not remarkable forErhlin series, that indicated the homogeneity
of layer charge onthe ammonium fixation, and amounts of fixed
ammonium derived fromtetrahedral layer charge were lower.The
FTIR spectra indicatedthat heterogeneityof layer charge was
larger, and the stabilityof fixed ammonium was lower; The
homogeneity of layer charge waslarger, and the stability of
fixed ammonium was higher.To study the relationships between
release of fixed ammoniumand heterogeneous layer charge with the
technique of voltammetry''sreductive current, and to identify
crystal character of mineralsin soil clay with thetechnique of
X-ray diffraction. Experimentalresults verified that release of
fixed ammonium agreed with thepotential of release was
determined byFTIR technique. It could beknown by amounts of
fixed ammonium derived from tetrahedral layercharge were higher
and decreasing variation of bandat 3450 cmwith the increase of
temperature was remarkable and the heteroge-neity of layer
charge was larger and released amounts of fixedammonium were
higher for Kantsetou series, Wukueiliao(13) series,and Shanhua
series. Released amounts of fixed ammonium did notincrease with
total amounts of fixed ammonium increased, and therelationships
was significant between released amounts of fixedammonium and
ammonium fixed by tetrahedral layer charge. Releasedamounts of
fixed ammonium in most experimental soil clay increasedwith the
ratio of ammonium fixedby tetrahedral layer charge/addedfixed
ammonium increased. Crytal character of main clay mineralsin all
experimental soil clay didn''t change due to the treatmentof
reductive current, and release of fixed ammonium really comefrom
release of interlayer''s ammonium in swelling clay minerals.
To study the relationships between exchangeable selectivityof
ammonium and ammonium fixation with Q/I diagram of
ammoniumobtained by adsorptive method of different concentration
of ammo-nium. The results indicated that Gapon exchangeable
selectivityconstant(KG) decreased with of montmorillonite''s
content in-creased for most experimental soils, and KG was
somewhat affectedby kaolins''s content. When whole content of
mica, vermiculite andkaolins were dominant, ratio of ammonium
activity and calciumactivity(AR) was lower. It indicated that
ammonium had mostopportunity to appear on edges of layer
silicates. Added fixedammonium increased with AR increased,
showed that amounts ofammonium on layer surface of layer
silicates were larger, andadded fixed ammonium were larger. When
AR was larger, amountsof ammonium on nonspecific adsorptive
sites(-NH) were larger.It also showed that ammonium on layer
surface of layer silicateswere larger,then amounts of ammonium
on nonspecific adsorptivesites were larger. KG was lower when
potassium existed. AR>AR showed that potassium adsorbed on
edgesdecreased ammonium ofedges and increased ammonium of layer
surface. -NH<-NHalso indicated that ammonium of nonspecific
adsorptive sites onsurface of soil clay increased when potassium
existed. The results were expected to be a basic background
of inorga-nic minerals for studying store and applying ability
of soil ni-trogen, ammonium dynamic in soil, and decrease of
ammonium nitri-fication to reduce the extent of pollution in
soil environment dueto accumulation of NO and NO.
Simultaneously, the results werealsoexpected to emphasize the
concept of proper applying nitrogenfertilizer with suitable
amounts to a suitable land in a suitabletime and attaining
perpetual soil fertility.
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