Effects of Surface Charge of Taiwan Representative Soil Clays on Interlayering Ammonium Fixation

• Main Authors: Chen, Horng-Ji, 陳鴻基
• Other Authors: Juang Tzo-Chuan
• Format: Others
• Language: zh-TW
• Published: 1996
• Online Access: http://ndltd.ncl.edu.tw/handle/30623165637133891341

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.