Abstract:Acid sulfate paddy soil is one of the problem soils in Guangdnng province. This study deals with the general properties of sulfur chemistry of acid sulfate paddy soils in Guangdong province. The minerals of lightly yellow mottles in acid sulfate paddy soils were analysed and identified with X-ray diffraction, and the total S, water soluble S, exchangable S, pyrite, jarosite, organic S, etc. were estimated. The data obtained showed that the S in acid sulfate soils was mostly in inorganic forms and dominated by pyrite (FeS₂). The.soils was getting acid mainly due to the oxidation of pyrite in the process of reclamation and drainage of man-grove swamp. With the planting rice by periodical irrigation-drainage, the oxidation of pyrite.and formation and hydrolysis of jarosite in the soil were promoted, resulting the decrease of pyrite and the jarosite going downwards gradually in the profile, all these facts indicate that the form, distribution and amount of S compounds, espeically pyrite and jarosite, in soil are,closely related with the developmant of the acid sulfate soils. Therefore, it is suggested that the chemical properties of S in the soil could be used as an indicator in identification and classification of acid sulfate soils.

Abstract:For study of factors affecting soil. salinization, modelling experiment by soil columns was conducted in laboratory. The factors invertigated included salinity of ground water, organic matter content in plow layer of soils and patterns of solum structure.. The experiment results showed that (1) there was a positive correlation between salinity of ground-water and salinization of soil; (2) soil organic matter could inhibit the salinization of soil, theeffect of soil organic matter on soil salinization was observed when the soil organic matter content was above 1.5%; (3) the effect of intercalated layer of clay in soil profile on the inhibition of soil salinization depended upon the depth of the clay layer and its position in profile, the effect was getting significant with the increase of its depth and rising of its position.

Abstract:A simulation study of the infiltration rate was conducted for four soils with different rain patterns. Computational results showed that the rain water was infiltrated into soil when the infiltration rarer was greater than the rain rate at the earlier stage of the rain, and then the infiltration flow was calculated by analogy with saturated piston-flow, the infiltration rate was in direct proportion to the suction head at the wetting front, a front of demarcation between saturated and unsaturated zones, and in inverse proportion to the saturated zone length. With the,definition of nondimensional suction head equal to the suction head divided by its maximum one, the nondimensional heads calculated from the theory of Mein and Laison and predicred by the sitnelation study were in goad agreement.By using the piston-flow concept,the method to determine the ponding time and wetting front depth has been derived in this study. Also, the analytical solution for infiltration rate and wetting front location below the soil surface, during the period when rain intensity is alwayes greater than infiltration, has been obtained.

Abstract:Based on the law of mass conservation and the transient profile method used in determining the unsaturated hydraulic conductivity of soil, the method for determining the unsaturated dispersion coefficient of soil was developed. It was shown by field experiments that the method was effective in estinnating unsaturated dispersion coefficient under field condition, even for heterogeneous soils or those of spatial variability in their properties. The method has two advantages, i.e. simplicity in experimentation and computation and values of D and V and their relationship for a group of plots being able to be obtained from an experiment. Modelling experiments have shown this method is, reliable.

Abstract:Studies on the properties of water vapor adsorbed on some loessal soils were conducted by means of the method of equilibrium water vapor pressure, and the thermodynamic functions (relative partial molar enthalpy, entropy and free energy) were derived by using adsorption isotherm.

Abstract:The thermal status and nature of the main types of soils in China were studied by differential thermal analysis (DTA) method. The results obtained showed that all the samples had lower exothermic peak at about 300℃; only black soil and yellow brown earth had both of lower and hi gher exothermic peaks.

Abstract:Surface samples of five Ultisols (Dothan Red Bay, and Orangeburg from Florida, Manana from Hawaii, and Huangjinni from Zhejiang, China) and one Oxisols (Wahiawa from Hawaii) were used to ascertain the effects lime and organic matter on P adsorption and desorption under flooded condition. Reagent-grade calcium carbonate and ground dry clover tissues were used as lime and organic matter sources. Both lime and clover tissue addition increased soil pH and decreased Eh, but their effects on pH and Eh of the three Florida soils were less than that on other three soils. Flooding reduced the amounts of Al extracted by 0.5 M CuCl₂. Lime and clover treatments further reduced it for the three Florida Ultisols, but the reverse was true for the other three soils. The amendments reduced the P adsorption for the three Florida soils and the order of reduction followed: clover tissues < lime < mixture of clover and lime. The effect was reverse for the other three soils. For the three Florida soils, additions of lime and clover tissues increased the P desorption; for the other three soils, the opposite was true. Phosphorus adsorbed by the flooded soils was significantly related with oxalate-extractbale Fe, Al, and Mn and CuCl₂-extractbale Al, which suggests that the components controled P retention by flooded soils include not only pooly crystalline and amorphous Fe oxides and hydroxides, but also Al-OH polymer and Al bound with organic matter.

Abstract:Present paper deals with the characteristics of phosphate desorption isotherms of soils and clay mineral and P desorption with various extraction solutions. Isothrrmal adsorption of samples was first made and then phosphated sample were continuously desorbed by mean of the extraction with 0.5 N HOAc, 0.5 N NH₄F and 0.1 N NaOH or with 0.5 N NH₄F only.

Abstract:Surface charge characteristics of the clay fraction of a laterite derived from basalt and a red earth derived from Quaternary red clay in southern China were investigated based nn a model for describing charge characteristics of soil systems containing both permanent and variable charage minerals. pH₀, ZPNC and IEP were used as indexes to characterize surface charge Properties. The pH₀, denoting zero point of charge of variable charge system, was determined with potentiometric titration method. ZPNC, which means zero point of net charge of mixed systems with variable and permanent charge, was treasured with ion adsorption method. IEP was determined by electrophoresis method. The pH₀ value, ZPNC,and lEP of the laterite were higher than that of the red earth due to differences in clay mineral composition and in content of oxides of iron and aluminum between these twa soils. Because the quantity of perrnarxent negative charge of the red earth was comparatively high, the difference between pHo and ZPNC for this soil was more remarkable. After the addition of 3% organic matter and incubation for four moxiths under submergic corAditxons, the humus content of the clay fraction of these soils increased by less than 0.5%, its effect on the pH₀ value was indistinct.

Abstract:Ammonium adsorption and desorption were investigated with colloid samples of black soil,manured loessial soil, yellow brown earth, red earth and latosol as well as clay minerals. Adsorption of ammonium by soil colloids and clay minerals fitted to the two surface Langmuir adsorption equation. Binding strength was in the order: yellow brown earth > black soil,manured loessial soil>red earth>latosol, but the ammonium desorption ratio showed the opposite sequence. Langmuir parameter (K₁) was directly proportional to the relative affinity of soil colloids for ammonium (A). Langmuir equation constant (M₁+M₂) was positively correlated with CEC of samples, while the difference between K₁ before and after removing organic matter (ΔK₁) was negatively correlated with ΔOM.Removing organic matter could increase the affinity of soil colloids for ammonium and tended to decrease the ammonium desorption ratio.Annnonium adsorption behavior was determinedby the composition and surface properties of soil colloids, it was also influenced by clay-humus intereaction. Adsorption sites with permanent negarive charge showed stronger selectivity for ammonium than those sites with variable charge.

Abstract:The loss of nitrogen in the medium treated with amorphous ferric oxide was investigated with ¹⁵N-labelled ammonium sulfate in the incubation flasks under anaerobic condition. The gaseous composition of the atmosphere air in the upperspace above the same medium solution in the serum bustle was analyzed by Organic Mass Spectrometer during the experiment period. It was found that various gaseous fractions of ¹⁵N and nitrogen Loss occurred in the medium contaming ¹⁵NH₄-N due to applying amorphous ferric oxide under anaerobic condition. The gaseous Fractions emited from the medium involved ¹⁵NO₂, ¹⁵N₂O, ¹⁵N¹⁴NO, ¹⁵NO, ¹⁵N₂ and ¹⁵N¹⁴N. The rate of ¹⁵N lass was about 15%.It was primarily proved that the amorphous ferric oxide may act as an electron acceptor in the oxidation of NH₄⁺-N under anaerobic condition. It rnay be another mechanism for nicrogen loss in paddy soils.

Abstract:Results of simulation, pot and field experiments with brown earth showed that (1) the inhibition rate of soil urease activity by hydroquinone increased with increasing application rate of the latter, and the duration necessary for the restdration of urease activity decreased with decreasing application rate of this organic compound; (2) applying proper amount of hydro-quinone increased the utilization rate of urea-N by springwheat and decreased the gaseous loss of urea-N; (3) applying proper amount of hydroquinone, and urea before sowing without ropdressing of urea in growing period markedly increased the yield of maize; and (4) in treatments of applying hydroquinone, no accumulation of this compound was found in soils, stems and grains.

Abstract:稻田在淹水期间,水层的氧化还原电位明显高于土壤耕层,二者的电位差一般为0.2—0.6伏。于天仁等研究过水稻土淹水期间氧化还原电位在剖面上的分布^[1]。

Abstract:国内外大部分《土壤学》教材中,有关l:1型、2:1型结晶粘土矿物的结构图示^[2,6-8]都沿用了“Hofmann结构”图示^[1],用以说明结晶铝硅酸盐矿物Si—O、Al—O之间的结构关系。