Abstract:Twenty-four samples from three Holocene loess profiles on Loess Plateau were selected for zircon surface investigation. Under the scanning electron microscope, six classes of surface ultramicrotextures were identified. Semi-quantitative method was used to calculate the frequencies of occurrence of six classes of surface microstructures. Based on the characteristics of the surface features, the formation of the six-class features could be interpreted by chemical weathering, physical weathering and combinated weathering respectively. The types of zircon surface features and their occurrence frequencies could be used as an index to evaluate the extent and nature of weathering and the pedogenetic changes. Furthermore, pedogenic environments are discussed.

Abstract:Soil erodibility factor K of seven representative soil types in subtropical China was studied using field plots under rainfall simulator and natural rainfall respectively.The results showed that soil erodibility factor K of tilled Alfisol derived from red sandstone and Cambisol on purple shale was the highest, and of eroded Entisol derived from Quaternary red clay was the lowest. The relationships between soil erodibility factors measured by rainfall simulator and natural rainfall were also established respectively.

Abstract:This paper deals with the soils which were developed from weathering products of limestone in Anhui Province. According to Chinese Soil Taxonomic Classification (Revised Proposal), the paper discusses the places of 8 soil profiles in soil taxonomic classification. 2 soil profiles of them belonged to black Lithologic Isohumisols group, 1 soil profile to cab-Udic Luvisols group, and 5 soil profiles to cab-Udic Cambisols group.

Abstract:Based on the Udic Luvisols in the north subtropical region, this work studied the soil genus conception in the Chinese Soil Taxonomic Classifcation. mineralogical classes and soil temperature classes were selected Particle-size classes, as the criteria to identify soil genera. The nomenclature of soil genera was composed of the mainly characteristics combined with the subgroup name.

Abstract:The motive forces of ion diffusion in soils as a non-uniform electric-field system come from two aspects: concentration gradient and electric potential gradient So the Fick's diffusion laws is unsuitable for describing ion diffusion in soils directly. It is necessary to advance new fundamental equations for describing ion diffuiom in soils. Based on the fundamental theory of thermodynamics and dynamics of material diffusion, a set of fundamental equations descriding ion diffusion in soils has been obtained under the given conditions of experiment and through solving the fundamental equations, suecessful predication of ion diffusion in soils has been made.

Abstract:stationary experiment was conducted for 12 years at Hunan Agricultural University to investigate the effects of rice-based cropping system, organic manure groundwater level on phosphate sorption by paddy soils developed on red earth, in treatments of 3 types of rice-based cropping systems, 3 application rates of organic manure and 2 levels of groundwater table. Results showed that the phosphate adsorption isotherms for soils in all the treatments are quite similar in shape, belonging to curve in the shape of "L" with high affinity. The adsorption data all fit in well with the three adsorption equations at a very significant Langmuir equation is better than Freundlich and level of 1.0%, but the One-surface Temkin equations in this respect.

Abstract:In this work, an experimental study in heat and mass transfer in unsaturated soil was conducted. The influences of the different factors such as air temperature, air velocity and heat radiation on the migration processes of heat, moisture and salt were investigated. The dynamic distribution of temperature, moisture content and salt content in unsaturated soil under simulated climatic conditions was obtained. It is found that unsaturated soil can be divided into three regions as absorbing, transiting and releasing in moisture migrating process. The positions of different regions, the depth of heat infiltration and the equilibrium time for heat and mass transfer processes were determined. The results could be used to examine and correct the theoretical models of heat and mass transfer in soil.

Abstract:On the basis of temperature influences on diffusion transmission factor(f) through influencing water viscosity (η), it was advanced that viscosity correction coefficient (κ) could be described by the equation κ=η₂₅/η_o where η₂₅ and η_x, stand for the water viscosity at 25℃ and x℃,respectively, and the modified Nye model to estimate the diffusion coefficient of phosphate in soil under varying temperature was in the form of D=D₀κfθ/b. By using the adsorption isotherm slope (b) under a lower ratio of solution to soil and lower concentration of phosphate solution, the diffusion coefficient predicted by the model was in agreement with the diffusion coefficient measured, especially at indoor temperature. The ratio of the predicted phosphate diffusion coefficient to the measured phosphate diffusion coefficient in soil under low water tension condition(<105 Pa) was lower than 2 in most cases.

Abstract:The growth of wheat and sugar beet under salt stress and their uptake of salt were studied through greenhouse and field experiments. The salt tolerance of wheat was lower than that of sugar beet. Na⁺ inhibited the uptake of K⁺ and Ca²⁺.The relations between relative dry weight of wheat and sugar beet and soil salt content confirmed to the Maas-Hoffman model. Na⁺ contents in leaves of wheat and sugar beet had positive linear relations with the salt content of soil. Their relations with the relative dry weight of the crops also confirmed to the Mans-Hoffman model. According to these results, on the basis of Maas-Hoffman model between the Na⁺ content in leaves and the relative dry weight of crop, a method for the dynamic monitoring, diagnosis and prediction of salt injuries to crops was proposed. The predicted results about salt injuries to wheat and sugar beet in fields are satisfactory by this method.

Abstract:The effect of irrigation water quality on unsaturated hydraulic conductivity (k) of undisturbed soil and its mechanism were studied. Results showed that the higher the mineralization degree of irrigation water, the higher the soil hydraulic conductivity became. High sodium-adsorption ratio (SAR) of irrigation water would have an unfavorable effect on soil hydraulic conductivity. The irrigation water with a very low mineralization degree had an irreversible effect on soil hydraulic conductivity, inducing a significant decrease of soil hydraulic conductivity. The effect of irrigation water quality on physical properties of the experimental soil was also studied.

Abstract:A long-term stationary experiment was designed to determine crop responses to several major fertilizers in fluvo-aquic soils and the effect of fertilization models on soil nutrient supply. Results showed that fluvo-aquic soil had a great production potential. But on infertile fluvo-aquic soil, crop response to single N or P fertilizer was very limited. When they were applied in combination, the effect of their interaction on crop yield became significant. Once fertilization stopped, crop yield dropped down drastically to a very low level. On K-rich fluvo-aquic soil, the practice of no application of K and organic manure for 5 years did not cause any threat to crop yield. However, the readily available K in the plowed layer decreased at a rate of 3.8 mg/kg per annum, approaching the critical level. The long-term experiment also showed that the cumulative recovery rates of N and P fertilizers in the 5 years, 57.2% and 43.8% repectively, were much higher than the results in a single cropping experiment. With the current fertilization models and crop yield level, little surpluses of N and P nutrients and organic metter exited in most fluvo-aquic soils, whereas K deficit occurred in almost all the fluvo-aquic soils.

Abstract:Methods for screening winter wheat genotypes tolerant to low potassium level were studied by water culture and field experiments on a soil of low potassium fertility. It was observed that the amount of K absorbed was better than potassium utilization index when used as the screening index. The 1.0 mmol/L K concentration of the medium was found to be the suitable index at jointing stage of the plant. There was a significantly positive correlation between grain yield and the K content of shoot for 7 genotypes of winter wheat on the low-potassium soil (r=0.945^**,n=21). The amount of K absorbed by winter wheat was most from the non-exchangeable K of the soil that can not be extracted with lmol/L hot HNO₃ was the largest. The amount of K absorbed by winter wheat could also be used as a field screening index.

Abstract:No-tillage is one of the most important agricultural management systems. One way to determine if an ecological system can be sustainable is to evaluate the long-term effects it has on soil properties and on crop yields. The study was conducted from a 25 years'continuous no-tillage (NT) and conventional tillage (CT) corn (Zea mays, L.) production experiment on a Maury silt loam (Typic Paleudalfs) soil. The results showed that there was no significant difference in soil bulk density between CT and NT. Soil pH decreased and soil organic C and N increased with increasing application of NH₄NO₃ fertilizer. Soil organic C, organic N, exchangeable Ca, Mg,K and Mehlich Ⅲ P in 0-5 cm soil layer were all significantly higher with NT than with CT. During 25 years, the yield of NT corn had no significant difference from that of CT corn. For the last 11 years (1984-1994), the yield of NI corn was significantly higher than that of CT corn. This means that the continuous corn production with long-term mulched no-tillage treatment is a sustainable production system on this Typic Paleualfs.

Abstract:An optimization model for yield and fertilizer efficiency was established by many years and sites experimentation of N and P fertilizer combination for maize production in black soil region. The results showed that the optimum rate of N applied was 172.9kg/ha, that of P₂O₅ was 57.4kg/ha, and the optimum N:P₂O₅ ratio was 3:1, which could win an optimum yield of 7791.0 kg/ha. Within the range of optimum rate of fertilizer application 14.4kg and 16.9kg of maize yields could be increased by each kg of N and P separately when the applied amounts of N and P were equal. The efficiency of phosphorus fertilizer was better than that of nitrogen fertilizer, but the yield-increasing potential of N was far higher than that of P.734.9kg/ha of maize yield could be increased if only phosphorus fertilizer was applied, but 1597.9kg/ha of the yield could be increased when only nitrogen fertilizer was applied. Under the condition of optimum fertilizer application, N fertilizer's efficiency was 23.8-37.1%,and P fertilizer's efficiency was 14.2-22.2%. 68.9% of maize yield was dependent upon the soil.

Abstract:In this work, the speciation distribution and availability of selenium in different soils of Shanghai were studied. The results showed that selenium speciation was closely related to the pH and the contents of organic matter in soils, it existed mainly in the elemental, organic and sulfide hound forms, which accounted for 43-60% of the total selenium, secondly in the residue form, which accounted for 23-43%, and the amount of the other forms accounted for only 12-21%.Statistical analysis proved that the soluble, exchangable and carbonate bound forms of selenium were the most available for plants. This suggested that the methods to extrac available selenium by NaHCO₃ or KH₂PO₄ could be used to evaluate the availability of Se in soils.

Abstract:Soil samples from a long-term spot experiment (17 years) with different treatments were used for studying the oxidation stability of soil organic matter and humic acid fractions by the alcohol precipitation technique, and the optical properties of humic acid and its fractions. Types of humic acid and its fractions were also classified. With applying organic materials (compost or corn straw) for a long time, soil organic matter content increased obviously, its oxidation stabilily decreased; the distribution center of soil humic acid fractions moved to the fraction precipitated by alcohol with a high concentration, and the proportion of fractions with a smaller partical size rose; E₄ and E₆ values of humic acid decreased and E₄/E₆ increased. Application of chemical fertilizer resulted in a contrary result.

Abstract:The immobilization of fertilizer N by soil microbes and its changes in brown soils of different fertilization treatments were studied by a 14-year field location experiment using the ¹⁵N isotope tracer technique. The results of pot experiment showed that the immobilization of fertilizer N by microbes in various treatments reached a maximum after 5 days of fertilization, making up 13.3%-15.4% of the nitrogen applied except single application of nitrogen. In single N treatment the immobilization of fertilizer N by microbes accounted for 5.4% of the nitrogen applied. The increase in microbial biomass N after fertilization originated mainly from fertilizer N. Fertilizer N in the biomass accounted for 64.1%-87.3% of the total microbial biomass N. The biomass N was gradually released during crop growth. At the tillering stage of wheat the immobilization of fertilizer N by microbes decreased markedly, making up only 1.72%-3.29% of nitrogen applied. After the tillering stage the biomass ¹⁵N tended towards stable. ¹⁵N released by biomass accounted for 34.3%-54.3% of ¹⁵N absorbed by crop in different fertilization treatments except the application of alone fertilizer N. There existed a close relationship between the ¹⁵N released by biomass and the ¹⁵N absorbed by wheat(r=0.860).

Abstract:磷的测定研究,取得了很多新进展,日前采用的都是一些经典的测磷方法,这些方法因用化学试剂提取土壤中的有效磷而受到了诸如pH等土壤性质的影响,而使测定值偏高或偏低^[1]。Val。DerZee等1987年提出一种滤纸测磷方法^[2],近似根系在土壤中对有效磷的吸收,但为室内实验研究。作者把滤纸作为一种吸附介体直接用于森林土壤有效磷的测定,省去了土样采集和处理等步骤,简单易行,能较真实地反映土壤中游离的供植物根系吸收的有效磷含量。

Abstract:土壤微量元素的空间分布特征是土壤母质成分和外源输人长期作用的结果,了解这一分布特征是进行土壤环境评价的重要前提。地统计学中的条件模拟方法由于同时考虑了分布在二维或三维空间的变量整体上的空间结构特点和局部的不确定性,因而在研究变量的空间分布、变化和相互联系等方面具有独到之处,并在有关领域得到了广泛的应用。本文根据地统计学原理,对北京东郊污灌土壤表层微量元素含量的小尺度分异进行了条件模拟,为考察该方法的特点,同时进行了克里格括值以作对比分析。