Abstract:In the use of first order kinetic equation to fit the kinetic data of ion adsorption, the crux is how to determine the value of N_∞ (the adsorbed quantity at equilibrium). Both erroneous N_∞ value and unsuited N_∞ value to the mathematical equation would lead to a wrong conclusion. In this work, based on a theoretical analysis of the first order kinetic equation of chemical adsorption mechanism and physical diffusion mechanism, a way to determine the value of N_∞ was advanced and verified by the ion diffusion and ion adsorption experiments.

Abstract:The distribution and formation of water-stable aggregates in red soils under different land use were studied. The results showed that the contents of >0.25 mm water-stable aggregates increased in the following order: orchard > tea garden > uncropped > upland > woodland. Either the waterstability of aggregates or the content of water-stable aggregates was highly correlated with the contents of soil organic matter. Increased decomposition and decreased input of organic matter after reclamation were responssible for the decrease in both the water-stability of aggregates and the amount of water-stable aggregates in red soils. Therefore, increasing organic matter input is crucial for improving the structure of red soils.

Abstract:X-ray photoelectron spectroscopy (XPS) technique was used to study the coordination forms and transformation characteristics of P on goethite surfaces at different pH. The results showed that the chemical forms of P on goethite surfaces changed from the dominance of monoradical ligands to that of biradical ones with increasing pH of the solutions. For a given P concentration, increasing the pH of suspension could cause a faster transformation of monoradical ligands of P to the biradical ones on goethite surfaces, while lowering the pH the biradical ligands converted slowly to the monoradical ones. By influencing types of phosphate ions in the solution, pH affected the coordination forms of P on goethite surfaces. The dissociation and association of protons of the sorbed P caused by pH changes were considered as a major reason leading to the transformation of the coordination forms of P on the surfaces. The stability of biradical ligands of P was greater than that of monoradical ones. and the possible reasons were disscussed in paper.

Abstract:Stability constant logK, which tested three kinds of soil soluble humic acids reacted with copper ion to form the complexes, appeared cultivated loessal soil>old manured loessal soil>yellow Ioessal soil. logK value was related to pH, temperature and ionic strength. The thermodynamic function variations in complexation were: △rGm^θ<0, △rHm^θ<0, and △rSm^θ<0, showing that the complexation reaction was a spontaneous exothermic reaction and that negative value of △rSm^θ<0 was in the same sequence with logK, wich was considered as the entropy effect of humic acid molecular deformation and complex stability in process of humic acid reaction with copper ion.

Abstract:Pot and incubation experiments were carried out to study the effect of alternate flooding and drying on the transformation and availability of phosphorus in calcareous soils. The results indicated that flooding significantly increased P availability in calcareous soil and enhanced the transformation of inorganic phosphate into more available fractions such a Ca₂-P and Fe-P. After draining and drying the process reversed in the soils.

Abstract:The urease activities and physico-chemical properties of nineteen samples collected from seven main soils in Shaanxi Province were analyzed. The results obtained by the correlation, path and principal component analyses showed that the soil urease activities varied significantly with the soil fertility level and soil physical and chemical properties had both direct and indirect influences on the urease activity. Similar evaluation results of soil fertility were got by using an information system of soil ertility consisting of principal component and by the urease activities and the physical and chemical properties respectively.

Abstract:In the work soil erodibility factor K of seven different types of soil in subtropical China was studied using field plots under natural rainfall condition. The field plots were established in Yingtan of Jiangxi Province. The results showed that there were great differences among soil erodibility factor K of seven different types of soils. Among them calcaric regosols developed on purple shale and cultivated cambisol on red sandstone had the highest factor K, being up to 0.440 and 0.438 (0.132 k.hr/MJ. mm) respectively. The lowest was eroded acrisols derived from Quaternary red clay, with factor K of only 0.104, being less than 1/4 of the factor K value of purple soil. The soil erodibility factor K of seven types of soils were also estimated by using the Wischmeier's nomography. These results showed that the factor K vaules of two types of soils estimated by the nomography were close to those measured using field plots, one of the seven types of soils had a bigger difference between the factor K obtained by the above two methods, three had a big difference, and one couldn't be estimated by the nomography. Therefore, the nomograph method for estimating soil erodibility factor K was almost unsuitable for the soil types in subtropical China.

Abstract:The main properties of litter and forest floor in Tianshan mountains were determined in a location test during 1992-1995. The results showed that the movement of nutrients in Tianshan forest ecosystem had its special circumstances: (1) Forest litterfall was lower (2.1 t/hm²) and its seasonal changes belonged to the single-peak type. (2) The sequence of nutrients returned in form of litter was Ca>N>K>P. Before falling, most of N, P, K was transfered, and the transfered amount of K was the greatest However, Ca was rich in litter, and it had the greatest amount of return. (3) The nutrient reserves and water storage capacity of forest floor were higher, but the rate of decomposition of organic matter was lower. (4) The sequence of leaching loss from forest floor was K>organic C>total N>total P.

Abstract:The biomass, growth, annual litter fall, main nutrient contents, and the influences on soil nutrients, soil microbes and soil biochemial activities of secondary forests in Xishuangbanna were studied. Results showed the characteristics of uptake, accumulation and return of biological materials and nutrients in secondary forests, and their effects on soil nutrients. Microbe decomposition of litter fall and biological nutrient cycling of secondary forests were also dealt with. The study provided a basis for further research of tropical forest ecosystem. The plants grew quickly in the tropical secondary forests. The uptake of nutrient elements was large and its proportion of return to uptake was about 0.5. A great quantity of nutrient elements was accumulated in plants with increasing age of trees, and soil nutrient content was low. With increasing age of secondary forests, uptake, accumulation and return of nutnent elements increased, the intensity of litter fall decomposition increased and the speed of material cycling was quick.

Abstract:A simulation study of the effects of some factors, such as row spacing, ridge height, wetting agent, compaction and the furrow orientation, on the evaporation and soil temperature from water-repellent soils was carried out with the model of heat and water movement in water-repellent soils. Water repellency is a problem for agricultural soils, but furrow cultivation could increase rainfall runoff and infiltration into the furrow, which would make the water-repellent problems tum into an advantage for germrnahon.

Abstract:Through theoretic calculation and field irrigation experiment, the deposition and dissolution of CaCO₃ and MgCO₃, of soil and the adsorption and desorption of ions in mineralized irrigation water-soil system were studied in this work. A calculating method of △G_CaCO3 and △G_MgCO3, for judging the deposition and dissolution equilibria of CaCO₃ and MgCO₃ was established according to the theory of electrolyte solution. The measured results in field experiment confirm to the theoretic calculating results of △G_CaCO3, and △G_MgCO3, of different icligation water. The solubility of CaCO₃ and MgCO₃ of soil was increased due to salt effect of mineralized irrigation water. The soluble calcium and magnesium contents of soil increased after the soil was irrigated with mineralized water. Planting reduces the K value of sodium adsorption Gapon equation and decreases the adsorption of sodium from irrigation water by soil in field condition.

Abstract:Molydenum content in beer barley was found in kernel>in leaves>m roots>in straw, and was significantly correlated to P-fertilization levels with an exception of stem (straw), while the magnitude of plant Fe content was in an order almost opposite to that of Mo. Root Fe increased with the increasing of P level, showing very significant correlation these two variables. Plant Fe obviously declined with too high P level (P₂O₅ 4.6g/pot). Root Fe was 8.61 times higher than that of leaf Fe, having the leaf P: Fe ratio hightened towards 63-75, causing chlorosis disorder. The highest Mo and Fe content in plant parts observed in this study appeared at P-level of 2.4g P₂O₅ per pot. Mo and Fe accumulated in matured plant was 14.9 and 3218 μg/pot, respectively. Distribution rate of Mo was 62.3% in kernel, but of Fe, was only 10.2%.Proper quantity of P-application was proved to be beneficial in crop yield and quality. There was evidence of the increment of 1000-seed weight, final yield, and seed starch content, also the decrease of crude protein.

Abstract:The effects of iron supply, nitrogen forms (N0₃^-N and NH₄⁺-N) and primary-leaves-shading on reutilization efficiency of Fe in bean plants and their mechanism were studied in nutrient solutions under controlled conditions. The 59 Fe isotopic method was also used to identify the iron reutilization efficiency. The results showed that Fe deficiency could enhance Fe translocation to young leaves from roots and primary-leaves, thus increasing Fe reutilization efficiency. The plants added with NH₄⁺-N had a much higher content of active Fe, more chlorophyll in young leaves and high Fe reutilization efficiency, much better ultrastructure chloroplast than those fed with N0₃^-N, and these were true both in Fe-sufficient and deficient treatments. No chlorosis occurred in young leaves of bean plants fed with NH₄⁺-N under Fe-deficient condition. More active Fe and 6 percent enhancement in Fe reutilization efficiency were found in the primary-leaves-shading treatment, which improved Fe nutrition in young leaves of Fe-deficient plants fed with N0₃^-N. All these results demonstrated that both NH₄⁺-N and primary-leaves-shading had a beneficial effect on mcreasing Fe reutilization efficiency, improving Fe nutrition in young leaves and depressing chlorosis symptom in bean plants.

Abstract:Two kinds of humic acids derived from different coal sources have been studied for three years. The results show that it is feasible to use humic acids as urease inhibitors. They could slowly reduce the decomposition of urea, lessen nitrogen pollution of environment, and significantly improve the activity of crop roots and the available utilization rate of soil nutrients. Also humic acids could be got easily and have little harmful effect on environment and organisms. While exploiting weathered coal resource,it could improve environmental conditions.

Abstract:A study was carried out to determine the effect of ammonium thiosulfate (ATS), a byproduct of petroleum refinery, on nitrification and to find its possible mechanism. These objectives were addressed by applying nitrogen fertilizer (urea) in combination with application of thiosulfate at different rates and simultaneously measuring changes in urea-N, NH₄⁺,N0₃^- and NO₂^- at various time in the course of incubation as well as thiosulfate transformation. The results indicated that ATS applied to the soil was rapidly hydrolyzed with an accumulation of tetrathionate and sulfate. Urea was completely hydrolyzed within 3 days with a rapid increase of ammonium content in the soil. The formation of nitrate from ammonium was markedly suppressed by the application of ATS. ATS is a promising nitrifieation inhibitor. At the highest rate of ATS (2500μg ATS/g soil) nitrification inhibition over 14 days was 82%. The inhibition of ATS in this study occurred in the initial period of nitrification and was caused by thiosulfate and its oxidation products such as tetrathionate.