پیش بینی ضرایب فعالیت برای راه حل داده های مخلوط آبی الکترولیت از راه حل های دودویی آنها

The simple equation relating the activity coefficient of each solute in mixed electrolyte solution to its value in binary solutions under isopiestic equilibrium was tested by comparison with the experimental data for the 18 electrolyte solutions consisting of 1:1, 1:2, and 1:3 electrolytes. The isopiestic measurements were made on the quaternary system BaCl2-NH4Br-NaI-H2O and its ternary subsystems NaI-NH4Br-H2O, NaI-BaCl2-H2O, and NH4Br-BaCl2-H2O at 298.15K. The results were used to test the applicability of the Zdanovskii's rule to the mixed electrolyte solutions which contain no common ions, and the agreement is excellent. The activity coefficients of the solutes in the above quaternary and ternary systems calculated from the above-mentioned simple equation are in good agreement with the Pitzer's equation.

Carbon and nitrogen cycles are very important to agricultural productivity and global climate stability. Human activities, for example, intensive farming and deforestation, also strongly affect these processes. On the Huang-Huai-Hai Plain of China the winter wheat-summer corn double cropping system has produced 99.77 million tons of grain, which has accounted for 80.0% and 27.5% of the total crop production in the region and the nation, respectively. Therefore, the sustainable utilization of agricultural soils in this area could affect China's food security. Since the early 1980s, some cropping practices have changed and caused soil organic matter (SOM) to rise in some sites (Kong et al., 2003), but fall in other sites (Wang et al., 1990) resulting in serious degradation of soil quality. On account of the complexity of SOM turnover processes and the dynamic response of SOM to environmental conditions, simulation modeling has become an important tool to explore and evaluate the dynamics of SOM in agricultural soils. To study SOM numerous carbon and nitrogen models, for example, ROTHC, CENTURY, DAISY, VVV, DNDC, and ECOSYS, have been developed during the past 30 years (Powlson et al., 1996). Mechanistic models, however, were often too complex, and it wasdifficult to obtain the required parameters or input data to run the models. For example, most of the above models needed iriformation on daily soil water and temperature dynamics, which in many cases was not available, especially on the field scale. Since the 1980s, researchers in China have been searching for simple but useful mechanistic models to simulate SOM dynamics (Wang et al., 1988; Yang and Janssen, 1997; 2000; Liu et al., 2001), however these models still lack thorough validation on SOM dynamics under field conditions. Douglas and Rickman (1992) first developed the D3R model to estimate the decomposition of cereal residues on the basis of cumulative degree-days calculated from daily mean air temperature. Curtin et al. (1998), under a greenhouse environment, used the D3R model to simulate the amount of wheat straw carbon remaining in the soil. Later, the D3R model was introduced into the CQESTR model to predict the effects of tillage and crop rotation on SOM decomposition and storage, using readily available input data at the field scale (Rickman et al., 2001, 2002). In this work, the CQESTR model was modified to evaluate the effects of intensive cropping on SOM dynamics at seven sites of the Huang-Huai-Hai Plain in North China and to estimate carbon dioxide emission from agricultural soils in this region.

Seven independent experimental validations of intensive agricultural soil showed that the modified CQESTR model may be an acceptably accurate and easy-to-use tool for predicting SOM trends at a single agricultural field on China's Huang-Huai-Hai plain. Through a further validation of field experiments, the modified model with calibrated parameters can be a powerful tool for estimating C storage potential and reconstructing C storage in intensive agricultural soils at a field level. The quantity and quality of SOhl were improved with the increment of annual crop yield and/or organic input. High SOM value and big SOM mineralization rate indicated high soil fertility. Statistical analysis suggested that the annual apparent soil respiration efflux reflected not merely the intensity of soil organism and plant metabolism but the annual SOM mineralization rate in the plow layer.