STUDIES ON THE STANDARD MATERIALS OF SOIL——THE COLLECTION, PREPARATION AND TEST OF HOMOGENEITY AND STABILITY OF SAMPLES Seasonal and interannual variability in soil respiration in wheat field of the Loess Plateau, China Sequence of a New HMW Glutenin Subunit Gene in Haynaldia villosa Homogeneity Index of Stand Spatial Structure of Mangrove Ecological System Prediction of minimum sampling mass of powders using drawing ball model Effects of Soil Nutrient Distribution on the Quantitative Characteristics of Community