Characteristics and influence of topsoil porosity in the northern agro-pastoral ecotone

In the present study, Zhangjiakou city was selected as the study area, and the characteristics of soil porosity in the northern agro-pastoral ecotone, and the factors influenced by these characteristics, were analyzed. The results demonstrate that the topsoil porosity in the study area is suitable for plant growth due to critical maximum porosity values and the ratios between capillary and non-capillary porosity. The maximum porosity of the topsoil was around 42.6%, the capillary porosity was around 24.6%, and the non-capillary porosity is about 18.0%. The ratio between capillary and non-capillary porosity was around 57∶43. The maximum porosity of the topsoil was significantly different between the Bashang Plateau and Baxia areas (P < 0.05), with values of 39.98% and 44.69%, respectively. However, there were no significant differences in maximum porosity, capillary porosity, or non-capillary porosity between land use types or soil types (P < 0.05), implying that the spatial distribution of topsoil porosity in Zhangjiakou city was mostly affected by landform factors. At the whole study area scale, topsoil porosity was correlated with soil quality parameters such as soil bulk density, soil organic carbon, soil water capacity, and sand, silt, and clay contents (P < 0.05). However, considering the influential factors in different areas, topsoil porosity was mostly correlated with soil quality parameters in the Bashang Plateau (P < 0.05), but was not correlated with soil quality parameters in single region of land use types or soil types. In general, the topsoil porosity mostly affected soil water capacity in Zhangjiakou City, and had a weak influence on other soil quality parameters.