Island soil quality assessment and the relationship between soil quality and land-use type/topography

Information about the soil quality of different land-use types and topographies is essential for the sustainable development, utilization, and protection of soil resource in coastal areas. In this study, representative topsoil samples were collected from Liandao Island, China, and soil water content (SWC), soil bulk density (BD), total nitrogen (TN), soil organic matter (SOM), ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃^--N), available phosphorus (AP), available potassium (AK), soil salt content (SSC), and pH were recorded. The suitable minimum soil data set (MDS) was computed by principal component analysis (PCA) and the soil quality index (SQI) was then determined. The spatial distribution of the SQI was analyzed using ordinary kriging interpolation. The effects of topographical parameters (digital elevation model [DEM], slope, and aspect) and land-use types (vegetation [V], water resource conservancy land [WRC], sandy land [SL], unused land [UL], and built-up land [BL]) on SQI were then analyzed in detail. The parameters included in the MDS were TN, pH, and BD, which together accounted for 84.371% of the variation in soil quality. The SQI varied from 0.189 to 0.772 in the study area. The correlation coefficients between SQI and DEM, slope, and aspect were 0.498, 0.294, and 0.137, respectively (p < 0.01). The highest SQI score was found at an elevation of 110 m, with a slope of 68.2° and an aspect of 246.6, in the vegetation land-use type. Soil quality differed significantly (p = 0.0000) among the land-use types, with the following ranking: V > UL > SL > BL. Our results provide land managers with an important reference for the development, utilization, and protection of soil resource in coastal zones such as Liandao Island, China.