Land-Use Conversion Altered Topsoil Properties and Stoichiometry in a Reclaimed Coastal Agroforestry System

Reclaimed coastal areas were mostly used for agricultural purposes in the past, while land-use conversion was initiated in recent decades in eastern China. Elucidation of the effects of land-use conversion on soil properties and stoichiometry is essential for addressing climate change and ecological conservation. In this study, five land-use types in a reclaimed area were chosen to compare the differences of soil properties and stoichiometry, which comprised paddy, upland, upland-forest, forest, and vegetable garden, with a soil age of about 100 years. The results indicated that these land-use types significantly differed in soil water concentration, pH, bulk density, soil salt concentration, soil organic carbon content, total nitrogen content, and total phosphorus, as well as C:N, C:P, and N:P ratios. Positive correlations were found among soil organic carbon, total nitrogen, and total phosphorus; and among pH, bulk density, and soil salt concentration. Total phosphorus and soil organic carbon contents were the main factors shaping the topsoil among the land-use types. Contents of soil organic carbon, total nitrogen, and total phosphorus in paddy and vegetable garden soils were higher than that in upland and upland-forest soils, while bulk density, pH, and soil salt concentration showed the opposite trends. Forest soil demonstrated intermediate values for most properties. And the highest C:N occurred in the upland and vegetable garden, the highest C:P in paddy and vegetable garden, while the lowest C:N and C:P occurred in upland-forest. The highest and lowest N:P occurred in paddy and upland, respectively. The stoichiometric characteristics presented a narrow range of the ratio, and the C:N:P averaged 48:3:1 similar to the stoichiometry of average Chinese cropland soils. Rotations including legume, the use of organic fertilizers, and appropriate fertilization strategies were suggested for improving cropland management.