Spatial distribution pattern and influencing factors of soil salt in coastal saline-alkali land after afforestation with foreign soil

Abstract: Soil salinization has seriously restricted the ecological greening environment of saline-alkali land in the sustainable development of modern agriculture. This study aims to study the spatial distribution pattern and influencing factors of soil salinization in the coastal saline-alkali land after afforestation with foreign soil. The study area was taken as the coastal saline-alkali land in Xuwei New Area, Lianyungang City, Jiangsu Province, China. The field survey and soil sampling were then carried out. The soil electrical conductivity and pH value were also selected as the main indicators to evaluate the soil salinization. An analysis was made to determine the distribution pattern of soil salt in the 0-10 cm, >10-20 cm, >20-40 cm, >40-60 cm, and >60-100 cm layers of coastal saline-alkali land, combining with geostatistics, classical statistics, and Kriging interpolation. The spatial variation was explained using the semi-variance function optimization model, which fully and effectively reflected the soil saline-alkali information from the horizontal and vertical aspects. A comparison was finally made on the soil saline-alkali differences between the foreign and the original soil. The results showed that: 1) The soil electro conductivity of 0-10cm, >10-20cm, >20-40cm, >40-60 cm, and >60-100 cm soil layers varied with the medium intensity, particularly with the weakly variable pH value. The variation coefficient increased with the increase of the soil depth. A weak spatial correlation was found in the soil electro conductivity and pH values of most soil layers. The weak spatial variability was caused by random factors, where the autocorrelation caused the strong spatial variability. In addition, the salinity of the study area gradually deepened from the west to the east in the horizontal direction. By contrast, the soil conductivity value continuously increased with the increase of soil depth in the vertical direction. There was the highest correlation between the soil electro conductivity and the two adjacent soil layers. The correlation gradually decreased with the increase in depth. 2) The saline-alkali soil belonged to the extremely severe salinized soil, where only a few salt-tolerant crops can grow naturally and normally. There was an outstanding surface and bottom accumulation of salt in the foreign soil, indicating the salt return and alkalization. The measures of salt drainage and salt isolation can be checked regularly to slowly infiltrate into the soil by small water irrigation in the later maintenance. Plants with more salt-tolerant should be selected to plant on the land beside saline rivers and lakes. The foreign soil can also be improved for greening in the long run. 3) The influencing factors of the soil electro conductivity included the electro conductivity and pH value of rivers and lakes, soil pH value, altitude, vegetation, and climate. Therefore, more attention should be paid to formulate more suitable for the subsequent afforestation projects. There was also time variability in the soil salinity. Future research can be expected to focus on the temporal and spatial distribution of soil salinity, the physical and chemical characteristics of foreign soil in different years, and the influencing mechanism of the nature of rivers and lakes on the surrounding soil salinity. The finding can provide a strong reference for the development and utilization rate of heavy saline-alkali soil, in order to improve the construction of landscape and green space, particularly for the formulation of comprehensive improvement measures and management systems in the precise saline-alkali soil.