Characteristics of Salt-Affected Soil and Its Amelioration by Trees

Abstract

China is the most populated country in the world, but its cultivated land area is not large enough to fully provide for it. Farmland is gradually declining as a result of socioeconomic development and rapid urbanization. In order to meet the demand for grain production and alleviate the pressure on current arable land, wasteland must be reclaimed. Forestation is not only useful for saline–alkali soil utilization but can also improve soil properties and maintain ecological balance. Salt-affected soils are distributed widely across the earth; and, although there are various causes for the occurrence of salinization, generally it results from the accumulation of free salts to such an extent that degradation of vegetation and soils takes place. Furthermore, unwise human practices have also increased soil salinity by changing the natural balance of the water cycle in the landscape and allowing excess recharging of groundwater. This reduces suitability for plant growth and increases the potential for other forms of land degradation, such as soil erosion and structural decline. Thus, salinization is one of the most serious long-term threats to the sustainability of land and water resources in the world. Trees can tolerate a certain level of salinity, thanks to evolution and adaptation. Therefore, from the viewpoint of biological amelioration of salt-affected soil, planting trees is necessary and significant. After trees are established on saline lands, the water table may decline through increasing discharge and decreasing recharge. Additionally, the total salt content might decrease, especially surface soil layers and topsoil. The potential for the amelioration of soil physical and chemical states also exists.