Effects of different Tamarix chinensis-grass patterns on the soil quality of coastal saline soil in the Yellow River Delta, China

Highlights: • Construction of circumlittoral shelter forest is of great significance. • The mixed forest-grass pattern TPA showed the greatest effects to reducing salt, and increasing the soil nutrients. • Grass species and the density of new Tamarix chinensis forest play a major role in soil-improving effects. Construction of circumlittoral shelter forest is of great significance to maintain ecological security of coastal zones, the safety of people's lives and property in the Yellow River Delta (YRD) in China. Tamarix chinensis-grass patterns have shown obvious advantages in construction of circumlittoral shelter forest and improving the soil quality of coastal saline soil. This study aimed to explore the soil-improving effects of various Tamarix chinensis–grass community patterns and identify the best vegetation pattern for improving the soil quality in the coastal saline-alkali land. Six kinds of Tamarix chinensis–grass community patterns were selected from the saline-alkali soil of the YRD, with bare land as the control. Effects of different Tamarix chinensis-grass patterns on the coastal saline soil were evaluated using statistical methods (e.g. principal component analysis and fuzzy membership function method). The results showed that various Tamarix chinensis-grass community patterns significantly decreased the salt contents and increased the available nutrient contents in the coastal saline-alkali soil. The soil improvement effects showed obvious distinctions among the different Tamarix chinensis-grass patterns. The mixed forest-grass pattern consisting of Tamarix chinensis, Phragmites australis, and other salt-resistant grasses showed the best effects in relation to reducing salt, preventing alkalization and increasing the soil nutrients, which resulted in the lowest salt contents and the highest nutrients. Grass species play a major role in increasing soil nutrient contents, and the density of new Tamarix chinensis forest contributes greatly to the decrease of soil salt. And the more kinds of grass species are, the better improvement effects they will have. Therefore, during the construction of the circumlittoral shelter forest system in the muddy coastal zone of the YRD, it is recommended to prioritize the high density Tamarix chinensis–Phragmites australis (TPA) community pattern, and live together with other kinds of salt-resistant grasses.