In order to reveal the effect of forage grass planting on improving saline alkali land and better develop and utilize the reserve land resources

the coastal saline alkali land in the Yellow River Delta was taken as the research object

using the methods of plot experiments

field sampling and indoor tests

we investigated the dynamic changes of physical

chemical and enzymatic activities of saline soils planted three annual forage grasses (Sorghum bicolor×sudanense

Sorghum bicolor 'Dochna’

Purus frumentum) during a growing period

and comprehensively evaluated the improvement effects based on the soil quality index. The results showed that: (1) Soil water content

pH and conductivity showed a decreasing trend with the increasing of growth time

and the most significant reduction in soil pH was observed for Sorghum bicolor×sudanense and P. frumentum during the vigorous growth period

and the best reduction in pH was observed at the harvest stage of Sorghum bicolor 'Dochna’. The soil conductivities of all three forage grasses were significantly lower than that of CK

and the reduction effect on 20—40 cm soil layer was better than that on 0—20 cm soil layer

among which P. frumentum was the best. (2) Planting of different forage grasses significantly improved soil nutrient content

and the content of soil organic matter

avail nitrogen and avail phosphorus increased significantly

but had little effect on soil avail potassium content. (3) The three forage grasses had different effects on soil enzyme activities at different growth periods. During the vigorous growth period

the soil enzyme activity was the strongest

and activities of soil catalase

sucrase and urease significantly enhanced. Sorghum bicolor 'Dochna’ had the greatest effect on activities of catalase and sucrase. (4) There were differences in the contribution of different forage grasses to the improvement index of saline alkali soil. Taking soil physical and chemical properties

nutrient content and soil enzyme activity as soil evaluation indexes

the soil quality after planting different forage grasses from high to low was Sorghum bicolor 'Dochna’＞Sorghum bicolor×sudanense＞P. frumentum＞CK. The research coud provide theoretical basis and important reference for the phytoremediation technology of saline alkali land in the Yellow River Delta and the screening and introduction of salt-tolerant plants with high ecological and economic benefits at home and abroad.