| A research on the period and depth of desulfurized gypsum being used in improving the alkalized soil is taken by applying desulfurized gypsum and planting oil sunflower on a piece of typical alkalized land in Xidatan of Ningxia.The experimental results show that applying desulfurized gypsum in different periods and depths has different effects on promoting the growth and yield of sunflower.If the desulfurized gypsum is applied in autumn other than in spring,the effect will be more distinct as the survival rate of sunflower seedlings can be improved by 21.2%～45.5%,and the yield can be increased by 16.2%～52.6%.If the desulfurized gypsum is deeply(25 cm) applied other than shallowly(10 cm) applied,the survival rate of sunflower seedlings and the yield can be respectively improved by 1.2%～5.4% and 1.2%～11.7%.When the desulfurized gypsum is applied in a different combination of period and depth,it will bring a different effect in improving the survival rate and yield.The effect on improving the growth of sunflower will be more distinct if the desulfurized gypsum is applied deeply in autumn,better than shallowly in autumn,deeply in spring or shallowly in spring.When it is applied deeply in autumn other than shallowly in autumn,deeply in spring or shallowly in spring,the survival rate of seedlings are respectively improved by 12.0%,25.6% and 21.5%,and the yield are respectively improved by 14.4%,32.7% and 29.9%.As the soil in Xidatan of Ningxia is deeply(25 cm) ploughed in autumn after harvest and is watered in winter,it is recommended that the desulfurized gypsum shall be applied deeply in autumn to improve alkalized soil. |