**2.4 Field application of algae crust**

Field inoculation: the collected algal solution was evenly injected into the sandy land surface with a sprayer, and the amount of algal solution was 3 g dry weight m−2. For the first 10 days after inoculation, spray water every 2 days (the surface is moist), stop watering during rain. A month later, to measure the formation of algae crust, the topsoil area of 5 cm<sup>2</sup> and the thickness of about 5 mm were used for detection (due to the main algae distributed within 5 mm of the soil surface, so each sampling should be no more than 5 mm), and the content of chlorophyll a and chlorophyll b were measured.
