1.
Raise the ground temperature. Covering with transparent black plastic film can generally increase the surface soil temperature by 3 ~ 6℃ at a depth of 5 cm. Increasing the ground temperature is beneficial to quickly slow down seedlings after sowing in early spring and promote the growth of vegetable roots. The effect of black plastic film mulching in greenhouse in spring is very obvious. According to the measurement, the daily average ground temperature of the 5 ~ 20 cm deep soil layer covered with black plastic film in greenhouse in spring is 0.5 ~ 2℃ higher than that of a single greenhouse. Black plastic film mulching in autumn also has a good warm-keeping effect.
2.
Prevent drought, waterlogging and salt return. On the border covered with black plastic film, rainwater flows into the border ditch along the film and is discharged, so the soil moisture is generally not supersaturated. When there is no rain, the water in the lower soil can move vertically from bottom to top, and the water in the border can also be transferred laterally to the middle of the border for plants to absorb. In dry weather, plastic film hinders soil water evaporation, has water conservation function, and can reduce irrigation times. Covering saline-alkali land with black plastic film can reduce the salt return of surface soil. According to the determination, the total salt content in 0 ~ 5 cm and 5 ~ 10 cm soil layers can be reduced by 4 1.3 1% and 2.24% respectively.
3.
Prevent soil from hardening. In the growing period of crops, black plastic film mulching can reduce the trampling on the soil surface by wind, rain and man-made, keep the soil loose and prevent the soil from hardening.
4.
Prevent nutrient loss. After being covered with black plastic film, the soil has proper temperature and humidity and good air permeability, and the highest temperature of the soil can reach above 30℃. Therefore, the increase of soil microorganisms and the enhancement of their activities can accelerate the decomposition and transformation of organic matter and promote the activities and reproduction of beneficial microorganisms in the soil. The increase of available nutrients in soil can generally save about 1/3 of fertilizer consumption. Due to the barrier of black plastic film, it can prevent the volatilization of nitrogen in soil, prevent leaching loss caused by rain erosion, and play a role in maintaining fertilizer.