The temperature difference between the ground temperature of the black mulch is small, the permeability of the black mulch is better than that of the white mulch, the plants of the black mulch are not prone to premature aging, and the nighttime temperature of the black mulch is high. Plastic film features: ground cover film, usually transparent or black PE film, also green, silver film, used for ground cover, to increase soil temperature, maintain soil moisture, maintain soil structure, prevent pests from attacking crops and caused by certain microorganisms diseases and other functions that promote plant growth.
Black plastic film features:
Black plastic film transmittance is only 1-3%, only 30-40% heat radiation. Since it is almost non-transparent, weeds cannot germinate and perform photosynthesis, so the weeding effect is significant. Black mulch in the sun, its rapid warming, high humidity, but the heat transferred to the soil is less, so the warming effect is not as good as transparent film, there is cooling effect in summer. When used, tile it on the ground so that the crop can be exposed outside the membrane and it can also be spread between the rows of crops.
In vegetable cultivation, vegetable growers usually use a very thin (0.015 to 0.02 mm thick) polyethylene or polyvinyl chloride black plastic film to cover the surface.
Black plastic film function:
1. Increase the geothermal temperature. The use of transparent black plastic film cover, generally can increase 3～6℃ of 5 cm deep topsoil temperature, increase the temperature is conducive to rapid seedlings in early spring after planting and promote root growth. The black plastic film covered in the spring greenhouse has obvious effect on the temperature increase. According to the determination, in the spring greenhouse, the average soil temperature of the 5-20 cm deep soil layer in the black plastic film is 0.5-2°C higher than that of the greenhouse alone. Autumn black plastic film coverage also has a good warming effect.
2. Drought prevention, flood prevention, anti-return salt. On the surface of the mulch covered with black plastic film, rainwater is discharged along the membrane into the sulcus and the soil moisture is generally not excessively saturated. When it is not raining, the water in the lower layer of the soil can run vertically from bottom to top, and the water in the gingival ditches can also be transferred laterally along the gingival rim to the middle of the pods, and the plants can absorb them. During drought, the membranes impede the evaporation of soil moisture and have a water retention effect, which can reduce irrigation times. Saline-alkali land covered with black plastic film can reduce surface salt re-salt. According to the determination, the total salt content in soil layers of 0 – 5 cm and 5 – 10 cm can be reduced by 41.31% and 2.24%, respectively.
3. Anti-soil compaction. During the growing season, the black plastic film covers the surface of the soil to reduce the wind and rain and people in the management of trampling, can make the soil to maintain a good loose state, prevent soil compaction.
4. Prevention of nutrient loss. After the black plastic film is covered, the soil temperature and humidity are suitable, and the permeability is good. The maximum temperature of the soil can reach above 30°C. Therefore, the soil microorganisms increase and the activity is enhanced, which can accelerate the decomposition and transformation of organic matter and promote the activity and reproduction of soil beneficial microorganisms. The effective nutrients in the soil increase, generally saving about 1/3 of the fertilizer. Due to the barrier of black plastic film, nitrogen in the soil can be prevented from evaporating, and leaching loss caused by rain erosion can be prevented.
Advantages and disadvantages:
First, keep fertilizers strong. In the soil covered with black mulch, the soil organic matter is in a normal circulation state due to a steady change in soil temperature. The measurements show that the total nitrogen, organic matter, available potassium, and alkali-hydrolyzed nitrogen in the soil under the black-film-covered crops are better than There are various degrees of improvement in the coverage of transparent films.
Second, good water retention. According to the test, the water content of 5 cm below the ground after the black plastic film is covered is 4-10% higher than that of the transparent film no matter whether it is two days after the cover or 35 days after the cover.
Third, prevent adverse effects. Black mulch film has low light transmittance and low radiant heat transmission, so it can make the soil temperature of the covered soil change little. According to the test, the soil covered with black film, in the period of plant growth, the soil temperature is 1-3 °C lower than the transparent film. As the warming rate is small, it is conducive to the normal growth of crop roots, especially those vegetables that are less demanding on the soil temperature, such as tomatoes, beans, and bell peppers.
Fourth, increase food production. Since the black plastic film has less soil temperature than the transparent film, especially some root systems require low soil temperature crops such as tomatoes, green beans, kidney beans, and late-maturing watermelons, etc. The height of the membrane. According to the experiment, the effect of increasing yield during the cultivation of tomatoes covered with black film is the most obvious, with an increase of 11.8%.
Fifth, suppress weeds. Grass cover is a serious problem when covered with transparent membranes. After being covered with agricultural black mulch, ground weeds are difficult to grow due to insufficient light conditions. Measurements show that after covering the dark film with a light transmittance of 5%, soil is almost a month later. Weeds are not seen. When covered with a black plastic film with a light transmittance of 10%, weeds grow in the soil, but the growth power is weak and does not cause disasters.
Disadvantages: Warming is not as fast as white plastic film.