**Table2.**Resultsoffilmtensile test duringserviceperiodof0–180d.



 **3.** Variation of scale of decrease in film tensile properties with film-laying

#### 3.3.2. Results and Analysis of Test on Curl-Up Force in Film Collecting

The software Allpairs was used to generate a hybrid orthogonal table for the test [22], and the test results are shown in Table 4.


**Table 4.** Test plans and results.

According to the analysis of the results in Table 4, it can be obtained that under different test factors, the required film tensile stress for the operation of the curl-up film collector was 15.97–21.86 MPa. By comparing the value with the results of the film tensile property test, the minimum tensile yield stress of the high-performance film with a thickness of 0.01 mm was higher than the required minimum film tensile stress during normal operation of the curl-up film collector. The results of the range analysis showed that the influence order of the test factors on the film tensile stress was *Film Pick-up Angle* > *Sampling Position* > *Type of Film*; the film tensile stress achieved the maximum value when position 1 was chosen as the sampling position, the film pick-up angle was 30◦, and the film type was high-performance film.

In order to find out the significance level of the test factors on the test indexes, a variance analysis was made on the above test results, and the analysis results are shown in Table 5.



Note: \*\* means the effect is very significant.

According to the analysis results in Table 4, the required film tensile stress for the operation of the curl-up film collector under different test factors was 15.97~21.86 MPa. By comparing this range with the results of the film tensile property test, only the minimum tensile yield stress of the high-performance film with a thickness of 0.01 mm was higher than the minimum film tensile stress required in normal operation of the curl-up film collector. The range analysis results showed that the influence order of the test factors on the film tensile stress was Film Pick-up Angle > *Sampling Position* > *Type of Film*; the film tensile stress achieved the maximum value when position 1 was used as the sampling position, the film pick-up angle was 30◦, and the film type was high-performance film.

In order to verify the significance level of each test factor on the test indexes, a variance analysis was made on the above test results, and the analysis results are shown in Table 5.

It can be observed from Table 5 that the sampling position and film pick-up angle had significant influence on the film tensile stress, while the type of film had an insignificant influence on the film tensile stress. During the service period of the film, due to various reasons, such as the wind-blown sand, the soil on the film accumulates. Since the cotton plants can stop the sand, the soil accumulated around the center of each row along the film-laying direction decreases; the longer the service period of the film, the more obvious this tendency becomes. Therefore, when the sampling position was the front point of each row, the soil quantity on the film was highest; thus, the curl-up force required to pull up the film is very high. With the shift of the sampling position to the center of each row and, therefore, with less soil on the film, the curl-up force required to pull up the film reduces. According to Equation (7), the film tensile stress is directly proportional to the curl-up force; thus, the sampling position had a significant influence on the film tensile stress. The angle between the direction of the curl-up force and the ground is equal to the film pick-up angle. The larger the film pick-up angle, the larger the valid component force to pull up the film would become, and the smaller the curl-up force is required. Thus, the film pick-up angle had a significant influence on the film tensile stress. Although the type of film has influence on the soil's moisture content under the film, it has small influence on the cohesion of the soil under the film and the gravity of the soil on the film; thus, the type of film has an insignificant influence on the film tensile stress.

#### **4. Field Test on Curl-Up Collecting of Film**

By considering the test results of the contrast test on the tensile property under different test factors and the field test on film curl-up collecting between high-performance film and ordinary polyethylene film, the high-performance film with a thickness of 0.01 mm satisfied the requirements for the tensile stress of film in curl-up collecting. Since the value of the film pick-up angle is inversely proportional to the required curl-up force during curl-up collecting of the film, the film pick-up angle of the machine was set to 45◦–75◦ for film collecting. In order to verify the effect of the curl-up collecting of the film for film collectors with different structures on different types of film with different thicknesses, a test on field film curl-up collecting was designed, and the test site is shown in Figure 8.
