*3.1. Test Conditions*

The field test was carried out at the field research and development base of the Northwest Oasis Agricultural Environment Key Laboratory of the Ministry of Agriculture, Tuobuliqi Town, Korla City, Bayingolin Mongolian Autonomous Prefecture, Xinjiang Uygur Autonomous Region in early November 2021. The planting mode (660 mm (wide row) + 100 mm (narrow row)) with protective rows on both sides was adopted, and the film thicknesses were 0.008 mm and 0.01 mm for both the high-performance film and ordinary polyethylene film. The ground was relatively flat, and the drip irrigation belt had been recycled. Using the TZS-1 soil moisture tester, the moisture content of the surface soil was

16.2%. Before the test, the height of the stubbles in the test field was controlled within 120 mm. The test field is shown in Figure 6.

**Figure 6.** Test field on curl-up force in film collecting: 1—HP-50 type Digital Display Pull and Push Strength Calculator, 2—film.

#### *3.2. Test Method and Design*

#### 3.2.1. Test Factors and Levels

It can be known based on Equation (6) that the value of the curl-up force *F* is related to cohesion between the soil under the film and the film *Fa*, the film pick-up angle, the gravity of the soil on the film at the slope in the film pick-up *G*2, and the friction *f* <sup>2</sup> between the film and the soil on the film. Since the moisture content of the soil under the film of different types is different, the higher the moisture content under the film, the higher the cohesion Fa of the soil under the film to the film. The mass of soil on the film is related to the film-laying position. Since cotton plants can shield sandstorms, with the passage of time, the mass of soil near the middle part of the field is lower, and the friction of the film to the soil on the film at the slope is related to the friction coefficient between the soil friction and soil, as well as the mass of soil on the film. Therefore, the sampling position, film pick-up angle, and the types and positions of the laid film were used as test factors. For each planting line of 100 m, the front point of each line was defined as position 1, and 25 m from position 1 along the film-laying direction was defined as position 2; 50 m from position 1 along the film-laying direction was defined as sampling position 3. According to the film pick-up angle of the 1JRM-2000 curl-up film collector, the standard range of the film pick-up angle was determined to be 30–75◦. The table of test factor levels in the test on the curl-up force during film collecting is shown in Table 1.



3.2.2. Test Method

The tensile stress on the film was selected as the test index, which is calculated by Equation (7):

$$
\sigma = \frac{F}{bd} \tag{7}
$$

where *σ* is the tensile stress on the film, MPa.

In the test, the process of generating the curl-up force on the film with the curl-up film collector was simulated. Figure 7 shows the diagram of the operation process of the 1JRM-2000 curl-up film collector.

**Figure 7.** Operation process of the 1JRM-2000 curl-up film collector: 1—film, 2—film-curling mechanism, 3—film pick-up mechanism, 4—operation platform, 5—body frame, 6—traction mechanism, 7—deep limiter, 8—soil.

During operation, the variation range of the film pick-up angle is α1-α2. According to Figure 8, during the operation process of the curl-up film collector, the collected residue film would continually wrap around the film-curling device, increasing the film pick-up angle with the increase in the diameter of the residue film wrapping around the filmcurling device. The HP-50 digital display pull- and push-strength calculator was adopted to measure the curl-up force. During the force measurement, one end of the film was connected with the pull and push strength calculator, and the other end was at different angles with the ground to simulate the changing process of film pick-up angle during the curl-up collecting of film. The value of the film pick-up angle is controlled by the digital display angle ruler. When the film is initially pulled up, the soil on the film accumulates, and the film is subject to greater soil gravity. When the film is pulled up higher, the accumulation speed of the soil is similar to that of soil falling down from the film. At this time, the soil gravity is in dynamic equilibrium, and the curl-up force becomes stable. The digital display pull- and push-strength calculator was used to record the maximum value of the curl-up force in pulling up the film, and the obtained curl-up force was substituted into Equation (7) to calculate the tensile stress of the film.

**Figure 8.** Test field of curl-up collecting of film. (**a**) 11SM-1.2 curl-up film collector; (**b**) 1JRM-2000 curl-up film collector.

#### *3.3. Results and Analysis*

3.3.1. Results and Analysis of Contrast Test on the Tensile Properties of High-Performance Film and Ordinary Polyethylene Film

Table 2 shows the contrast test results of the tensile properties of the high-performance film and the ordinary polyethylene film laid in the Xinjiang cotton fields with a service period of 0–180 days.

Table 2 shows that the elongation at break and tensile yield stress of the high-performance film before and during use were higher than those of the ordinary polyethylene film; the elongation at break and tensile yield stress of the film with a thickness of 0.01 mm were higher than those of the film with a thickness of 0.008 mm. The tensile property of the film at a near-end position was higher than that of the film at a far-end position. When the sampling direction was horizontal, the elongation at break and tensile yield stress of the ordinary polyethylene film were higher than those when the film was collected vertically. For the high-performance film, and the elongation at break collected horizontally was higher than that collected vertically; its tensile yield stress was lower than that collected vertically. This is due to the different anisotropy of the high-performance film from the ordinary polyethylene film caused by the orientation of the macromolecules between the layers of the high-performance film. With the increase in the film-laying period, both the elongation at break and tensile yield stress of the high-performance film and ordinary polyethylene film decreased. The variation in the scales of the decrease in the elongation at break and tensile yield stress of the film is shown in Table 3. During the film-laying period of 0~30 days, the scales of the decrease in the elongation at break and tensile yield stress were higher than those during the film-laying period of 30~180 days. When the film-laying period was 120 days and 180 days, the scale of decrease in the elongation at break of the ordinary polyethylene film with a thickness of 0.01 mm collected horizontally at a far-end position and the high-performance film with a thickness of 0.008 mm collected horizontally at a near-end position were negative. This is caused by difference in the thickness of the film and different sampling positions, since the thickness error of film is +0.003~−0.002 mm. Each instance of sampling is located at that of the previous instance; thus, it may have little effect on the scale of decrease in the elongation at break of the film, which shows that there was little variation in the tensile property of the film when the film-laying periods were 90~120 days and 150~180 days.

