The double-film-covered double-overlay cotton-growing technique is an innovative method designed to re-cover narrow membranes at the planting rows on a regular wide-membrane system, with both layers applied mechanically. In our region, the standard mulch film used is 0.008 mm thick and 1.25 m wide, with a row spacing of 66+10 cm for machine-sown cotton. The upper layer is a narrower membrane, 0.4 m in width and 0.004 mm thick, which covers the crop rows. The total amount of film per hectare is about 25.5 kg, increasing the cost by approximately 400 yuan. This technique helps prevent soil compaction after rain and raises ground temperature, creating a better environment for cotton seedlings to emerge.
Our field has a large area of saline soil that tends to harden after rainfall, making it difficult for seedlings to break through. As a result, we often have to replant each year. To address this issue, since 2004, we organized technical teams to research and develop the double-film coverage method. After years of trials, improvements, and demonstrations, the technology was widely adopted in our district by 2007. However, during large-scale application, several challenges remain that need further refinement.
First, there are several issues:
1. **Slow seedling emergence**: Although double-covered cotton emerged first, the growth was delayed due to lower temperatures in spring 2007, leading to weaker seedlings. The temperature difference inside and outside the film caused stress, affecting early development.
2. **Lower emergence rate**: Many fields were covered with two layers of film to prevent soil crusting, but with less spring rain, the benefits were not always clear, and in some cases, the emergence rate was worse than conventional methods.
3. **Thick first-layer cover soil**: Initially, no first-layer cover was used, requiring manual sealing after the small membrane emerged, which was labor-intensive. Later, a mechanical first-layer cover was introduced, reducing effort. However, in some areas, the cover was too thick, causing poor emergence and root rot.
4. **Excessive secondary cover soil**: To prevent the small membrane from being blown away, the second layer was often too thick, pressing down on the seed line and even burying it completely, making it hard for seedlings to emerge.
5. **Misaligned seed holes**: When the small membrane was pressed, it sometimes shifted, causing misalignment of the seed holes.
6. **Deep sowing depth**: Due to deep soil preparation and wet conditions during sowing, the seed depth became too deep, affecting germination.
7. **Overwatering via drip irrigation**: Excessive water led to saturated cover soil, causing compaction once the film was removed.
8. **Delayed film removal**: If the film wasn't removed in time, seedlings faced higher temperature fluctuations, resulting in more deaths.
To improve these issues, several measures have been taken:
1. **Early film removal**: Remove the film when 20–30% of the seedlings are visible, or manually punch holes to reduce internal temperature differences and speed up emergence.
2. **Adjust first-layer cover thickness**: Keep it under 1 cm to avoid over-covering the seeds.
3. **Optimize secondary cover**: Reduce its thickness and increase the distance between the cover and the seed rows.
4. **Improve alignment**: Ensure the first-layer film is laid properly, with appropriate soil preparation depth.
5. **Control drip irrigation**: Avoid excessive watering to prevent low ground temperatures and moisture-related issues like "bottle neck" formation.
Finally, some key considerations:
- For sandy and loamy soils with good quality, the double-film method can be used to cut costs.
- In later sowing seasons, if no heavy rain is expected, double-film coverage may not be necessary.
While the double-film-covered double-overlay technique is effective in improving seedling emergence, improper use can lead to increased costs and reduced efficiency. Proper implementation and adjustment based on local conditions are essential for success.
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