The double-film-covered double-overlay cotton-growing technique is an innovative approach to re-covering the narrow membrane at the planting row on a standard wide-membrane setup (both membranes are mechanically applied). In our area, the regular mulch film used is 0.008 mm thick and 1.25 m wide, with a row spacing of 66+10 cm for machine-planted cotton. The upper layer is a narrower membrane, 0.4 m wide and 0.004 mm thick, which covers the individual rows. The total film usage per hectare is about 25.5 kg, which increases the cost by approximately 400 yuan. Adding an extra layer of film over the seed rows helps prevent soil compaction after rain and raises ground temperature, creating a more favorable 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. This often leads to replanting each year. To address this issue, we began researching the double-film coverage technique in 2004, and after years of testing and refinement, the double-film-covered double-soil-covered method was widely adopted in our region in 2007. However, during large-scale application, several challenges have emerged that need improvement.
First, there are several issues:
1. **Delayed Seedling Emergence**: Although double-film-covered cotton seeds emerge earlier, their growth is slower compared to conventional methods. This was especially noticeable in 2007 due to prolonged low temperatures in spring, leading to significant temperature differences inside and outside the films, which negatively affected seedling development.
2. **Lower Germination Rate**: Many fields use dual-layer coverage to prevent soil crusting and improve survival rates. However, with limited spring rainfall, the benefits of the technique are not always clear, and in some cases, germination rates are lower than expected.
3. **Excessive First Cover Soil**: Initially, no first-layer cover was used, requiring manual sealing after emergence, which was labor-intensive. Now, a first-layer mechanical cover is applied during sowing, reducing labor. However, in some areas, the cover is too thick, leading to poor emergence and increased root rot.
4. **Thick Secondary Cover Causing Pressure**: To prevent the small membrane from being blown away, the secondary cover is often too thick, pressing down on the seed line. In some cases, the entire seed line is buried, making it hard for seedlings to emerge.
5. **Misaligned Seed Holes**: When the small membrane is pressed, it can cause the larger membrane to shift, resulting in misalignment of the seed holes.
6. **Deep Sowing Depth**: Due to deep soil preparation, the seed depth is too deep, and wet conditions at sowing time can affect germination.
7. **Excessive Drip Irrigation**: Too much water from drip irrigation can saturate the cover soil, causing compaction once the film is removed.
8. **Delayed Film Removal**: Seedlings must be uncovered before they become visible, and if the film is removed too late, it can lead to higher mortality due to temperature fluctuations.
To address these issues, several improvements have been made:
1. **Early Film Removal**: Remove the film when seedlings are 20% to 30% up, or manually punch the small film to reduce internal temperature differences and speed up emergence.
2. **Adjust First-Layer Cover Thickness**: Keep the first cover soil no thicker than 1 cm to avoid hindering seedling growth.
3. **Control Secondary Cover Thickness**: Avoid excessive pressure on the seed line by adjusting the thickness and increasing the distance between the secondary cover and the seed row.
4. **Ensure Proper Alignment**: Laying the first-layer film correctly and preparing the soil appropriately can help prevent seed hole misalignment.
5. **Moderate Drip Water Application**: Avoid overwatering, as it lowers soil temperature and increases the risk of disease. Excessive moisture can also create "bottle" knots in the soil, which hinder seedling growth.
Finally, some key considerations:
1. For sandy and loamy soils with good quality, the double-film-covered double-overlay technique can be used to reduce costs.
2. In later sowing areas, if heavy rain is not 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 increase costs and reduce efficiency. It’s important to adapt the method based on local conditions and weather forecasts for optimal results.
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