Field Crop 2025, Vol.8, No.4, 195-203 http://cropscipublisher.com/index.php/fc 197 Figure 1 Schematic diagram of different planting patterns of machine-harvested cotton (Adopted from Gao et al., 2024) 3.2 Relationship between row spacing, root distribution, and nutrient use efficiency Row spacing not only affects the growth of the above-ground part of cotton, but also influences the distribution of the underground root system. This will affect the cotton's ability to absorb water and nutrients. If the row spacing is uniform, the root system will be distributed more evenly, and there will be less competition among the plants, which can help cotton absorb more water and nutrients. However, if the rows are wide or narrow, the root systems may be concentrated in certain areas. In this way, the water and nutrients in these areas of the soil will be used up very quickly. Research has found that when uniform row spacing is combined with appropriate density, the water use efficiency (WUE) of cotton is the highest, especially at high density, the effect is more obvious. If wide and narrow rows are used but planted sparsely, the plants will not compete too much for water and nutrients, allowing the root system to extend more fully and also improving the WUE. This approach is particularly useful in cases of water shortage]. In addition, in the case of drip irrigation, the difference brought by this row spacing will be more obvious. Because drip irrigation can precisely water and fertilize based on the distribution of roots, its efficiency will be higher. 3.3 Influence of row configuration on fiber maturity and uniformity The design of line spacing can also change the maturity and consistency of cotton fibers by influencing the microclimate of the canopy. Although high-density combination with wide and narrow rows can increase production, if the canopy is too dense, light cannot reach the bottom, which can easily cause poor development of the lower cotton bolls and a decline in fiber quality. Under conditions of sufficient moisture, uniform row spacing can improve the lighting environment in the middle and lower layers, allowing the cotton bolls to develop better, and both the length and strength of the fibers can be enhanced, making them more mature and consistent. This is because the light distribution is more uniform, providing better development conditions for cotton bolls (Zuo et al., 2024). In addition, some planting methods, such as high-density wide rows, can also reduce leaf residue, accelerate the rate of leaf drop, and are helpful for improving the fiber quality of machine-picked cotton. 4 Interactive Effects of Density and Row Configuration 4.1 Combined effects of planting density and row spacing on plant architecture Planting density and row spacing interact with each other, thereby altering the structure of cotton plants, including canopy morphology, light distribution and the position of cotton bolls. High-density wide and narrow rows (such as 66 cm+10 cm) can enable the upper canopy to close more quickly, enhance photosynthetic activity, and help increase lint cotton yield, especially in water-scarce environments. On the contrary, moderate density combined with uniform row spacing (such as 76 cm) can make it easier for light to enter the middle and lower parts of the canopy, while increasing the leaf area index (LAI). This is conducive to increasing the biomass of cotton bolls and
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