How Does Cotton Photosynthetic Efficiency Change Under Different Planting Methods

To further increase cotton yield, it is difficult to achieve this by merely increasing the number of plants per unit area. In production, while increasing density, it is necessary to improve the poor ventilation and light transmission in the middle and lower parts of the cotton population, and increase the light transmission rate and photosynthetic efficiency in the middle and lower parts of the cotton population. Through research on the photosynthetic efficiency and light transmission rate of cotton populations under different planting methods, this paper aims to determine a reasonable cotton population structure for a specific region, providing a basis for high-yield and high-quality cotton cultivation.

I. Materials and Methods

1. Experimental Overview

The experiment was conducted from 2002 to 2003 at the Agronomy Experimental Station of Shihezi University. The experimental field had medium fertility, with cotton as the previous crop. The cotton variety tested was Zhongmiansuo 36, and the sowing date was April 29.

2. Experimental Design

Cotton planting densities: 10,000 plants/667 sq m, 15,000 plants/667 sq m, 20,000 plants/667 sq m, with a row spacing of 60 + 30 cm wide-narrow rows.

Topping treatments: Each density was divided into 3 treatments: 1 topping (July 10), 2 toppings (July 10, 25), and 3 toppings (June 25, July 10, 25) (hereinafter, topping methods are all expressed as 1 topping, 2 toppings, 3 toppings), arranged in randomized blocks with 3 replications. The plot area was 30 sq m, 5 m wide from north to south and 6 m long from east to west. Film mulching cultivation was adopted, using the planting method of laying film first and then dibbling. During the growth period, the field was kept free of weeds, and other management was the same as the field.

Topping sequence: The 1-topping treatment refers to removing the growing tips of all cotton plants at one time on July 10. The 2-topping treatment refers to removing the growing tips of cotton plants in the middle two rows on July 10, and removing the growing tips of cotton plants in the two outer rows on July 25. The 3-topping treatment refers to removing the growing tips of cotton plants in any 1 of the middle two rows on June 25, removing the growing tips of cotton plants in the other middle row on July 10, and removing the growing tips of cotton plants in the two outer rows on July 25.

3. Test Items

Photosynthetic rate was measured using an infrared carbon dioxide analyzer at 3 stages: early flowering, full boll stage, and boll opening stage. For each treatment, 3 representative sampling points were selected, and the photosynthetic rate of the cotton population was measured at 12:00 noon on sunny days.

Light transmission rate was measured using an illuminometer during the full boll stage of cotton. For each treatment, representative sampling points of 80 x 90 cm were selected, and 9 treatments were measured simultaneously at 12:00 noon on sunny days. Each sampling point was measured layer by layer using a vertical pole with stretched lines (one layer every 10 cm), with 17 points measured in each layer, measured from bottom to top and from outside to inside respectively, and all obtained data were processed by computer.

II. Results and Analysis

1. Changes in Photosynthetic Rate at Each Growth Stage Under Different Planting Methods

For the photosynthetic rate of cotton populations under different planting methods, at the early flowering stage, the population photosynthetic rate was highest under the 20,000 plants/667 sq m density with the 2-topping method. In addition, compared with the other two topping methods at the same density, the population photosynthetic rate under the 20,000 plants/667 sq m density with the 2-topping method was the highest, followed by the population photosynthetic rate under the 1-topping treatment, and then the population photosynthetic rate under the 3-topping treatment. This is mainly because the leaf distribution of the cotton population formed by 1 topping and 3 toppings was unreasonable, showing a phenomenon of too many or too few leaves, causing differences in the photosynthetic rate of the cotton population. From this, it can be seen that at the early flowering stage, the population photosynthetic rate was highest under the 20,000 plants/667 sq m density with the 2-topping method.

For the photosynthetic rate of cotton populations under different planting methods, at the full boll stage, the 2-topping method was higher than the other two topping methods at the same density, among which the population photosynthetic rate under the 10,000 plants/667 sq m density with the 2-topping method was significantly higher than the other two topping methods at the same density. Overall, at the full boll stage, the 20,000 plants/667 sq m density with the 2-topping method was relatively reasonable, and the population photosynthetic rate reached a relatively ideal state.

For the photosynthetic rate of cotton populations under different planting methods at the boll opening stage, the population photosynthetic rate under the 2-topping method was significantly higher than the other two topping methods at the same density.

For the cumulative photosynthetic rate of cotton populations at the early flowering stage, full boll stage, and boll opening stage under the 3 densities, the value was the largest under the 20,000 plants/667 sq m density with the 2-topping method, and the lowest under the 10,000 plants/667 sq m density with the 3-topping method. This is mainly because competition among plants in the 10,000 plants/667 sq m density population was relatively small, among which the cotton plants in the middle row topped on June 25 were short, and the disadvantage of the outer rows reached a relatively large value, with extremely low photosynthetic efficiency, thereby causing a decrease in the population photosynthetic rate.

2. Effects of Different Planting Methods on Population Light Transmission Rate

The canopy light transmission rate of cotton populations under different planting methods all showed that the canopy light transmission rate decreased as canopy height decreased, and the light transmission rate of cotton plants in the canopy above 40 cm decreased relatively slowly; among the 3 densities, the light transmission rate under the 2-topping method changed greatly in the 40 to 70 cm canopy and was relatively concentrated, while below 40 cm the light transmission rate changed gently. In particular, the change in light transmission rate of the cotton population under the 20,000 plants/667 sq m density with the 2-topping method was more consistent with this pattern, indicating that the canopy light transmission rate of the cotton population under the 20,000 plants/667 sq m density with the 2-topping method was more reasonable.

3. Effects of Different Planting Methods on Lint Yield

The level of cotton yield determines the utilization of light energy by the cotton plant population. A reasonable population can both fully exert the best productivity of individual plants in the population and give play to the population's yield-increasing potential. Density has a significant effect on the number of cotton fruiting branches and boll weight per plant, while different topping methods cause changes in the hierarchy of the cotton canopy, affecting the light transmission of cotton plants. The combined effect of the two treatments directly affects the final cotton yield.

Through the measurement of cotton yield under the same density with different topping methods and the lint yield of cotton plots under different planting methods, it was shown that among the cotton lint yields under different topping methods at the 3 densities, the highest was under the 20,000 plants/667 sq m density with the 2-topping method, at 136.732 kg/667 sq m. In addition, after the density increased from 10,000 plants/667 sq m to 20,000 plants/667 sq m, yield showed an obvious increasing trend with increasing density. This indicates that, through the treatment of different planting methods, Zhongmiansuo 36 had a relatively reasonable population structure under the 20,000 plants/667 sq m density with the 2-topping method.

III. Brief Summary

1. For cotton populations under different planting methods, the photosynthetic rate at the 3 stages of early flowering, full boll stage, and boll opening stage was highest under the 20,000 plants/667 sq m density with the 2-topping method. It can be seen that the cotton population under the 20,000 plants/667 sq m density with the 2-topping method had relatively great photosynthetic potential.

2. The light transmission rate of cotton under different planting methods decreased as plant height decreased. Under the 20,000 plants/667 sq m density with the 2-topping method, the light transmission rate in the 40 to 70 cm canopy was relatively concentrated, and below 40 cm the light transmission rate changed gently. In production, fruiting branches should be concentrated above 40 cm as much as possible.

3. Among the cotton lint yields under different planting methods, the highest was under the 20,000 plants/667 sq m density with the 2-topping method.