Detailed Explanation of Key Techniques for Full Seedling Emergence in a Single Sowing of Mulched Cotton

Baicheng City is located in the western part of Jilin Province and has a continental monsoon climate. To grow cotton there, the contradiction between the long cotton growth period and insufficient heat resources must be resolved. To achieve a bumper cotton harvest, the first essential step is to obtain full seedling emergence from a single sowing. In production, efforts must be made in adequate soil moisture, superior seed, fine sowing, film protection, and healthy seedlings, and the "five passes" must be strictly observed.

I. Land Preparation and Fertilization Pass

1. Soil selection: Cotton is a heat-loving crop. It is best to choose flat sandy (loamy) land for planting, with the previous crop preferably gramineous crops, soybean stubble, etc., which is relatively suitable for continuous cropping.

2. Irrigation to create soil moisture: Cotton seeds have weak sprouting vigor, so soil moisture favorable for cotton seed germination must be created artificially. Generally, pre-sowing irrigation is used to improve soil moisture. Plots without irrigation conditions should have ridges made on frozen soil to store water and conserve moisture.

3. Balanced fertilization: Although cotton tolerates poor soil, it is very fond of fertilizer. A yield of 50 kg of lint cotton per mu requires the absorption of 8 kg of nitrogen, 3 kg of phosphorus, and 6 kg of potassium. Therefore, balanced fertilization should be carried out according to soil fertility conditions. Organic fertilizer should be the main source, applied at 3000-4000 kg per mu, supplemented by chemical fertilizer, with base fertilizer applied as 10-15 kg of urea, 10-12 kg of diammonium phosphate, and 8-10 kg of potassium sulfate. For plots with good water and fertilizer retention, the nitrogen fertilizer intended for topdressing can also be applied as base fertilizer.

4. Fine land preparation: Cotton fields are best plowed in autumn; spring plowing should form ridges on frozen soil. After plowing, large ridges of 90 or 120 cm are formed to await sowing. Land preparation requires sufficient subsoil moisture, good surface moisture, a level and finely crushed surface without clods, and no straw, stubble, weeds, or residual film on the soil surface.

II. Seed Treatment Pass

1. Seed selection: It is advisable to choose early-maturing varieties with a growth period of 110-125 days and a pre-frost boll rate above 90%, such as early-maturing varieties Zhongmiansuo 36 and 42, Liaomian 17 and 18, etc. The black seed rate (healthy seed rate) should be above 80%; seed lots below 80% should undergo seed grading before sowing.

2. Sunning seeds: 10-15 days before sowing, choose sunny days and sun the seeds continuously for 4-5 days. This can promote after-ripening of seeds, increase the germination rate, and also has a sterilizing effect and reduces disease.

3. Soaking seeds: Two days before sowing, soak the seeds in cool water for 24 hours, soaking them thoroughly and evenly, until the cotton kernel can be squeezed out by hand. Then drain and dry them. Seeds that have been delinted with sulfuric acid do not need soaking.

4. Seed dressing: Seed dressing before sowing is mainly for the prevention and control of pests and diseases. For every 50 kg of seeds, use 100 g of carbofuran and 200 g of dexon or Kubiqing for seed dressing. First dress with fungicide, then with insecticide. After sealing for 24 hours, spread out to dry and await sowing.

III. Sowing Quality Pass

1. Timely sowing: Cotton seedlings have poor tolerance to low temperatures, but sufficient growth period must also be ensured. Therefore, sowing should be timely. Generally, sowing from April 20-30 is appropriate, and no later than May 5.

2. Dibbling for precise spacing: On the formed sowing ridge surface, open sowing furrows 10-13 cm deep. Open 2 rows on 90 cm ridges and 3 rows on 120 cm ridges. Dibble seeds in the sowing furrows, 6-8 seeds per hill, with a plant spacing of 13-18 cm. Determine density according to the principle of "sparser on fertile land, denser on poor land." For plots with poor soil moisture, water to raise moisture, then cover the seeds with 2-3 cm of fine soil.

3. Spraying for weed control: After sowing and covering with soil, use herbicide to seal the ridge surface to prevent and control weeds. Apply 250 g of 40% "Lasso" or 45 mL of 90% "Harness" per mu, diluted with 20-40 kg of water, evenly sprayed on the ridge surface, then promptly cover with film.

4. Film mulching to increase temperature: Film mulching must ensure quality. Pay attention to stretching it lengthwise, making it flat and straight, achieving a film as flat as a mirror, so it cannot be lifted by wind or damaged by gusts. After mulching, there should be a 7-10 cm gap between the sowing furrow and the film to prevent the film from burning seedlings after emergence.

IV. Mulch Film Protection Pass

1. Press down the film-covering soil well: Da'an City has many strong winds in spring, which can easily lift the plastic film and cause it to lose its functions of increasing temperature and conserving moisture. Therefore, special attention must be paid to protecting the film. After mulching, press a shovel of soil on the ridge surface every 2-3 m, or use convenient bags filled with soil to press down the film.

2. Irrigate the film-pressing water well: After sowing, lightly irrigate once in the furrow to press the film, so that the soil on both sides of the film is moistened and strong winds cannot lift the film. For cotton fields with relatively moist soil, try not to irrigate, to prevent low soil temperature after irrigation from causing damping-off disease.

3. Watch over the mulched field well: Mulched cotton fields are easily trampled by livestock and poultry and pecked by birds, and are also easily lifted by strong winds. Therefore, the field must be frequently inspected and the plastic film protected in a timely manner.

V. Seedling Protection and Vigor Pass

1. Ventilation to release seedlings: When about 80% of cotton seedlings have emerged, poke a ventilation hole every 2-3 m. After 3-4 days, poke a ventilation hole above each seedling eye the thickness of a five-fen coin to harden the seedlings. After the final frost (generally around May 15-20), release the seedlings while avoiding the high-temperature period at noon. Release 2-3 plants per hill; for plots with lighter pests and diseases, release 1-2 plants. Straighten the cotton seedlings and seal them firmly with soil to prevent temperature drop after ventilation and the growth of weeds.

2. Thinning and final singling of seedlings: Timely thinning and final singling can promote early development of small seedlings and prevent "tall-legged seedlings" and weak seedlings. Thin seedlings at 1-2 true leaves, and finalize seedlings at 2-3 true leaves, leaving 1 plant per hill. Final singling must be completed by the end of May.

If low temperatures occur after releasing seedlings and humidity under the film is high, damping-off disease is likely to occur. Kubiqing or mancozeb can be sprayed 1-3 times, while adding foliar fertilizer such as "Pushibao" to promote healthy seedling growth.