Key Techniques for Water-Saving Cotton Cultivation in Semi-Arid Saline-Alkali Land

Cotton has always been an important economic crop, and continuously improving cotton yield and quality is of great significance for increasing agricultural efficiency and farmers' income. Over the years, through gradual exploration, a relatively complete set of cotton cultivation techniques for semi-arid saline-alkali land has been developed, achieving the goals of early maturity, high yield, and high quality in drought-resistant cotton planting. This has solved the problems of difficult emergence, difficult seedling retention, slow development, and late maturity when planting cotton in saline-alkali land due to lack of water resources.

The cotton yield-increasing techniques for semi-arid saline-alkali land mainly include seed preparation, fertilization, chemical control, pruning, and other steps.

Seed preparation:

Select insect-resistant cotton varieties that are resistant to cotton bollworm, drought, premature senescence, waterlogging, tolerant to poor soil, and tolerant to saline-alkali conditions, such as the nationally approved Ji 668, Ji 669, Guoxin Cotton No. 3, Jifeng 197, etc.

Determination of seeding rate: The seeding rate per mu should be larger than that for plots with good water and fertilizer conditions. For mechanically sown cotton fields, the seeding rate should be about 2 kg per mu, with no fewer than 3 to 4 seeds per hill; for manually dibbled cotton fields, the seeding rate should be about 1.5 kg. Only with a sufficient seeding rate can adequate seedling density be ensured. Note: 1. Before sowing, a germination test must be done, and the appropriate seeding rate determined according to the germination rate. 2. Coated seeds must not be soaked before sowing; they should be sown dry. 3. Sunning seeds before sowing can promote after-ripening, increase the germination rate, and also sterilize and reduce seedling diseases.

Adopt plastic film mulching technology

Plastic film mulching has the effects of increasing temperature, preserving soil moisture, raising moisture from deeper layers, promoting early seedling growth, preventing weeds, and inhibiting soil salinization. Saline-alkali plots tend to return salt to the surface, which is unfavorable for cotton emergence and early seedling growth, and often due to late boll setting, there are fewer bolls before frost, resulting in poor cotton quality, low yield, and low benefits. This problem can be solved through plastic film mulching. Production practice has proven that film-mulched cotton grows significantly faster than open-field cotton and has an obvious drought-resistant effect. Film-mulched cotton has more bolls before frost and good quality. When planting film-mulched cotton, note: sowing depth should be shallower, generally about 3 cm.

Sow at the appropriate time

The timing of sowing is extremely important for early, complete, uniform, even, and strong cotton seedlings. For semi-arid plots, the sowing time for film-mulched cotton should be from April 20 to April 25; open-field cotton should be sown after April 25 and finished around May 1. Be careful not to sow too early, to avoid low-temperature chilling injury, seed rot, sprout rot, and seedling diseases.

Rational close planting

Semi-arid saline-alkali land has poor soil fertility, cotton does not grow vigorously, plants are short, and the growth period is short, so high yield must be obtained through a large population, and seedlings should be retained at appropriately higher density. This can increase the number of bolls near the main stem, thereby improving yield and quality. Generally, 3500 plants/mu to 4000 plants/mu should be achieved. Also, different varieties have different densities because of differences in plant architecture compactness; compact varieties can be slightly denser, while loose varieties can be slightly sparser. A wide-narrow row planting pattern is better, with wide rows 80 cm, narrow rows 50 cm, and an average row spacing of 65 cm.

Balanced fertilization

Balanced fertilization can both improve fertilizer use efficiency and promote cotton root extension downward, allowing absorption of deep soil moisture and thus playing a role in water saving and drought resistance. To achieve high yield and high quality of cotton in semi-arid saline-alkali land, various nutrients needed for cotton plant growth must be continuously supplied through fertilization. Increasing basal fertilizer and building soil fertility are important measures, with basal fertilizer as the main part and topdressing as the supplement. Basal fertilizer should be mainly organic fertilizer, combined with nitrogen, phosphorus, and potassium; topdressing should heavily apply flowering and boll fertilizer, with an obvious yield-increasing effect. To reach a seed cotton yield of 250 to 300 kg per mu, it is recommended to apply per mu as basal fertilizer: 2 cubic meters of organic fertilizer, 10 to 15 kg of urea, 20 kg of diammonium phosphate, and 10 to 15 kg of potassium sulfate. During the cotton flowering and boll stage, topdress an additional 15 kg of urea. In the middle and late stages, use per mu 0.5 to 1.0 kg of urea, 0.2 kg of monopotassium phosphate, or 15 mL of Fuwanjia, plus a small amount of boric acid, diluted with 50 kg of water for spraying, once every 7 to 10 days, for a total of 2 to 3 sprays.

Pruning and removal of excess branches

For dryland cotton cultivation, the key is timely pruning and removal of excess branches, especially removing excessive vegetative branches, topping the main stem, and topping the fruiting branches. Excess vegetative branches below the first fruiting branch should be removed in time. Topping the main stem is generally done before July 15, leaving 10 to 13 fruiting branches per cotton plant. Topping the fruiting branches should generally be completed before August 10. On each fruiting branch in the lower part of the cotton plant, 2 to 3 fruiting nodes can be retained; in the middle part, 3 to 4 fruiting nodes can be retained on each fruiting branch; and in the upper part, 2 to 3 fruiting nodes can be retained on each fruiting branch.

Chemical control techniques for cotton

This includes two aspects: controlling excessive growth with mepiquat chloride and promoting ripening with ethephon. When using mepiquat chloride, the dosage must be strictly controlled and applied flexibly according to variety, climate, soil texture, and growth condition. Under normal circumstances, during the entire cotton growth process, chemical control is applied 3 to 4 times: the first chemical control is at the full bud stage or early flowering stage, with a mepiquat chloride dosage of 0.5 to 1 g per mu; the second chemical control is at the full flowering stage, with a dosage of 2 to 3 g; the third chemical control is at the flowering and boll stage, with a dosage of 3 to 4 g.

In the late growth stage of cotton, autumn temperatures drop relatively quickly, and some late bolls often cannot mature naturally, or even cannot crack and fluff. Ethephon can be used to promote faster boll maturation, increase the number of bolls before frost, and improve yield and quality.

Control of cotton diseases and insect pests

Diseases: mainly seedling diseases, fusarium wilt, verticillium wilt, etc. Seed coating with seed dressing agents can effectively control seedling-stage diseases. Fusarium wilt and verticillium wilt can be controlled through comprehensive measures such as crop rotation, selection of disease-resistant varieties, and timely removal of diseased plants.

Insect pests: mainly control aphids, red spiders, mirids, thrips, and other pests. Attention should be paid to the control of mirids, with control timing in the evening. In years with severe cotton bollworm occurrence, chemical control should be applied 1 to 2 times at the peak of each generation, with the control threshold being 20 second-instar larvae per 100 cotton plants.