Detailed Explanation of Key Technical Points for Drip Irrigation and Fertigation under Cotton Mulch

Drip irrigation under cotton mulch is a new water-saving technology that allows artificial control of irrigation volume and field microclimate, greatly alleviating the **tension of water use for the first irrigation, and can control the reproductive growth and vegetative growth of cotton, helping to shape an ideal plant architecture and reduce ineffective nutrient consumption. Although some problems still exist in practical application, cotton under drip irrigation generally opens bolls earlier, has better quality and higher yield. At the same time, under special climatic conditions, drip irrigation has demonstrated unique cold resistance. When encountering special low-temperature conditions in spring and autumn, growth and development remain normal, with strong high and stable yield, and a relatively concentrated maturity period.

I. Drip Irrigation under Mulch

Drip-irrigated cotton fields under mulch should follow the laws of cotton growth and development, that is, less water at the seedling stage, increased water at the bud stage, and peak water demand at the flowering and boll-setting stage. Drip irrigation should follow the principle of "small amounts and frequent applications, frequent and light irrigation." Never apply too much water at one time, to avoid surface runoff and failure to achieve water-saving effects.

1. Apply drip irrigation 10-11 times during the growth period, in principle once every 7-10 days. In mid-to-late June, apply 35-40 cubic meters per 667 sq m. After 10 days, apply another irrigation of 25-30 cubic meters per 667 sq m. In July, apply drip irrigation 4 times, preferably at 7-day intervals, with 25-30 cubic meters per 667 sq m each time. In August, apply 3 times, once every 10 days, with 20-30 cubic meters per 667 sq m each time. After the last irrigation in early September, stop irrigation; apply 15-20 cubic meters per 667 sq m. During the growth period, apply 235-310 cubic meters per 667 sq m. For late-maturing varieties and cotton fields with excessively vigorous growth, use the lower limits for the total drip irrigation amount per 667 sq m and for each application; for early-maturing varieties and cotton fields with weaker growth, use the upper limits for the total drip irrigation amount per 667 sq m and for each application.

2. The first drip irrigation must adopt the two-pass drip irrigation method, dividing the first drip irrigation into two applications (crops generally have stronger vertical infiltration than horizontal infiltration. According to experience from various regions, if the first irrigation does not infiltrate to the edge of the rows, subsequent irrigations will also find it difficult to infiltrate thoroughly. Therefore, increase the drip irrigation amount of the first irrigation, start drip irrigation 3-5 days earlier, increase the bottom soil moisture, and alleviate later pressure). Bundled drip irrigation can be used, connecting two adjacent plots together. After the first drip irrigation, the vertical porosity of the soil is greatly reduced, and when the second drip irrigation is applied, horizontal infiltration is noticeably faster. Dividing into two applications facilitates horizontal infiltration, makes crop irrigation uniform, and can prevent continuous dripping of the same amount of water in the same direction, which causes severe deep percolation, making the middle rows of cotton tall and the edge rows short, resulting in uneven growth.

3. For plots with a more sandy texture, apply one additional drip irrigation to ensure uniform growth of the cotton field. Strictly control the number of drip irrigations and the amount per 667 sq m, and prevent reducing the number of drip irrigations because the amount per 667 sq m is too large.

4. Adjust measures according to local conditions, judging by weather, soil and seedling conditions. Generally, stop irrigation in early September.

II. Fertigation under Mulch

1. For cotton fertigation, select suitable drip irrigation fertilizers based on the soil texture of the drip-irrigated field. For nitrogen fertilizer, mainly use urea; for phosphorus fertilizer, choose potassium dihydrogen phosphate to improve the utilization rate of potassium fertilizer.

2. Apply chemical fertilizers by drip during the middle period of irrigation, dividing one irrigation cycle into 3 stages for control. In the 1st stage, wet the soil with water containing no chemical fertilizer, for about 1 hour; in the 2nd stage, add the calculated amount of chemical fertilizer into the water at the appropriate time, so that the aqueous solution is distributed in the soil layer through the system, for about 4-5 hours; in the 3rd stage, stop fertilization and continue drip irrigation for 0.5 hour, which serves to clean the irrigation pipeline system and prevent corrosion of the pipes and clogging of the emitters. The amount of fertilizer applied by drip per 667 sq m each time should be determined according to the amount of fertilizer remaining after whole-layer fertilization. If 25 kg of urea and 1.8 kg of potassium dihydrogen phosphate remain per 667 sq m during the growth period, they should be applied in divided amounts with drip irrigation according to the cotton growth and development process. In mid-to-late June, the first fertigation is from the full bud stage to the early flowering stage, applying 4 kg of urea plus 0.2 kg of potassium dihydrogen phosphate per 667 sq m; in early July, the second fertigation is from the early flowering stage to the full flowering stage, applying 8 kg of urea plus 0.5 kg of potassium dihydrogen phosphate per 667 sq m; the third fertigation is in mid-to-late July, applying 6 kg of urea plus 0.5 kg of potassium dihydrogen phosphate per 667 sq m; the fourth fertigation is from late July to early August, applying 4 kg of urea plus 0.3 kg of potassium dihydrogen phosphate per 667 sq m; the fifth fertigation is in early August, applying 3 kg of urea plus 0.3 kg of potassium dihydrogen phosphate per 667 sq m.

3. It is strictly prohibited to apply fertilizer with every irrigation, to prevent excessive vegetative growth in the early stage and delayed maturity due to excessive late-season growth. The first drip irrigation, the drip irrigation after topping, the drip irrigation in mid-August, and the drip irrigation in early September must not carry fertilizer.

4. When applying fertilizer with drip irrigation, there must be no water leakage or water loss, and drip irrigation must be uniform; otherwise, it easily causes uneven cotton growth and brings difficulties to later chemical regulation and pruning.