Detailed Explanation of Agronomic Supporting Techniques for Drip Irrigation Under Plastic Mulch in Cotton

Drip irrigation under plastic mulch is a technique that combines drip irrigation technology with plastic film mulching cultivation technology. Water is supplied through a controllable pipeline system; after water and fertilizer are mixed, they are delivered drop by drop evenly, at set times and in set amounts, moistening the crop root development zone and always keeping the root-zone soil loose and at optimal moisture. It reduces evaporation between crops and improves water use efficiency.

1. Irrigation regime

For subsurface drip irrigation, total water use was 175.48 million cubic meters. Dripping was done 9 times. For precision drip irrigation, total water use was 177.84 million cubic meters. Dripping was done 8 times. During drip irrigation, an irrigation regime was formulated according to **the water requirement patterns of cotton at each growth stage. It has practical value for drip irrigation planning, drip irrigation cycles, irrigation zones, irrigation quotas, and duty systems, and provides guidance for cotton production, meeting the cotton's water needs. It follows the principle of irrigating according to the cotton growth period: less in the early stage, ample in the middle stage, and supplementary in the late stage. The first drip irrigation was in late June (squaring stage), with an irrigation quota of 12 cubic meters/mu at the squaring stage. In July, during the flowering and boll stage, drip irrigation was done 3-4 times, with an irrigation quota of 22 cubic meters per mu. In August, during the boll stage, drip irrigation was done once every 10 days, with an irrigation quota of 15 cubic meters per mu. In early September, the last drip irrigation was done, with an irrigation quota of 10 cubic meters per mu. Over the entire growth period, irrigation totaled 200-250 cubic meters.

To give full play to the water-saving and yield-increasing effects of drip irrigation under plastic mulch, irrigation under the mulch must be adapted to time, place, and seedling conditions. Under measurement with a Shengtepu moisture meter, subsurface drip irrigation showed little change in soil moisture at 0-10CM below the surface, with the surface basically dry, preventing water loss, keeping the lower part of the cotton plant dry for a long time, and reducing the occurrence of pests and diseases and boll rot. Under measurement with a Shengtepu moisture meter, surface drip irrigation showed rapid water loss at 0-10CM below the surface. Subsurface drip irrigation concentrated the irrigation water at 30-60CM, while surface drip irrigation concentrated the irrigation water at 10-40CM. From excavating and washing root systems on July 17, the cotton root distribution range differed under the two methods. Under subsurface drip irrigation, cotton roots developed narrowly and deeply, with the main roots distributed at 10-50CM, few fibrous roots, and slender roots. Under surface drip irrigation, roots developed widely and shallowly, with the main roots distributed at 10-30CM, many fibrous roots, and short, thick roots. Because the water required for cotton growth is replenished into the soil at multiple levels, root development differs. According to different soil types, the amount of water per drip irrigation should not be too large; too much water easily causes compaction of the soil plow layer, worsens soil aeration, makes soil water, fertilizer, air, and heat conditions uncoordinated, causes cotton root rot, and is unfavorable to cotton root growth.

2. Fertilization management

As the irrigation method changed, fertilization measures also changed accordingly. The technique of fertilizing with water synchronizes water and fertilizer, keeping the cotton field water as a nutrient solution, so nutrients are less adsorbed and fixed by the soil and are evenly distributed in the soil; cotton absorbs nutrients while absorbing water. In terms of dosage, apply few times but in large amounts. When applying nitrogen fertilizer, first apply 50% of the total nitrogen fertilizer as base fertilizer, and the rest can be applied with drip irrigation water. Apply nitrogen fertilizer 2-3 times over the whole growth period, with each application of 3-5kg. Apply cotton special fertilizer 2-3 times, with each application of 3-5kg. When applying nitrogen fertilizer, consider the temperature during the growth period, promptly grasp the cotton fertilizer requirement patterns, fully coordinate the water-fertilizer ratio, prevent fertilizer loss, and give full play to the utilization rate of nitrogen fertilizer. For phosphorus fertilizer dosage, apply it all at once into the base fertilizer. Spray foliar fertilizer 3-4 times. When dripping water for cotton, prepare the ratio according to the nutrients required at different cotton growth stages, and supply the cotton timely and in appropriate amounts, ensuring that cotton growth saves a large amount of fertilizer and water and fully improving fertilizer use efficiency.