Growth Characteristics and Fertilizer-Water Management Methods of Cotton at the Squaring Stage

Growth characteristics of cotton at the squaring stage. From the appearance of squares, cotton enters a period in which vegetative growth and reproductive growth proceed together, but vegetative growth still predominates. The photosynthates produced during the squaring stage are mainly transported to the vigorously growing parts of the main stem and the tips of the fruiting branches, and very little is supplied to the squares. As air temperature continues to rise, the growth of cotton roots, stems, leaves, fruiting branches and flower buds markedly accelerates, plant metabolism becomes increasingly vigorous, physiological activity intensifies, photosynthetic productivity is high, and root growth reaches its peak period. Management at this stage is mainly aimed at strong plants with steady growth, building a good high-yield framework.

Growth appearance of normal cotton during the squaring stage. During the squaring stage, cotton should be "strong but not excessively vigorous, steady but not declining," that is, on the basis of strong seedlings and early development, strong plants with steady growth, ensuring both a well-developed root system and robust plants with large and numerous squares, while preventing excessive vegetative growth. The normal growth appearance during the squaring stage is a thick and sturdy stem, compact internodes on the main stem, and red stem accounting for 60%; plant width greater than height; the growing tip sunken and plump, strongly heliotropic; leaves moderate in size and oily green in color; fruiting branches robust, with large and numerous squares; on average, about one new fruiting branch every three days. The daily increment of the main stem increases from 0.3 cm at squaring to 1-1.5 cm, reaching 2-2.5 cm at the peak squaring stage. At flowering, plant height is 50-55 cm, with about 10 fruiting branches and more than 20 flower buds.

Rational management of fertilizer and water

1. Steady fertilization. The fertilizer requirement of cotton at the squaring stage is noticeably greater than at the seedling stage, and fertilization should be flexibly controlled according to plant growth, soil fertility, weather conditions and so on. For cotton fields with good soil fertility, sufficient base fertilizer and vigorous growth, it is not suitable to apply quick-acting nitrogen fertilizer as a top dressing; an appropriate amount of cake fertilizer and potassium fertilizer may be applied. Apply 25-30 kg of cake fertilizer and 10-15 kg of potassium fertilizer per mu. For cotton fields of medium fertility with sufficient base fertilizer and fairly good seedling growth, 10-15 kg of nitrogen-phosphorus-potassium compound fertilizer may be applied per mu; for cotton fields with poor soil fertility, insufficient base fertilizer and poor seedling growth, an appropriate top dressing of quick-acting nitrogen fertilizer should be applied, generally 5-7.5 kg of urea per mu at the early squaring stage. The top dressing should preferably be placed about 30 cm from the cotton plants, applied deeply and compacted, which can both fully release the fertilizer effect and prevent fertilizer damage.

2. Skillful watering. During the squaring stage, cotton requires the soil moisture in the 10-30 cm layer to be maintained at 60-70% of field maximum water-holding capacity, and watering should be carried out immediately to prevent drought when it drops to 50%. To ensure steady growth of cotton seedlings, flood irrigation must be avoided; instead, furrow irrigation in alternate rows should be used, with 30 cubic meters of water per mu. After watering during the squaring stage, deep intertillage and loosening of the soil must be carried out promptly to break up crusting, promote downward root growth, and enhance the ability to resist drought and tolerate waterlogging later.