Comprehensive growth regulation technology for high-density cultivation of cotton variety 81-3

The 81-3 variety has the characteristics of a high boll-setting rate per plant, strong boll retention, disease resistance, high yield and good quality, and is currently the main variety planted by our regiment. At the same time, the 81-3 variety also has the characteristics of weak growth vigour at the seedling stage, gradually strengthening growth vigour at the bud stage, strong growth vigour at the flowering stage, no premature senescence in the late stage, and a rather long growth period. To obtain large-area abundant and high yields under high-density cultivation conditions, it is necessary, on the premise of scientifically and rationally managing water and fertiliser, to coordinate the relationship between vegetative growth and reproductive growth of cotton, and to master the comprehensive growth regulation technology for high-density, high-yield cultivation of 81-3.

I. Early-stage growth regulation (seedling stage to early bud stage)

1. From emergence to the two-true-leaf stage, cotton needs to solve two problems. (1) Cotton fields sown early before April 20 are prone to late-spring cold spells in late spring and early summer, causing newly emerged cotton seedlings that encounter rain to become stunted seedlings with delayed or late development. If the soil moisture in the cotton field is too high, it can also easily cause the death of cotton seedlings. (2) After the emergence of late-sown cotton after April 20, because temperature and light are relatively good, leggy seedlings are very easily formed. Therefore, to prevent the appearance of stunted seedlings and leggy seedlings, when the cotton seedlings in the field have all emerged and the two cotyledons have flattened out up to the 4-true-leaf stage, for gravel gobi land or cotton fields where the soil was too wet during pre-sowing preparation and the cotton seedlings are rather weak in growth, carry out 2 to 3 growth regulation treatments. The 1st, after full emergence when the two cotyledons have flattened out, apply 50 g monopotassium phosphate + 50 g urea per 667 sq m to promote seedling growth; the 2nd, at the 2-leaf 1-heart stage of the cotton seedlings, apply 0.5 to 0.8 g mepiquat chloride per 667 sq m for light regulation to promote steady seedling growth; the 3rd, at the 4-leaf 1-heart stage of the cotton seedlings, apply 1 to 1.5 g mepiquat chloride per 667 sq m for regulation, to promote steady and vigorous seedling development and lower the height of the first fruiting branch node of the cotton. For cotton seedlings on sandy loam and loam soil, adopt a mainly controlling approach and carry out 2 to 3 mepiquat chloride growth regulation treatments. The 1st, after full emergence when the two cotyledons have flattened out, apply 0.3 to 0.5 g mepiquat chloride per 667 sq m for growth regulation to promote seedling root development; the 2nd, at the 2-leaf 1-heart stage of the cotton seedlings, apply 0.6 to 1 g mepiquat chloride per 667 sq m for growth regulation to promote steady seedling growth; the 3rd, at the 4-leaf 1-heart stage of the cotton seedlings, apply 1 to 1.5 g mepiquat chloride per 667 sq m for regulation, to promote steady and vigorous seedling development and lower the height of the first fruiting branch node of the cotton.

2. When the cotton seedlings have grown to 5 to 6 true leaves, the growth vigour of the cotton plants gradually strengthens. At this stage, in order to ensure a well-developed root system and leaf emergence rate of the cotton seedlings and to make the cotton seedlings grow steadily, carry out the 4th mepiquat chloride growth regulation treatment, applying 2 g mepiquat chloride per 667 sq m. To ensure that growth regulation is carried out in place, all 4 growth regulation treatments from the seedling stage to the early bud stage are mechanical growth regulation treatments, with each growth regulation treatment spaced 7 to 10 days apart.

II. Mid-stage growth regulation (bud stage to early flowering stage)

From the bud stage to the early flowering stage, in order to ensure the transition from vegetative growth to reproductive growth, comprehensive regulation is mainly adopted through measures such as fertiliser and water regulation, mepiquat chloride growth regulation and cotton topping and pruning. The daily growth increment indicators of cotton plants at this stage are: the daily growth increment of cotton plants is less than 1 cm before the first drip irrigation and less than 1.5 cm after the first drip irrigation, and this must be maintained until cotton topping. When the first cotton flower opens, plant height should be controlled at about 40 cm, with medium-sized leaves. At this stage, carry out 2 to 3 mepiquat chloride growth regulation treatments. The 1st, about June 10, 1 to 2 days before the first drip irrigation: for gravel gobi land or cotton fields with rather serious localised drought, apply 0.5 to 1 g mepiquat chloride per 667 sq m for light regulation; for cotton fields on sandy loam and loam soil where the cotton seedlings are growing normally, 3 days before the first drip irrigation, apply 1.5 g mepiquat chloride per 667 sq m for mechanical growth regulation. The 2nd, when cotton enters the full bud stage to early flowering stage; at this time the purpose of growth regulation is mainly to prevent hollowing, ease the contradiction between individual plants and the population, promote the transport of cotton nutrients to buds and bolls, and improve the structure of buds and bolls. Growth regulation at the early flowering stage is generally carried out before the 2nd irrigation, that is, June 18 to 20, generally applying 1.5 to 2 g mepiquat chloride per 667 sq m. The 3rd growth regulation treatment is before the 3rd irrigation before cotton topping, from June 30 to July 2; this growth regulation has the effect of preventing hollowing and excessive growth caused by not being able to top in time after water enters the cotton field, and should be lightly regulated as appropriate according to seedling growth, with a mepiquat chloride dosage of 1 to 1.5 g per 667 sq m.

III. Late-stage growth regulation (flower and boll stage)

1. The 81-3 variety has the characteristics of strong growth vigour at the flower and boll stage, no premature senescence in the late stage, and an inverted-tower plant shape. In order to prevent the top 3 fruiting branches of the cotton plant from elongating too quickly after topping, causing excessive growth of the cotton plant to shade and block light and resulting in flower and boll shedding, carry out timely mepiquat chloride growth regulation for top sealing after topping, with two top-sealing treatments giving good results. The 1st mepiquat chloride growth regulation top sealing is carried out on the 3rd day after topping is completed, applying 4 to 6 g mepiquat chloride per 667 sq m; the 3rd is within the 7th to 8th day after topping is completed, applying another 4 to 6 g mepiquat chloride per 667 sq m. After topping, two points should be noted in growth regulation: first, the timing should not be too late; generally the two mepiquat chloride growth regulation top-sealing treatments are completed within 8 to 10 days; second, the mepiquat chloride dosage must be accurate.

2. The 81-3 variety has the characteristics of many bolls per plant and a high boll-setting rate. In early to mid-August, spray 150 g monopotassium phosphate + 100 g urea + 2 g brassin per 667 sq m on the leaves, for 2 to 3 consecutive applications, to nourish the roots and protect the leaves and increase boll weight.

In the comprehensive growth regulation technology for high-density cultivation of the 81-3 variety, the early stage should focus on growth regulation, while the middle and late stages should focus on fertiliser and water regulation, implementing early and steady development of fertiliser and seedlings, steady growth of plant development in the middle stage, slow growth in the late stage, and combining promotion and control, so that cotton grows steadily throughout the entire growth period, with suitable plant height, good boll setting in the middle and lower parts, no empty top, many bolls set per cotton plant in early to mid-August, no excessive growth and no premature senescence, achieving the goal of stable and high yield.