How to carry out field management during the cotton squaring stage?

I. Growth characteristics of the squaring stage

The cotton squaring stage refers to the period from squaring to flowering. It generally begins from late May to early June and lasts 25-30 days. About 40 days after cotton emergence, when a triangular young bud up to 3 mm wide appears at the first fruiting node of the first fruiting branch on the cotton plant, this is called squaring.

The appearance of the bud marks the transition from predominantly vegetative growth to a period in which vegetative growth and reproductive growth proceed together, but vegetative growth still predominates, mainly expanding the vegetative body. During this period, dry matter accumulation in the cotton plant continuously increases, and carbon-nitrogen metabolism shifts from being dominated by nitrogen metabolism at the seedling stage to being centered on carbon metabolism. If fertilizer and water are insufficient, vegetative growth is inhibited, carbon metabolism is impeded, and the vegetative body is too small, which easily causes premature senescence. If nitrogen supply is excessive, too much sugar is used to synthesize protein, causing excessive vegetative growth and spindling, field closure, and poor ventilation in the lower part, resulting in massive shedding of buds in the middle and lower parts. After bud shedding, the nutrients originally transported to the buds on the middle and lower fruiting branches are transported upward in large amounts, further promoting runaway growth of the cotton plant and forming a vicious cycle, failing to retain early buds, failing to set early bolls, and forming the so-called "tall, big, empty".

The plant appearance of cotton at the squaring stage is: compact plant type, thick and strong stem, close nodes, fruiting branches extending horizontally in all directions with a relatively large angle of insertion, evenly distributed internodes, moderate leaf size, and many and large buds. If the plant type is loose, the stem is thick with sparse nodes, the fruiting branches grow upward with a small angle of insertion, the fruiting branches are slender and the fruiting nodes are long, the leaves are hypertrophic, and the buds are few and small, it is a vigorous seedling. If the plant type is short and small, the stem is thin and the plant is lean, and the leaves are small and the buds are few, it is a weak seedling.

II. Field management

The management task at the squaring stage is to focus on fertilizer and water, combined with intertillage, pruning, pest and disease control, and chemical regulation techniques, to coordinate the relationship between vegetative growth and reproductive growth, achieving strong but not spindling, steady but not declining, and on the basis of strong seedlings and early development, achieving a steady increase in flower buds. Irrigated and fertile cotton fields should mainly be controlled, while dry and poor fields should mainly be promoted.

(I) Fertilizer and water application

Fertilization at the squaring stage must both meet the needs of strong plants and prevent excessive growth caused by too much fertilizer, achieving steady and skillful application.

In northern cotton regions, for early-maturing or poor cotton fields, fertilization at the squaring stage has a good effect; for cotton fields with sufficient base fertilizer and high density, appropriate control should be exercised at the squaring stage, generally no quick-acting nitrogen fertilizer is applied, and a key fertilization can be applied at the early flowering stage; for cotton fields with medium fertility, a single topdressing can be applied at the full squaring stage or early flowering stage, or two topdressings can be applied at the early squaring stage and early flowering stage; for high-yield cotton fields, on the premise of sufficient base fertilizer, adding organic fertilizer at the squaring stage has a great effect on increasing yield.

Cotton requires a relatively large amount of water at the squaring stage. In northern cotton regions, rainfall at the squaring stage is relatively low, and evaporation is severe, so timely and appropriate irrigation plays an important role in increasing yield. In general cotton fields, to alleviate the conflict between the concentrated farm work of the "three summer" period and water use for summer planting, irrigation is often carried out before wheat harvest; in high-yield cotton fields, to prevent excessive growth, the first irrigation is often delayed, which can promote deeper root growth and help enhance the drought resistance of the cotton plant, but the irrigation time should be combined with local climatic conditions.

(II) Intertillage and earthing up

Intertillage at the squaring stage can play a role in drought resistance and moisture conservation, eliminating weeds, promoting deeper root growth, and controlling excessive growth. At the squaring stage, 3-4 intertillages are required, following the principle of "hoe after rain, hoe after irrigation, hoe when there are weeds." Intertillage should be deepened progressively, and for vigorously growing cotton fields, deep hoeing should be carried out, reaching a depth of 10-14 cm. Before row closure, intertillage should be combined with earthing up, carried out in stages, and completed before the rainy season arrives. The suitable height for earthing up is about 17 cm. The benefits of earthing up are: it conserves moisture in light drought, facilitates furrow irrigation in severe drought; it facilitates drainage in waterlogging, prevents cotton plant lodging, and can also increase soil temperature, promote root development, and inhibit weed growth, etc.

(III) Pruning

1. Removing leaf branches. After the cotton plant has squared and fruiting branches and leaf branches can be clearly distinguished, promptly remove the leaf branches below the first fruiting branch. Whether to retain leaf branches and how many to retain depends on the density of retained seedlings. For low density or dry and poor land, pruning may be omitted entirely, and when leaf branches have grown 1-2 fruiting branches, topping can be carried out promptly; for moderately dense and steadily growing cotton fields, 1-2 leaf branches may be retained, and topping carried out when the leaf branches have 1-2 fruiting branches; for cotton fields with a tendency to vigorous growth, all leaf branches may be removed. Removing leaf branches should be handled flexibly and not forced uniformly. At field edges and in areas with missing seedlings or broken rows, 1-2 leaf branches may be retained to make use of the space to set more bolls.

2. Removing superfluous buds. In the leaf axils of the main stem and fruiting branches, buds often appear that only consume nutrients and also affect ventilation and light penetration; these are called superfluous buds and should be removed promptly. When removing superfluous buds, the principle is "buds not longer than a finger, branches not longer than a cun, remove them small and remove them early."

3. Removing early buds. For medium-early maturing varieties and cotton fields sown too early, after removing the early buds, by using the cotton plant's own ability to regulate and compensate boll setting, the following effects can be achieved: First, reducing pre-dog-days bolls can correspondingly reduce rotten bolls and hard locks, and solve and alleviate premature senescence. Second, increasing dog-days bolls and early autumn bolls, so that the mass flowering period coincides with the optimal boll-setting period. Third, increasing the proportion of bolls set on inner and middle fruiting branches, increasing the income from pre-frost cotton. Fourth, promoting root development and root vigor, extending the functional period of leaves, and enabling healthy growth of the cotton plant.

There are many methods for removing early buds, generally carried out when the cotton plant reaches 6-7 fruiting branches. Removing all flower buds from the basal 2-3 fruiting branches has the best effect. This measure is suitable for cotton fields with medium or higher fertility, and flower and boll fertilizer should be increased.

(IV) Pest and disease control

1. Diseases. The squaring stage is the peak period for cotton Fusarium wilt. There are currently no very effective control measures and chemicals for this disease. Only through agricultural measures can cotton seedlings be promoted to have strong roots and strong plants, increasing resistance and preventing pathogen infection. Such as deep plowing of the land, increasing the application of organic fertilizer and potassium fertilizer, etc.

2. Insect pests. With the planting of insect-resistant cotton, mirids have risen to become the main pest. At this stage, it is necessary to closely monitor changes in insect conditions in cotton fields and take the initiative. If black spots or brown spots are found on tender leaves, pesticides should be sprayed promptly for control, striving to prevent female adults from laying eggs and reproducing on cotton plants.

Pesticides such as kelinychun (produced in Tianjin), endosulfan, leqiben, phoxim, and malathion currently all have good control effects on mirids, and organophosphorus pesticides combined with pyrethroid pesticides have even better effects.

(V) Chemical regulation as appropriate

For vigorously growing cotton fields, carry out 1-2 light chemical regulations at the squaring stage, spraying 0.3-0.5 g of mepiquat chloride per mu each time, which can maintain steady growth of the aboveground part, promote robust root growth, and help strengthen plants and prevent disease.