When is the cotton flowering and boll stage? How should water and fertilizer management be controlled? How should fertilizer be applied?

After cotton topping, it enters the flowering and boll stage. This period is the key period for cotton yield formation and also the peak period of water and fertilizer demand. During this period, field management of cotton is crucial. So when is the cotton flowering and boll stage? How should water and fertilizer management be controlled?

When is the cotton flowering and boll stage?

The period from the beginning of flowering to the maturity, cracking and fluffing of cotton bolls is called the flowering and boll stage, generally from early July to late August. This period is when cotton transitions from simultaneous vegetative growth and reproductive growth to being dominated by reproductive growth. It is not only growing roots, stems, branches and leaves, but also budding, flowering and setting bolls. It is the most vigorous period of growth and development in the entire life of cotton, the peak period of fertilizer and water demand, and the key period for yield and quality formation.

From flowering——to boll opening, nitrogen uptake accounts for 60%, phosphorus 65%, and potassium 62%. Therefore, timely and appropriate topdressing promotes boll formation, prevents premature senescence, increases the number of bolls set at all three positions, reduces shedding, increases boll weight and improves lint percentage.

Notes on water, fertilizer and chemical control in July

(1) Roles of nitrogen, phosphorus, potassium and trace element fertilizers:

In simple terms, nitrogen fertilizer determines how tall and large the plant grows, phosphorus fertilizer determines how robust the plant grows, potassium fertilizer determines resistance and quality, and among trace elements, zinc fertilizer participates in the synthesis of auxin, boron fertilizer promotes the growth and development of reproductive organs, etc.

(2) Utilization rates of nitrogen, phosphorus and potassium:

Nitrogen fertilizer utilization rate 30-40%, phosphorus fertilizer utilization rate 15-25%, potassium fertilizer utilization rate 30-50%

(3) Principles of cotton topping:

The principles of cotton topping are to top the weak first and the strong later, to top the dense first and the sparse later, and to top the vigorous first and the sturdy later. Many farmers do not understand why the weak should be topped before the strong. The reason weak cotton seedlings are weak is that their growth and development process is slower. At the current time, the shift from vegetative growth to reproductive growth is needed, but weak seedlings transform more slowly. If topping is too late, after the weak seedlings perk up they will wash away the flower buds to maintain the nutrients needed for vegetative growth. Later, after the bolls reach the top, there will basically be no bolls in the middle, and the top bolls will mature relatively late. If the frost period comes early, they will basically all be watery bolls. In this situation, vegetative growth must be blocked as early as possible, fewer fruit branch nodes should be retained, and the basic yield should be ensured.

(4) Principles of cotton fertilization

Combine organic and inorganic, combine major elements and trace elements, and combine fertilizer application based on yield with soil testing and formulated fertilization; fertilization methods: apply sufficient base fertilizer, lightly apply seedling fertilizer, steadily apply squaring fertilizer, heavily apply flowering and boll fertilizer, and supplement with top-covering fertilizer.

Heavy application of flowering and boll fertilizer:

In fertilization, cotton plants should be controlled so they do not grow excessively. For cotton fields with high fertility and vigorous plant growth, topdressing can be delayed. For example, after topping, 3-5 days later use 5-8 grams of mepiquat chloride for one heavy control, then apply 2-3 kg urea, 3-5 kg phosphorus fertilizer, and 1-2 kg potassium fertilizer by drip irrigation. Heavy water and fertilizer must be postponed until the full flowering stage when the lower part of the plant has 1-2 large bolls; for cotton fields with low fertility and weak growth, flowering and boll fertilizer should be applied early and heavily at the initial flowering stage. Generally, it starts in early July combined with drip irrigation, and per mu the principle of “one irrigation with one fertilization, water with fertilizer, fertilizer determined by water, water regulated by fertilizer” is followed. These fertilizers are applied in split topdressings. After topdressing, irrigation and chemical regulation should also be carried out in a timely manner according to weather and cotton growth conditions. Foliar fertilization can be appropriately combined, generally using a 1%-1.5% monopotassium phosphate mixed solution sprayed on the leaves 1-2 times, with an interval of 7 days each time.

The time for heavy application of flowering and boll fertilizer after cotton topping should be 5-7 days after the second chemical control. If cotton has not been locked at the top by the second heavy control and heavy water and fertilizer enter, it is very easy to wash the top open. When small fuzz appears at the top, the top will consume a large amount of nutrients, and under such circumstances the top-covering bolls basically cannot set.

Supplemental application of top-covering fertilizer:

 Top-covering fertilizer has the effects of preventing premature senescence, preventing shedding, setting more bolls and increasing boll weight. Whether top-covering fertilizer should be topdressed depends on soil fertility and cotton plant growth. For late-maturing cotton fields with sufficient fertility, good staying power and vigorous plant growth, as well as saline-alkali land and clay land, top-covering fertilizer should be applied sparingly or not at all to prevent excessive vegetative growth and late maturity; for sandy land with weak cotton plant growth and cotton fields where plants show a trend of premature senescence, it should be applied early and more heavily.

(5) Cotton fertilization methods:

From flowering to boll opening, nitrogen uptake accounts for 60%, phosphorus 65%, and potassium 62%. At this stage, these nutrients should be applied gradually according to “less—more—less”. For vigorously growing cotton fields and cotton fields in southern Xinjiang that are topped relatively late, water and fertilizer timing differs from northern Xinjiang. For example, if topping in southern Xinjiang is during July 10-15, the high water and fertilizer schedule is as follows:

For example, for an ordinary plot (according to one irrigation every 8-10 days): drip irrigation situation for cotton fields topped on July 10

On July 15, drip 2-4 kg urea, 4-5 kg phosphorus fertilizer (can be omitted if base fertilizer is sufficient), 2-3 kg potassium fertilizer; on July 13, control with 5-8 grams mepiquat chloride.

On July 24, drip 3-6 kg urea, 5-6 kg phosphorus fertilizer, 3 kg potassium fertilizer. On July 20, use mepiquat chloride to seal the top growing point, with a per-mu dosage of 10-15 grams of mepiquat chloride according to cotton conditions.

On August 3, drip 6-8 kg urea, 4-5 kg phosphorus fertilizer, 3-4 kg potassium fertilizer.

On August 12, drip 6-8 kg urea, 3-5 kg phosphorus fertilizer, 4-5 kg potassium fertilizer.

On August 21, drip 5-6 kg urea, 2-3 kg phosphorus fertilizer, 4-5 kg potassium fertilizer.

On September 1, drip 1-2 kg urea, 1 kg phosphorus fertilizer, 1 kg potassium fertilizer (for plots without premature senescence, no fertilizer is carried in this irrigation). If irrigating every 10 days, appropriately increase the dosage each time, and so on.

For high-fertility plots, delay fertilization time and appropriately reduce the amount; for low-fertility land, appropriately increase the amount.

(6) Application of micro-fertilizers:

Cotton is relatively sensitive to boron. Applying boron fertilizer can prevent the “budding but not flowering” disorder in cotton, increase the boll-setting rate and promote large bolls. Whenever the available boron content in the soil is below 0.5 mg/kg, boron fertilizer should be added and sprayed on the leaves, generally using 100-200 grams of 20.5% granular boron solution per mu. Use once each at the full squaring stage, initial flowering and full flowering stage.

(7) Precautions:

1. Do not mix phosphorus fertilizer with zinc fertilizer (except chelated zinc) to avoid antagonism that reduces fertilizer efficiency.

2. Combine fertilization with regulation (for the two chemical controls, respectively use 5-8 grams of mepiquat chloride when the top fruit branches extend 3-5 cm, and after 7-10 days use 10-15 grams of mepiquat chloride. This year, due to restricted weather from earlier disasters, after temperatures rose later the cotton grew vigorously. During the second chemical control, the fertilization amount should not be too large, and the second chemical control must thoroughly control the top), and combine water and fertilizer with chemical control to avoid excessive growth.

3. In cotton fields with soil salinization, potassium chloride should not be applied, so as to avoid worsening soil salinization.

Factors likely to cause flower and boll shedding in July

1. In the earlier period, cotton did not grow due to disastrous weather. Because irrigation was too early, the root system generally penetrated relatively shallowly. During the fertilizer-demand period, the root system's ability to absorb fertilizer was limited, causing flower and bud shedding due to insufficient nutrient supply.

2. Field canopy closure affected cotton functional leaves, causing serious bud and boll shedding. In the earlier period this year, cotton did not grow, and many farmers used some hormone-type foliar fertilizers to promote seedlings, which made the leaves grow very large, causing the functional leaves to be unable to photosynthesize well and provide nutrients to the cotton bolls.

3. The threat of pests and diseases. Due to the disastrous weather in May, cotton was relatively tender, making pests and diseases occur more seriously, such as aphids and Fusarium wilt, causing a large number of buds to shed.

4. Higher density affected bud and boll development. In high-density cotton fields, field canopy closure occurred earlier, causing many small buds and bud and boll shedding.

5. Unreasonable water and fertilizer. Because cotton seedlings grew weakly in the earlier period, many farmers promoted seedlings early and applied more urea, making vegetative growth excessive and causing reproductive growth to stop or proceed slowly, also resulting in small buds or slow budding.

To prevent flower and bud shedding, we must start with water and fertilizer and with mepiquat chloride chemical control after topping.

1) The timing of fertilization must be well controlled. For example, before the red flower reaches the top, definitely do not flush the field with heavy water and fertilizer, as this will make it difficult for buds in the middle, upper and outer parts to set. Too much water and fertilizer can easily cause the cotton field to shift again from being dominated by reproductive growth to being dominated by vegetative growth.

2) The second chemical control must be in place. The second chemical control, especially the second top-locking, must lock the top in one application. If it is washed open by leaf buds, nutrients will be consumed and the top-covering bolls will not set steadily, so that the top-covering bolls cannot set.

3) Heavy water and fertilizer must wait until the top is locked and 3-4 fruit branches in the middle and lower parts have set bolls before being carried out.