Cotton plants produce flowers that eventually give way to spherical seed pods called cotton bolls. These burst open as the weather warms, revealing moist fibers inside.
To harvest the bolls, machines use rotating spindles to twist the cotton out of the opened boll and transfer it into a basket. A second machine, the cotton stripper, utilizes rollers with brushes and bats to pull the cotton out of the plant.
Defoliation is a critical step in the preparation of cotton for harvest. It reduces the main sources of stains and trash on the cotton plant and can increase harvest efficiency, improve lint quality, and prevent boll rot. Defoliation also allows a crop to more effectively utilize soil moisture and nutrients.
Cotton producers should carefully consider crop maturity, field conditions, and environmental factors when making defoliation decisions. Defoliating a cotton crop too early or too late can impact yield potential, fiber quality, and overall crop health.
When it comes to defoliation timing, there is as much art as science involved. One popular rule of thumb is to defoliate when 60%-75% of a field’s bolls are open. This strategy works well for crops with uniform fruiting initiation and high fruit retention. However, it can be tricky with uneven fruit distribution. If insect pressure or stress has resulted in a high percentage of immature fruit, defoliating at this stage would likely disrupt fiber development and decrease yield and micronaire.
Another way to determine whether a crop is ready for defoliation is to use the nodes above the cracked bolls (NACB) method. This approach finds the highest cracked boll on the plant and counts how many nodes are above it that have harvestable buds. Research has shown that a cotton crop can be safely defoliated when four or more nodes above the highest cracked boll are ready to harvest.
Various harvest aid products are available to help with defoliation and synchronization of boll opening. These include regrowth retardants and desiccants that help inhibit regrowth, as well as bolt openers and boll opening compounds that accelerate the process of maturing buds. Boll openers are often recommended to be tank-mixed with defoliants and are most effective in warm weather.
Regardless of which defoliation method is used, the goal is to be sure that all harvestable bolls are opened and mature before applying a defoliant. A good test for this is to slice a mature boll with a knife. A boll is considered to be fully mature and ready for harvest aid applications when it cannot be sliced without “stringing” the lint.
The harvesting process involves removing all of the open bolls and seed cotton from the plant. It is done by either picking the bolls by hand or using mechanical harvesting equipment. Picking by hand is time-consuming but preserves the fiber characteristics of cotton better than machine picking. It can also produce back aches and burrs in the hands of laborers and is not very efficient.
Using machines like pickers and strippers to harvest cotton reduces the amount of waste from the harvested crop, which improves grades, yield, and profitability. This type of harvesting requires the use of defoliants to promote quick leaf drop and boll opening, and the plants need to be fully matured for the machine to function effectively.
As technology advanced, hybrid plant breeders were able to produce varieties that grew higher off the ground, making it easier for the machinery to reach the bolls. Herbicides were also developed that would defoliate the plants, encouraging them to drop their leaves before the harvester came through, producing a cleaner, more uniform crop.
The timing of when a crop is ready to be harvested depends on the weather and can affect the quality of the cotton produced. A late crop may experience moisture stress from too much rain, which reduces the boll opening rate and can cause poor fiber quality. The ideal weather conditions for a good harvest include clear sunshine and a high soil moisture level.
While defoliants can speed up the process of the cotton crop maturing and boll opening, it is important to remember that they do not work well on wet, saturated, or soggy soils. This can cause the chemicals to move through the plant and not defoliate or open the bolls.
Several different tillage techniques are used in the field to prepare crops for harvesting, including conventional tillage, conservation tillage, and no-till farming. Conventional tillage uses a plow to till the soil, allowing it to break up and incorporate any residue from previous crops. This practice has been found to lead to a decreased use of herbicides, which is beneficial for the environment and reduces costs for farmers. However, this tillage technique can lead to compaction and crusting of the soil, which can limit water absorption, resulting in erosion and runoff.
A major hurdle in the cotton harvesting process is separating the seed cotton from the rest of the plant (the leaves, stalk, and bolls). In order to minimize this waste, growers use different types of equipment to harvest cotton. These machines are called pickers or strippers. They are typically based on an electrical, pneumatic, or mechanical system. These systems pluck/pick open bolls with spindles, fingers, or prongs while causing minimal material damage to the foliage and unopened bolls.
When choosing the proper harvesting machine to utilize in a given field, farmers look for equipment that will collect as much of the lint and cottonseed as possible. This will reduce the amount of trash that is returned to the gin. The goal is to achieve a high yield of clean, quality cotton that can be used to make bed sheets, soft towels, and other clothing.
In the late 1800s and early 1900s, critical advances were made in cotton harvesting technology. Breeders developed hybrid plants that produced bolls higher off the ground and ripened uniformly, which made them easier for combine harvesters to pick. Chemicals were also developed to defoliate cotton plants, allowing them to drop their leaves before the harvester passed through the field. This significantly reduced the amount of debris that was left behind and helped produce better-quality cotton.
At the same time, cotton harvesters were also improved. The most successful prototype was a spindle-style mechanism. A series of moistened spindles, similar to those in a spinning wheel, would rotate at high speed, and when they encountered an open boll, the cotton fibers wrapped around the spindles and were pulled by a doffer into a basket for transport to the gin.
While this is an effective way to harvest cotton, it does not always produce the most efficient results. As a result, it is best to wait until 60 percent of the bolls in a field are fully opened and ready to be harvested. Visual inspection and a boll mapping technique will help determine when this benchmark has been achieved.
Cotton is harvested by a machine called a cotton picker or a person who picks the ripe cotton fiber from the plant. It takes approximately 160 days from planting for a cotton crop to be ready to harvest. The ripe cotton bolls will burst open, exposing the fluffy white fiber inside. This usually happens around July in South Texas and September through November in the northern part of the state.
Farmers can harvest the cotton by hand, using a cotton picker machine, or by air with specialized airplanes known as crop dusters. Cotton growers also use chemicals known as defoliants and boll openers to maximize yield and harvest quality. These chemicals encourage the plants to unnaturally shed their leaves, eliminating the main source of stains and trash in harvested cotton. They also help dry the cotton enough for mechanical harvesting and stimulate boll opening and maturation.
Once the ripe cotton is ready to be picked, it’s transferred from the boll buggy into modules that contain eight to twelve bales of fiber. These modules are then sent to a cotton gin for processing and preparation before the lint is shipped out to textile mills and purification manufacturers.
A typical cotton plant consists of one central stalk with multiple branches, each bearing several buds that produce fruit. The flowers produced by the branches have small seeds inside that will mature to become cotton bolls containing fluffy white fiber. Cotton producers must carefully monitor the growth of their crops and make decisions about when to harvest.
The most popular method of cotton harvesting involves using a machine known as a cotton picker. These machines can be pneumatic, electrical, or stripping in nature and can be configured with various nozzles that allow the operator to select specific parts of the plant to harvest. The pickers can remove a portion of the plant’s stem, roots, and leaves along with the ripe bolls and unopened bolls.
A pneumatic cotton picker uses suction to separate and remove the ripe cotton from the plant without causing any material damage to the remainder of the plant. The electric cotton picker is a bit more sophisticated and takes advantage of the natural static electricity present in the fiber to draw it toward revolving spindles on the cotton picker machine. However, this complex technology requires a great deal of engineering and maintenance.