Am. Soc. Agronomy 11(7): 299-303 (Oct. 1919)
EXPERIMENTS IN SPACING COTTON.1
O. F. COOK
|1 Contribution from the Bureau of Plant Industry, United States Department of Agriculture, Washington, D. C. Received for publication May 5, 1919.|
Knowledge of the structure and habits of a plant is essential to a full understanding of cultural requirements. It is not sufficient to perform experiments, or to give directions. Established opinions and customs are not changed until the underlying facts and relations are brought clearly before the mind. A theory may become dominant, like that of wide spacing of cotton, even without facts to support it. Belief governs action in agriculture no less than in other fields of human effort. New facts or principles are not fully applied until they are generally and thoroly understood, and the previous opinions are seen to have been defective.
General reasoning that may be applicable to other crops is distinctly out of place with cotton, because the plant has habits of its own. There is no direct or regular relation between the size of cotton plants and the yield of lint and seed, but very often a contrary or inverse relation, smaller harvests from larger plants. The key to this paradox is that the main stalk of the cotton plant produces two distinct kinds of branches, one kind able to bear an early crop of bolls, the other not. If growth is too luxuriant at first vegetative branches are developed at the expense of fruiting branches.
Rank growth of young cotton plants also leads to blasting and shedding of floral buds or young bolls, and even to general abortion of the early fruiting branches, in cases where young plants that have behaved normally in the first weeks pass into a very luxuriant condition, in warmer weather. The physiological state of plants making rapid vegetative growth not only is unfavorable to the setting of fruit but apparently involves injury and death of the fruiting parts, even when other unfavorable conditions are not encountered.
Chances of an early crop are much better with plants of moderate, restricted growth and only a central or main stalk, than with the large plants that develop numerous vegetative branches or side stalks. Plants that produce only a single stalk not only are in a better physiological state for producing and retaining floral buds and young bolls early in the season, but cultural conditions in single-stalk fields are also more favorable for bringing the early bolls to maturity. Injurious crowding is avoided by suppressing the side stalks, altho the plants are more numerous and stand closer together in the rows. The rather narrow, upright form of the single-stalk plants permits the space between the rows to remain open, so that the lower fruiting branches continue to be reached by the light and heat of the sun. When the plants grow large and have strong vegetative branches that fill the space between the rows, the lower fruiting branches are thrown into deep shade and most of the early bolls are aborted.
|2 For more detailed accounts of structural and cultural features see publications of the U. S. Department of Agriculture, especially the following: Dimorphic Branches of Tropical Crop Plants, Bur. Plant Indus. Bul. 198; Arrangement of Parts in the Cotton Plant, Bur. Plant Indus. Bul. 222; the Branching Habits of Egyptian Cotton, Bur. Plant Indus. Bul. 249; Morphology of Cotton Branches, Bur. Plant Indus. Cir. 109; A New System of Cotton Culture, Bur. Plant Indus. Cir. 115; Abortion of Fruiting Branches in Cotton, Bur. Plant Indus. Cir. 118; A New System of Cotton Culture and Its Application, Farmers' Bulletin 601; Single-Stalk Cotton Culture, Bur. Plant Indus. Doc. 1130; Brachysm a Hereditary Deformity of Cotton and Other Plants, Jour. Agr. Research, 3: 387; Single-Stalk Cotton Culture at San Antonio, Texas, Dept. Bul. 279; Experiments with Single-Stalk Cotton Culture in Louisiana, Arkansas and North Carolina, Dept. Bul. 526.|
Vegetative branches not so large or so numerous as to interfere directly with the development of early bolls may still be injurious indirectly. Overgrown plants are more likely to be checked by drouth, which is another cause of blasting and shedding of buds or young bolls. In some experiments large spreading plants were conspicuously wilted in the middle of the day, while small plants in adjacent rows remained turgid. Such differences of behavior explain the cultural superiority of single-stalk plants, and the advantage of suppressing or avoiding the development of the vegetative branches. Usually this can be accomplished by the simple expedient of leaving the plants closer together in the rows, and thinning them later than was formerly considered advisable. The system of controlling the vegetative branches has been described as single-stalk cotton culture.2
The experiments that have been made under a very wide range of conditions in different parts of the cotton belt leave no doubt that the principle of control of branching can be used to general advantage, but no uniform directions can be given that would insure the best results under all conditions. To expect this would be as reasonable as prescribing universal methods for other farm operations. As already explained, the single-stalk system is flexible and readily adapted to circumstances. Bad weather, lack of labor or other obstacles may interfere with thinning at an ideal time, but whenever the work is done the principle of control needs to be taken into account.
Practical familiarity can be gained by simple comparisons of 12-inch and 6-inch spacings in alternate blocks of 4 or 5 rows, with both spacings thinned at the same time, preferably when the plants are from 6 to 10 inches tall. The number and size of the vegetative branches developed in the 12-inch spacing will serve as a measure of luxuriance for the local conditions, while the 6-inch rows will show more restriction and control. If vegetative branches are not developed in the 12-inch spacing, it will be evident that thinning was deferred much longer than was necessary to suppress vegetative branches in the 6-inch rows, and that earlier thinning might have increased the yields of these rows. It is only in extreme conditions, as on plants forced into rapid growth after being checked severely by cold or dry weather, that large vegetative branches develop in 6-inch spacings, unless the stands are irregular. Loss of the terminal bud often results in the development of several vegetative branches, but if thinning is not done too early the injured plants are easily recognized and removed.
Thick stands require earlier thinning, while open stands sometimes yield better without thinning. Cotton of moderate growth may be thinned earlier than rank-growing cotton, but very early thinning, before the plants are 5 or 6 inches high, exposes the seedlings prematurely, and often injures the crop by reducing the stand or by increasing the number of plants crippled by leafcut or injured by insects. Late planted cotton usually needs to he left closer to the rows and thinned at a more advanced stage of growth than early plantings, often not until the plants are 10 or 12 inches high, or even i or 18 inches, depending upon the stand and other conditions of growth. Another general relation is that of time of thinning to the spacing that should be used. If the spacing is to be close there is less need to defer thinning, but if thinning is much deferred it becomes more necessary to use close spacing. Otherwise the yield may be seriously reduced, especially under short-season conditions.
By planting in hills and thinning gradually, plants usually can be kept in the single-stalk form at any distance apart, 1 foot, 2 feet, or 3 feet, but closer spacings are preferable. Not how many feet, but how many inches apart the plants should be is the practical question to be determined by local experiments. Fortunately such experiments are not difficult, and can be tried in ordinary fields of cotton, with changes only in thinning and spacing.
In single-stalk culture of Egyptian cotton under long-season conditions in Arizona a wide range of spacings can be used, any of them better than uncontrolled branching. Yields of over a bale per acre have been obtained from single-stalk plants 2 feet apart in the rows, and also from plants only 4 inches apart, as well as from several intermediate spacings, 6 inches, 8 inches, 12 inches, and 18 inches, but usually with distinct advantages for the closer spacings, when comparisons are made in adjoining plots. Even with rows only 2.5 feet apart and the plants spaced at 4 inches in the rows, the yield was large. Rows 3.5 feet apart with plants 6 to 8 inches apart in the rows has been the most successful arrangement used thus far on a large scale, but in the more luxuriant fields the rows meet across the lanes and many of the lower fruiting branches are smothered. For conditions of rank growth experiments are now to be made with rows 4 feet apart and plants 4 inches apart, as an arrangement likely to give somewhat more effective control of growth and branching in the early stages, and less crowding between the rows.
Wide spacing and early thinning continue to be tried by farmers who have not had experience with Egyptian cotton under the Arizona conditions, but crowding is only made worse when the branching is not controlled. Fields of overgrown plants become veritable jungles of dense foliage and heavy wood limbs, with low yields of fiber, not of the best quality and difficult to pick. Thinning first to 4 inches will allow more space to be given later in the season, after the stage of producing vegetative branches is past, by pulling out every second or third plant, if experiments prove that sufficient advantage can be gained to justify the additional labor. With ordinary stands thinning to 4 inches may be done when the plants are from 6 to 10 inches tall, and further thinning at any later stage, when it appears that the plants are becoming crowded to an extent that is likely to reduce the yield or impair the quality of the fiber.
With upland cotton in Texas there may not appear to be the same need of controlling the growth of the plants by cultural means, since growth is often restricted by cold or dry weather, but it is essential that bolls be set and retained early in the season since drouths or boll weevils usually interfere with the production of a late crop. The period of setting bolls may be very short, as in the experiments described by Rowland M. Meade in 1914 at San Antonio, Texas, when nearly all of the bolls were set within about 25 days. In this case more than twice as much cotton was produced from small single-stalk plants standing only 6 to 8 inches apart in the rows than from large spreading plants thinned early to 2 feet apart that developed large vegetative branches. Tho results would not differ so widely in longer fruiting seasons, there is no reason to expect in any year that more cotton per acre can be produced on large spreading plants. Differences of 20 to 50 percent in yield are not infrequent, and afford sufficiently striking examples of the utility of branch control.
Earliness, in the practical sense of increased production in shorter fruiting periods, cannot be determined from first dates of flowering or of opening of bolls, but is shown by the setting of more bolls and the maturing of a larger crop. Nevertheless, any differences of behavior that can be observed and recorded are likely to be of interest or of practical use in tracing effects back to their causes and thus learning how the principle of control may be applied to the best advantage. Features that can be used for such comparisons are the size or rate of growth of the main stalks, the numbers, lengths, and positions of the two kinds of branches, the dates and rates of flowering and opening of bolls, numbers of bolls with 3, 4 or 5 locks, and weights of seed cotton from the different classes of bolls, in addition to the lint and seed characters which usually receive attention.
Control of branching may be considered successful when comparisons show practical advantages in larger yields or earlier ripening of the crop, but this does not prove that the full possibilities of the system have been realized in any particular test. That partial control or over-control may be better than no control, only shows that it is desirable to go further and determine the most effective utilization of the principle, thru local experiments and comparisons of behavior. It is only in this way that adequate discrimination and skill can be developed in the handling of different varieties and types of cotton under the wide range of cultural and seasonal conditions that are encountered in practice.