Do different cotton varieties require different fertilization methods, and what are the similarities and differences?

Recently, when the author visited cotton-producing areas in counties and cities such as Tianmen, Hanchuan, Jingshan, and Jianli, as well as Huarong, Anxiang, and Nanxian in Hunan Province, many farmers asked about cotton fertilization techniques. They often regard fertilization as one of the important means of increasing yield, so they show great concern about fertilization techniques.

Years of experience and lessons in cotton fertilization tell us that the common experience for increasing cotton yield through fertilization is: apply sufficient basal fertilizer, apply seedling fertilizer quickly, apply bud fertilizer steadily, apply flower and boll fertilizer heavily, and apply boll fertilizer universally. However, when it comes to different cotton varieties, there are differences in fertilizer application.

Cotton varieties are divided into conventional varieties and hybrid varieties, and within these two categories, there are also early-maturing varieties, medium-maturing varieties, and late-maturing varieties.

Generally speaking, conventional cotton varieties and conventional hybrid cotton varieties require less potassium fertilizer, while genetically modified insect-resistant cotton, especially genetically modified hybrid insect-resistant cotton, is quite sensitive to potassium fertilizer. According to field production practice in recent years, their demand for potassium fertilizer is often more than double that of non-insect-resistant cotton, requiring 60 jin or even more per mu of potassium fertilizer with an effective content of 60%.

Early-maturing varieties have a relatively shorter growth period. These varieties generally set bolls quickly and concentratedly in the early stage, and their demand for fertilizer in the early stage is relatively large. If fertilizer is insufficient in the early stage, premature aging often occurs in the later stage, the lower leaves lose fertilizer quickly, and in severe cases they appear scorched; the upper fruiting branches cannot extend, and the growing point tip lacks staying power. For these early-maturing varieties, if flower and boll fertilizer or boll fertilizer cannot be applied in time, it can easily lead to reduced cotton yield and income. For these cotton varieties, sufficient basal fertilizer must be applied in the early stage, sufficient flower and boll fertilizer must be applied in the middle and late stages, and in particular, boll fertilizer must be widely and properly applied. When a single cotton plant has already set more than 3 mature bolls, the urea topdressing per mu should be no less than 30 jin. Cotton fields where potassium fertilizer was insufficiently applied in the early stage also need supplementary potassium fertilizer.

Late-maturing cotton varieties generally have relatively vigorous vegetative growth in the early stage. For these varieties, first, the total amount of fertilizer applied per mu should be controlled; second, excessive application of nitrogen fertilizer should be controlled. If there is too much nitrogen fertilizer or the total amount of fertilizer applied is too large, when cotton enters the full squaring stage or the flower and boll stage, vegetative growth will often inhibit reproductive growth, making the growth period of late-maturing cotton varieties even later. It will also cause cotton to close rows too early, with severe shading, aggravating bud and boll shedding and boll rot. When fertilizing these cotton varieties, early-stage fertilization must be kept steady. First, the amount of nitrogen fertilizer must be strictly controlled. Second, the total amount of fertilizer applied per mu must be controlled. For example, when applying basal fertilizer, a compound fertilizer with a nitrogen, phosphorus, and potassium content of 45% per mu should not exceed 80 jin. Third, it is advocated to mainly apply compound fertilizer or various biological organic compound fertilizers, and it is best to apply these two types of fertilizer together. Fourth, chemical regulation should be done well to shape a high-yield plant type. Fifth, it should be combined with thorough pruning and removal of branches to enhance ventilation and light penetration between cotton rows. Of course, because these varieties have relatively strong staying power and more autumn bolls, topdressing boll fertilizer should not be neglected either. Apply 20~30 jin of urea per mu as boll fertilizer as appropriate, supplemented by foliar topdressing.

As for the fertilization of medium-maturing cotton varieties, it falls between early-maturing and late-maturing cotton varieties, and can be flexibly managed according to local climate, soil, and seedling conditions.