Cotton is a highly adaptable plant and it can be cultivated in a wide variety of soils. High yields are achieved in deep, fertile soils of medium mechanical composition, with adequate drainage and good moisture capacity.
In sandy soils, it requires increased fertilization. Heavy soils retain water, which suffocates and causes diseases to the root system, and it is therefore unsuitable for cultivation.
Cotton is quite tolerant to soil salinity. Regarding acidity, it grows in a wide pH range, from 5,5 to 8,0, ideally within 6,8-7,3.
It is a warm climate plant, requiring high temperatures during growth and fruiting. During sowing, the ideal soil temperature for adequate sprouting in the field is 13οC, while the ideal atmospheric temperature for fast growth and high yields is 32οC-34oC.
From emergence to squares
The proper temperature and adequate moisture in the soil are necessary conditions for a uniform growth of the seeds.
From emergence until the 5th node, it is mainly the roots which are growing while vegetative growth remains limited. After the 5th node, as temperatures rise, vegetative growth is accelerated, with the emergence of vegetative and then fruiting branches on which the squares, flowers, and bolls will form.
At this stage, it is essential that the following have been achieved: strong establishment of the crops in the soil, development – both in depth and in volume – of the root system, and the formation of plants with a rich leaf area, all of which should contribute to increased flowering, strong fruit setting, and boll growth at later stages.
Basic fertilization is crucial to crop yields, as it secures the necessary quantities of Nitrogen (Ν), Phosphorus (Ρ) and Potassium (Κ) for early plant growth.
Without basic fertilization, crops exhibit deficiencies and enter the reproductive stage without having achieved the necessary vegetative growth. This leads to a loss of produce which cannot be counterbalanced by later fertilization or other cultivation practices.
Nitrogen (Ν) stimulates vegetative growth, enhances photosynthesis, and increases the height of the plants and the number of branches, leaves, and squares.
Phosphorus (P) boosts the growth of the root system and strong establishment of the plant in the soil, and it contributes to the development of the meristems on which the branches, leaves, and squares will grow.
Potassium (Κ) boosts root and leaf growth, enhances photosynthesis, improves water absorption, and protects the crop from diseases and adverse weather conditions. It also improves plant endurance against adromycosis.
Magnesium (Mg) increases the number of leaves and the photosynthetic activity of the plants.
From the emergence of squares to the onset of flowering
The phase of reproduction begins with the emergence of the first flower buds (squares) mid-June, and it is one of the most crucial stages, as the crop both enters the reproductive stage and continues with the vegetative growth at the same time. The plants produce new branches and grow their roots at a maximum rate, and the crop covers the entire field, both over and under the surface of the soil.
The goal is to have the best possible vegetative growth in balance with fruiting so they do not compete with each other, resulting in excessive shading of the lower leaves, delayed flowering, square/flower shedding, and boll shedding later on.
During this period the plants are extremely sensitive to lack of water, extreme temperatures, lack of light, and insufficient nutrients, particularly Nitrogen, Potassium, Boron and Zinc.
The requirements in Potassium during this time need to be covered by basic fertilization, while the requirements in Nitrogen by top-dressing fertilization before flowering.
Trace elements, Boron and Zinc, which are essential to the crops, need to be supplied either by basic fertilization, or by top-dressing fertilization with Nitrogen fertilizers containing them, or by applications between the leaves during the formation of the squares.
Nitrogen (Ν) increases the production of flowering branches and flowers and boosts the growth of flower parts.
Phosphorus (P) contributes to the crop entering the phase of reproduction in time and to the formation of the flower organs.
Potassium (Κ) increases the production of squares and flowers and the photosynthetic activity of the leaves. It reduces the cut-off of reproductive organs, balances the adverse effects of any Nitrogen surplus, and it regulates the water balance of the plant.
Boron (Β) and Zinc (Zn) increase the production and fertility of pollen, improve flowering and fruit setting, participate in the early development of the bolls, and they reduce shedding of the latter.
From fruit setting to boll maturation
Productive flowering begins three weeks after the emergence of squares (early July) and lasts for six weeks (mid-August). At the early stages of flowering, fruit setting is high; it is gradually reduced after the 4th week.
The bolls develop fast and come into their final size three weeks after fruit setting, while it takes about four more weeks for them to mature and open.
The fibers appear right after fruit setting. First (15-25 days) they grow in length, while they increase in width during boll maturation.
During this time, the requirements of the plants in nutrients, water, and carbohydrates are maximized in order to cover the needs of boll increase, seed formation, and fiber growth.
Any deficiencies in Nitrogen and Potassium, combined with unfavorable weather conditions and diseases, lead to square and boll shedding, seeds and bolls of lower weight, and lower quality fibers.
Nitrogen (Ν) increases the number and weight of the bolls which remain on the plant, the weight of the seeds, and the ratio and length of the fibers.
Phosphorus (P) leads to earlier maturation and increases the weight of the bolls and seeds, as well as the diameter and resilience of the fibers.
Potassium (K) increases the length and width of the fibers, as well as the weight and oil content of the seeds.
Basic fertilization (during sowing)
The target is to cover the needs of the plant in nutrients which are necessary for its strong establishment, the formation of a rich root system, and an early and robust vegetative growth.
Without basic fertilization, nutrient uptake is insufficient at the early stages, due to low temperatures and limited root growth. The plants exhibit deficiencies and the result is loss of produce which cannot be counterbalanced by later fertilization or other cultivation practices.
Linear application during sowing facilitates the uptake of nutrients, particularly of Phosphorus and Potassium, which are slowly available in the soil.
- 1/2 of Nitrogen (Ν)
- The full amount of Phosphorus (P)
- The full amount of Potassium (Κ)
The Nitrogen supplied through basic fertilization needs to be in Ammoniacal form so that it remains readily available to the plants throughout the entire period from sprouting to flowering.
The use of multinutrient (Nutrifert) or compound stabilized (NutrActive) fertilizers is recommended. Enriched with the trace elements of Boron and Zinc, these fertilizers successfully provide the crops with integral nutrition, minimize losses, and ensure a robust growth of the root system and vegetation.
Top-dressing fertilization (before the emergence of the squares)
The target is to cover the needs of the plant in nutrients which are necessary for vegetative growth in the summer, flowering and fruit setting, as well as the development of the bolls. Early application, before the emergence of the squares, is conducive to the timely entrance of the plants in the phase of reproduction.
Ammoniacal Nitrogen increases flowering and reduces square, flower, and fruit shedding, which are caused when vegetative growth and fruiting compete with each other.
It is recommended that either Nitrogen fertilizers with high content in Ammoniacal Nitrogen (Fertammon) or stabilized Ammoniacal Nitrogen (NutrActive), which reduce Nitrogen losses from the soil and secure and adequate supply of the crops until the final stages of boll filling, be used once, or that Nitrogen be supplied in installments through the fertigation systems in the form of Ammonium Nitrate (Nutrammon solub), which provides the crops with a balanced ratio of Ammoniacal and Nitrate Nitrogen.