Climatic requirements of cotton

Warm season (tropical) crop. Cotton can be profitably grown in regions with rainfall of 850-1100 mm. However, economic yields can not be realized in the region with a rainfall less than 500 mm. 50cm of well-distributed rainfall is necessary for higher yields.

• Production depends on vagaries of monsoon since 2/3 cotton area is rainfed.
• Very sensitive to water logging (both shading).
• Rains during boll bursting period spoil the cotton quality.
• Cotton requires at least 450-500 mm of water for ET inorder to give higher yields.
• Very sensitive to low temperature during the period of floral bud initiation during which temperatures of 21 degree C and above are desirable.
• During flowering and fruiting, temperatures of 26-32 degree C are desirable during the daytime, but the nights should be cool.
• In general, temperatures above 35 degree C are not desirable, however, when the moisture supply is favourable, the cotton plant is capable of enduring without permanent injury, very high temperatures (upto 43-45 degree C) for short periods. If these high temperatures persist for several days, however, the yields will be adversely affected.
• During maturation of bolls and fibres, which is essentially a drying process, relatively high temperatures are desirable with an average daily temperature of 22 degree C, 68 days were required for boll maturation when the average daily temperature approaches 38 degree C, the period of maturation is still further shortened, but the bolls are smaller and the fibres do not develop fully, and yields are reduced. For optimal development and high quality of the fibres, hot and clear days are required. Under these conditions the quantity of fibres per boll increases, and the fibre is somewhat shorter but thicker and stronger than otherwise provided that the moisture supply is adequate.
• When soil temperature fall below 20 degree C, even for short periods, the uptake of water is slowed down, and the cotton plants may wilt even when there is ample soil moisture.
• At still lower soil temperatures (below 10 degree C) the geotropism of the cotton roots is affected, and abnormal root-growth results.
• Excessively high soil temperatures (>40 degree C) also have adverse effects.
• High light intensities throughout the growing period are essential for satisfactory vegetative development, for minimal shedding of buds and bolls and hence for higher yields.
• Reduced light intensities, as a results of cloudiness, reduce the rate of boll-set and cause excessive vegetative development. The increased shedding that is frequently observed following rains which occur during the cotton's growing period, can probably be ascribed to the reduced light intensity rather than to the effects of the rainfall per
• Reducing light intensity to one-third of normal, reduced carbohydrate content of the leaves by 24 percent, of the stems by 38 percent, and of the bolls by 8 percent, the cotton yield being reduced by 47 percent.
• All wild species of Gossypium are short-day plants and do not flower so long as the day-length exceeds twelve hours.
• Present-day cultivated varieties are generally insensitive to day length.
• Cannot tolerate frost (180 - 240 frost free days in North is required)
• Crop can be grown up to 1000m altitude

Climate Criteria for Cotton



Item	Degree of Limitation and Suitability Class
	None	Slight	Moderate	Severe
	S1	S2	S3	N1
I. Climatic Parameters
Total rainfall (mm)	850-1050		550-700	< 550
Rainfall during growing season	750		450	< 450
Rainfall during boll development (90-120 days after sowing)	100-200		60-80	< 60
Length of growing period (days)	160-180		120-140	< 120
Mean temp in celciusin growing season	22-28		> 32
Mean maximum temperature				< 36
Mean minimum temperature				> 19
Mean relative humidity in growing season	60-80			< 50
Length of dry spell (in days) At seedling stage - At boll development	< 7 < 14	7-10 14-21	10-15 21-28	> 15

S1= most suitable, S2=suitable, S3=marginally suitable, N1=non suitable could be improved N2=permanently unsuitable.

Soils

Cotton has a wide range of soil adaptation and is grown on a great variety of soils. Highest yields of cotton are usually obtained on alluvial soils. High yield of cotton is dependent on favorable air and moisture regime in the soil-hence the importance of soil structure and texture.

• For a deep-rooting crop such as cotton, soil depth is also an important factor and shallow soils are not suitable.
• Cotton is not unduly sensitive to soil reactions; it can be grown on a variety of soils with pH ranging from 5 to 8 and above.
• Cotton is generally considered as fairly tolerant to salinity. Uptake of Sodium by cotton has been found to be much lower than would be expected from its relative abundance and availability in soil and water as was shown by the low accumulation of sodium in both tops and roots. This indicates that the relatively high salt-tolerance of cotton may be at least partly due to the presence of some selective mechanism that enables cotton roots to restrict sodium absorption.
• Under moderate rainfall conditions cotton is grown as retentive clayey loams.
• With irrigation facilities, cotton is usually cultivated on sandy loam to loam soils.
• Humus content may be < 1 to > 5%. Adequate Organic matter in light soils improves water holding capacity and improves drainage and aeration in heavy soils.
• Highly calcareous soils with more than 30% free Ca Co3 may cause phosphorus fixation and micronutrient deficiency.

• North Zone : Loamy & sand loamy soils are suitable
• Central & South Zone : Deep vertisols are suitable for growing long duration hybrids vertic inceptisols are most suitable with higher economic returns for cultivation of early maturity hybrids and improved varieties.
• Soils to be avoided : Slopy, shallow overlying an impermeable rock, poorly/excessively drained and calcareous soils where Water retention is poor and root development is restricted.

Soil-Site criteria for cotton