Cotton

Introduction

• Soil in cotton growing areas have a low organic matter content ranged from 0.5 to 1.25 per cent, albeit cotton sheds residues like burs, leaves, flowers, etc., It responds to organic matter addition and green manuring in tropical India.
• Cultivar MCU-5 yielding 3.2 t/ha seed cotton removes 190 kg N, 61 kg P2O5 and 195 kg K2O per ha, the uptake of N, P, K, Ca & Mg was highest when leaf water potentials are maintained at - 0.8 to 1.0 Pa.

Manure and Fertilizers

• Based on the relative occurrence of nutrient deficiencies world wide, Heaon (1981) classified the nutrients into the following groups

• Under Indian conditions, deficiencies of N, P and K among major, Mg and S among secondary and Zn and B among micronutrients have been recorded under field conditions in cotton.

Chemical fertilizers:

Table : N, P and K fertilizers recommended for different zones

Organic manures: FYM / Compost : Irrigated – 10 t/ha

Rainfed - 5 t/ha

Organic manures should be incorporated in the soil 2-3 weeks prior to sowing. In case of irrigated condition, instead of FYM, poultry manure at the rate of 2 t/ha can be used.

Note: In irrigated and transitional tract, growing of sunhemp between two cotton rows and incorporation of sunhemp in the soil after 30 days, reduces the weed infestation increases the soil fertility and yield.

• Use of biofertilizers can reduce the fertilizer requirement as well as cost of cultivation. Inoculation of cotton seed with Azotobactor chrococcum (strains C2 or M4) or Azospirillum brazilense @ 200 g/kg seed results in saving of fertilizer N to the extent of 20 kg N/ha.

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Secondary and Micronutrients

• S deficiency is increasing in the intensive cotton growing regions in soils having low S status, response of up to 20 kg S ha-1 has been observed.
• In India, since cotton is growing on soils with 6.0 to 8.5 pH, the availability of Ca and Mg is not limiting. However, sometimes excess exchangeable Ca may lead to Mg deficiency. When the Mg content in the leaves at flowering stage, falls below 0.3 per cent, reddening of leaves is observed Mg deficiency can be corrected by soil or foliar application of MgSo4.

Zinc

• About 30-35 ppm Zn in mature cotton leaves is considered adequate in sandy loams. Zinc deficiency can be corrected by soil application of 20-25 kg ZnSO4 ha-1 or foliar application of 0.5 per cent ZnSO4.
• Boron deficiency has been associated with boll rot in cotton and can be corrected by foliar application of 0.1 per cent boric acid/soil application of 10 kg borax/ha.

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Nutrient deficiency symptoms

Nitrogen

• Plants expressing N deficiency show stunted growth with small, pale, chlorotic leaves and poor root system

Phosphorus

• P deficient cotton plants appear stunted with dark leaves. Accumulation of anthocyanin pigments may give a purplish colours to leaves.

• Petiole P values below 1000 mg/g indicates P deficiency.

Potassium

• Specific deficiency symptoms in cotton plants begin with a yellowish white mottling of leaves, accompanied by yellow spots between the veins. Veins appear darker. As the deficiency becomes more severe, yellow spots become whiter. Later the tips margins as well as the spots become brown and the leaves curl downwards while lamina becomes bronze and is shed. Fibres become shorter and less firm K deficiency aggravates wilt (Fusarium sp.) and Alternaria leaf spot diseases.

Sulphur

• Cotton deficient in S produce yellow leaves at the apex while older leaves remain green in contrast to N. Also, unlike N, S deficiency, the veins remain green.

Magnesium

• Mg deficient cotton plants develop purple red leaves with striking green or white veins. Older leaves are affected first and they senesce prematurely.

Zinc

• Zinc deficient cotton plants have cup shaped small leaves with interveinal chlorosis. Chlortic tissues become brown and broned as tissues die.

Boron

• B deficiency results in the shedding of squares, flowers and young bolls. The petioles of young leaves are irregularly thick red and on splitting open longitudinally, exhibit dark bonds with necrotic pith the terminal bud often dries.

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Integrated Nutrient Management

• It is recommended to supply the required nutrients in an integrated supply mode – wherein the nutrients are supplied both by organic and inorganic sources.
• It is established by many field experiments that ½ N by organic sources and remaining ½ N + full P and K as fertilizers will make ideal combination for integrated nutrient supply modes.
• Recently the Zinc and sulfur are supplied as enriched compost wherein manure is prepared along with in organic sources zinc and sulfur.
• Crop residue of green manure grown and recycled prior to cotton cultivation may be an ideal source of organic source of nutrients under irrigated conditions.

Red Leaf disorder

• In many parts of South India, red leaf disorder is reported with various intensities especially in hybrid cotton. It can reduce the yields from 10-50%.
• Red leaf disorder is a nutritional disorder aggravated by various climatic adversities. It can appear due to one or more following reasons:
• Poor soils with low N supply or fertilizer dose with inadequate N supply.
• Water stress for poor drainage in soil hampering the N availability and N absorption.
• Sudden reduction in night temperature arresting the translocation.
• The red leaf disorder is characteristically exhibited by reduced chlorophyll content upsetting. The balance between chlorophyll, anthocyanin proportion.
• The symptoms of red leaf are invariably on older leaves in the beginning and are found in younger leaves in severe situations.
• Besides red pigmentation, the leaves lose turgidity droop and wither away.
• In many field situation, fully reddened, partially redenned leaves are found – reducing the photosynthesis and yield.

It is recommended to spray 2% urea or 2% DAP at an interval of 3-5 days in the stress conditions.

Use of growth regulators / Micronutrients

Application of NAA (planofix) @ 4.5 ml/18 litre of water at the time of flowering stage will prevent the dropping of flowers and buds. Total of 800-1000 litre of spray solution is required for ha area. Similarly application of 2% Urea and 0.5% MgSO4 on the crop between 90 to 110 days after sowing will prevent cotton leaf reddening.

Water Management

• Water requirement of cotton crop varies from 50-70 cm depending upon duration and type of varieties.
• However , it cannot withstand standing water for a period more than 2-3 days.
• Due to excessive irrigation or prolonged water stagnation following consequences may be seen.

Irrigation

• Irrigation depends upon the soil type and environmental condition. Irrigate the crop twice before flowering and 4 times after flowering once in 10-15 days and 20-30 days in sandy loam and red loamy soils, respectively.
• In deep black soil, where the irrigation is not sufficient alternatively, alternate furrow irrigation is recommended.
• Drainage should be provided in deep black soil where the water logging is a problem.
• Irrigate the crop keeping optimum growth in view.
• Drip irrigation is recommended in seed production plot and in hybrid cotton. It is not only cost effective but also save the electricity and water. Drip irrigation varies with locality, environmental condition, crop growth and evaporation rate.
• Late irrigation in case of command area and early irrigation before sowing in open well situation is recommended.

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