Agronomy of Fiber Crops: Cotton, Jute, Mesta, and Sunnhemp

Fiber crops are cultivated primarily for their textile, cordage, and industrial fibrous materials derived from seed hairs, bast tissues, or surface leaves. Understanding their botanical classification is vital for competitive agronomy examinations.

• Cotton (Kapas): Belongs to the family Malvaceae. Cultivated species include Gossypium hirsutum (American upland cotton, 2n=4x=52), Gossypium barbadense (Egyptian or Sea Island cotton, 2n=4x=52), Gossypium arboreum (Tree cotton, 2n=2x=26), and Gossypium herbaceum (Levant cotton, 2n=2x=26).
• Jute (Pat): Belongs to the family Tiliaceae (or Malvaceae under APG IV). Two primary cultivated species are Corchorus capsularis (White jute, round pods, 2n=2x=14) and Corchorus olitorius (Tossa jute, elongated pods, 2n=2x=14).
• Mesta: Also known as kenaf or roselle, belonging to Malvaceae. Major species are Hibiscus cannabinus (Kenaf) and Hibiscus sabdariffa (Roselle).
• Sunnhemp: Belongs to Fabaceae (Leguminosae) and is scientifically known as Crotalaria juncea (2n=2x=16), serving both as a fiber and a green manure crop.

Fiber crops exhibit distinct climatic and edaphic adaptations across the diverse agro-climatic zones of India, especially the Indo-Gangetic plains and central cotton-growing tracts.

• Cotton: Thrives in warm, sunny climates with a frost-free period of at least 200 days. Requires a temperature range of 21°C to 30°C during growth and abundant sunshine during boll maturation. Prefers deep, well-drained alluvial soils of the northern plains and heavy black vertisols of central India.
• Jute: Requires a warm and humid climate with heavy rainfall (1000 to 2000 mm) and high relative humidity (70% to 90%). Temperature ranges between 24°C and 38°C are optimal. Grows best on fertile alluvial soils of river basins that receive annual silt deposits.
• Soil pH and Drainage: Waterlogging is highly detrimental to cotton, causing boll shedding and root rot. Jute tolerates temporary waterlogging during the monsoon season. Optimal soil pH for cotton is 6.0 to 8.0, whereas jute prefers slightly acidic to neutral soils (pH 6.0 to 7.5).

Establishment of an optimal plant population is critical for maximizing the economic yield of fiber crops.

• Land Preparation: Fine tilth is required for cotton and jute. Deep ploughing followed by harrowing and planking ensures proper moisture conservation and weed eradication.
• Seed Rate and Spacing:
  • Desi Cotton (G. arboreum): Seed rate 12-15 kg/ha; Spacing 45-60 cm × 15-30 cm.
  • American Cotton (G. hirsutum): Seed rate 15-20 kg/ha; Spacing 67-75 cm × 30-45 cm.
  • Hybrid Cotton: Seed rate 1.5-2.0 kg/ha (dibbling); Spacing 90-100 cm × 45-60 cm.
  • Jute (C. capsularis & C. olitorius): Line sowing seed rate 6-8 kg/ha; Broadcasting seed rate 10-12 kg/ha; Spacing 30 cm × 5-7 cm.
• Seed Treatment: Cotton seeds are acid-delinted using concentrated sulfuric acid (100 ml per kg of seed for 2-3 minutes) to remove fuzz, followed by washing and treating with Trichoderma viride (10 g/kg) and Azotobacter. Jute seeds are treated with carbendazim at 2 g/kg of seed to prevent seed-borne fungal infections.

Nutrient uptake in fiber crops is heavy, requiring balanced application of nitrogen, phosphorus, and potassium (NPK) along with secondary and micronutrients.

• Cotton Fertilizer Dose: Recommended N:P:K for rainfed hybrid cotton is 80:40:40 kg/ha, while irrigated hybrids require up to 120-150:60:60 kg/ha. Nitrogen is applied in splits (basal, square formation, and flowering stages) to prevent excessive vegetative growth.
• Jute Fertilizer Dose: Typically requires 60 to 80 kg N, 30 kg P₂O₅, and 30 kg K₂O per hectare. Nitrogen is applied in two equal splits—half as basal and half after the first weeding and thinning (at 20-25 days after sowing).
• Micronutrient Deficiencies: Boron deficiency in cotton leads to flower bud shedding and twisted bolls; foliar spray of boron (Solubor at 0.2%) during square formation is recommended. Zinc deficiency causes interveinal chlorosis.

Fiber crops face severe biotic stresses that can drastically reduce commercial lint and fiber yields.

• Insect Pests of Cotton:
  • Pink Bollworm (Pectinophora gossypiella): Larvae feed on developing seeds and fibers inside the boll. Managed using pheromone traps (5/acre), release of Trichogramma, and transgenic Bt cotton hybrids.
  • American Bollworm (Helicoverpa armigera): Polyphagous pest damaging squares, flowers, and bolls.
  • Jassids (Amrasca devastans): Sucking pest causing hopper burn (curling and yellowing of leaves).
• Diseases of Cotton:
  • Bacterial Blight (Xanthomonas citri pv. malvacearum): Angular leaf spots and black arm symptoms. Managed by seed treatment with copper oxychloride and streptomycin.
  • Fusarium Wilt (Fusarium oxysporum f. sp. vasinfectum): Vascular wilt leading to yellowing and defoliation.
• Diseases of Jute:
  • Stem Rot and Root Rot (Macrophomina phaseolina): Causes bark rotting and seedling blight. Controlled by seed treatment with carbendazim and avoiding water stagnation.
  • Anthracnose (Colletotrichum corchori): Lesions on stems and leaves.

Post-harvest processing distinguishes fiber crops from cereal and pulse production, requiring specialized extraction and grading techniques.

• Cotton Harvesting: Done in multiple pickings as bolls open fully. Avoid picking damp cotton or harvesting after sunset to maintain lint quality (cleanliness and color grade). Average yield ranges from 15-25 quintals/ha of seed cotton (kapas).
• Jute Harvesting: Harvested at the small pod/flower stage (around 120-135 days after sowing) for superior fiber strength and quality. Plants are cut close to the ground or pulled out.
• Retting Process in Jute: Retting is a biological process where bundles of harvested jute stems are submerged in slow-moving or stagnant retting water (34°C optimal). Microorganisms (pectinolytic bacteria like Clostridium and Bacillus species) dissolve plant gums and pectins, loosening the fiber from the woody core (xylem).
• Stripping and Storage: Fibers are extracted manually or mechanically by stripping, washed in clean water, dried in the sun for 2-3 days, and baled. Safe moisture content for jute storage is 12% to 14%.