Crop Science — Agronomy, Plant Pathology & Entomology
Agronomy Fundamentals
Agronomy is the science of managing field crops for food, feed, fibre, and fuel production.
Soil-Water-Plant Relationship
Soil texture (particle size):
•Clay: < 0.002 mm — highest water holding capacity, sticky, poor drainage
•Silt: 0.002–0.05 mm — moderate properties
•Sand: 0.05–2 mm — low water holding, fast drainage, easy tillage
•Loam: Mix of sand, silt, clay — ideal for most crops
Soil pH and crop preference:
| pH Range | Crops |
|---|
|----------|-------|
| 4.5–5.5 (acidic) | Tea, blueberries, rice (flooded) |
|---|---|
| 5.5–6.5 | Potato, maize, groundnut |
| 6.0–7.0 (optimal for most) | Wheat, soybean, vegetables |
| 7.0–8.5 (alkaline) | Barley, sugarbeet, date palm |
Water holding capacity (WHC): Maximum water a soil can hold against gravity.
•Clay > Loam > Sand (reverse for drainage rate)
•Field capacity: Soil water after gravity drainage
•Permanent wilting point: Water content at which plants wilt permanently (15 bar suction)
•Available water: Field capacity − Permanent wilting point
Major Field Crops — Agronomy
Rice (Oryza sativa)
•Season: Kharif (upland, lowland, deepwater varieties)
•Optimum temperature: 20–35°C
•Water requirement: 1,200–2,000 mm per season
•Major varieties: IR 64, MTU 7029 (Swarna), Pusa Basmati 1, Sona Mahsuri, Jaya
•Key HYV revolution: Green Revolution — IR8 (Miracle Rice, 1966)
•Cultivation: Nursery → transplanting (25–30 days old seedlings) OR direct seeded
•Major diseases: Blast (Magnaporthe oryzae), Brown Spot, Bacterial Leaf Blight (Xanthomonas)
•Major pests: Brown Plant Hopper (BPH), Yellow Stem Borer, Leaf Folder
Wheat (Triticum aestivum)
•Season: Rabi (October–November sowing, March–April harvest)
•Optimum temperature: Cool — 10–15°C growing, 25°C at ripening
•Water requirement: 400–500 mm (5–6 irrigations)
•Varieties: HD 2967, HD 3086, GW 496, PBW 343, Lok 1
•Green Revolution: Norin 10 dwarf genes → Norman Borlaug → Mexican wheats → India's adoption 1966
•Diseases: Rust (stem, leaf, yellow/stripe) — Puccinia spp., Loose smut, Karnal Bunt
•Critical growth stages: Crown Root Initiation (CRI, 21 days), Jointing, Flowering
Cotton (Gossypium)
•Species: G. hirsutum (American upland, 95% of India's cotton), G. arboreum (desi), G. barbadense (extra-long staple)
•Season: Kharif (April–May sowing)
•Temperature: 21–35°C; requires 180–200 frost-free days
•Bt cotton: Transgenic cotton expressing Cry1Ac and Cry2Ab proteins from Bacillus thuringiensis — toxic to bollworms
•Major pest: Bollworms (American, spotted, pink) — Bt cotton controls; sucking pests (whitefly, jassid, thrips) — managed by insecticides
Sugarcane (Saccharum officinarum)
•Perennial crop; ratoon cropping common (3–5 ratoons)
•Temperature: 21–38°C; needs hot dry weather at maturity for sugar accumulation
•Water: Most water-intensive — 1,500–2,500 mm
•Key disease: Red rot (Colletotrichum falcatum) — most destructive in North India
•By-products: Bagasse (fuel, paper), molasses (ethanol, yeast), press mud (compost)
Plant Pathology — Major Diseases
Disease Triangle: Host × Pathogen × Environment
All three must be favourable for disease to occur.
Types of pathogens:
1.Fungi: Larges