Principles of Agronomy and Crop Production
Agronomy applies soil, climate, and crop management to field production. The Tamil Nadu Higher Secondary Agricultural Science paper tests cropping systems, crop geometry, package of practices, and the reasoning behind seed rate and plant population.
Cropping systems and rotation
- Sole cropping: one crop in a field in a season.
- Mixed cropping: two or more crops sown together without a fixed row arrangement; harvested together.
- Intercropping: crops in definite rows, e.g., cotton + blackgram; the main crop and intercrop are harvested separately.
- Sequence cropping: one crop after another in the same year; relay cropping overlaps the next crop before the first is harvested.
- Rotate with legumes such as blackgram or cowpea to add nitrogen and break pest cycles; avoid repeating the same plant family.
Crop geometry and establishment
Seed rate depends on spacing, germination, and seedling survival. Plant population per hectare = 10,000 ÷ (row spacing in m × plant spacing in m). Tillage prepares a seedbed; primary tillage is deep ploughing, secondary tillage refines the surface. Weed control combines preparatory tillage, crop competition, and mechanical or herbicidal control.
Worked example
Cotton at 75 cm × 30 cm: area per plant = 0.75 × 0.30 = 0.225 m². Plants per hectare = 10,000 ÷ 0.225 = 44,444. If germination is 80% and 10% seedlings are lost, sow approximately 44,444 ÷ (0.8 × 0.9) = 61,728 seeds per hectare. This shows why field seed rate exceeds the theoretical plant stand.
Traps that cost marks
Do not confuse mixed cropping with intercropping: intercropping uses rows and separate harvests. Do not put seed rate in kg when the question asks for plant population. Convert centimetres to metres before dividing. Remember that a legume in rotation improves nitrogen, but it does not replace a full fertilizer recommendation.