Agronomy: Tillage, Planting Geometry, Water and Weed Management
Agronomy questions test the how behind crop statistics: tillage, sowing geometry, irrigation scheduling and weed control.
Tillage
- Primary tillage breaks the hard pan with a mould-board or disc plough; secondary tillage uses harrows and levellers to crush clods and level the field.
- Conservation and minimum tillage reduce erosion on the light soils of western Rajasthan; zero tillage is used in wheat, particularly after a late-puddled rice crop.
- Deep ploughing once in two or three years is advised for saline-sodic and light-textured soils to leach salts and break the pan.
Sowing and geometry
- Methods: broadcasting, drilling, dibbling, transplanting and ridge-and-furrow sowing.
- Plant population per hectare = 10,000 divided by (row spacing in metres multiplied by plant spacing in metres).
- Seed rate rises with test weight and falls with germination percentage and purity; always adjust for a poor germination test.
Water management
- Critical stages: crown-root initiation for wheat, branching for mustard, pre-flowering for gram, flowering for groundnut.
- Scheduling by IW/CPE ratio, the irrigation water depth divided by cumulative pan evaporation, commonly 0.8 for wheat and 0.6 for mustard.
- Drip and sprinkler systems under PMKSY raise water-use efficiency in desert districts where irrigation is scarce.
Weed management
- The critical period of crop-weed competition is roughly 30-45 days after sowing for most field crops.
- Integrated control: stale seedbed, pre-emergence herbicide such as pendimethalin, one hand weeding, then a post-emergence option if the population crosses the economic threshold.
Worked example
Wheat sown at 60 cm by 20 cm gives 10,000 divided by (0.6 multiplied by 0.2) = 10,000 divided by 0.12 = 83,333 plants per hectare. If 15% of plants are lost to poor germination and crusting, the effective stand falls to about 70,800, so the seed rate must be raised by roughly 18%.
Traps
- Converting centimetres to metres wrongly: 20 cm is 0.2 m, not 2 m.
- Mixing IW/CPE ratio with irrigation interval.
- Giving plant population when the question asks for seed rate.