Irrigation, Water Management and Soil Conservation
What this domain covers
This domain tests irrigation sources and methods, scheduling at critical stages, water measurement, drainage, and soil and water conservation measures suited to Assam.
Core rules and concepts
- Sources: river, canal, tank, open well, tube well and rainwater harvesting.
- Methods: surface irrigation (flood, furrow, basin, border), subsurface irrigation, sprinkler (light soils, undulating land) and drip (water-scarce areas, orchards and wide-row crops).
- Scheduling: irrigate at critical stages and use the irrigation water to cumulative pan evaporation ratio. Rice is most sensitive at panicle initiation and flowering; mustard at flowering and siliqua filling.
- Water measurement uses weirs, flumes and water meters. Drainage is essential in high-rainfall and flood-prone areas.
- Assam receives about 2,000-3,000 mm of rain but faces winter moisture stress, so supplemental rabi irrigation is essential. Floods and bank erosion are the main land threats.
- Soil conservation: contour bunding, terracing, check dams, vegetative barriers, strip cropping, mulching, cover crops, agroforestry and control of shifting cultivation.
Worked example
Irrigation water of 5 cm depth is applied and the recommended IW/CPE ratio is 0.8. Irrigate when cumulative pan evaporation since the last irrigation reaches 5 / 0.8 = 6.25 cm. The reasoning is that the ratio links water applied to atmospheric demand, so scheduling responds to weather rather than a fixed number of days.
Traps that cost marks
- Confusing sprinkler (sprays water like rain) with drip (delivers water at the root zone).
- Assuming heavy rainfall removes the need for rabi irrigation in Assam.
- Irrigating at midday, when evaporation loss is highest.
- Ignoring drainage, which causes waterlogging and root disease.