Irrigation and Water Management
What this domain covers
Irrigation and Water Management tests water sources, irrigation scheduling, methods and efficiency. Haryana depends on canal water and tubewells, and the exam often links over-irrigation to waterlogging, salinity and falling water tables.
Core rules and concepts
- Know soil moisture constants: field capacity, permanent wilting point and available water. Irrigation should be applied before stress, not after wilting.
- Critical stages differ by crop: wheat at crown root initiation, tillering, jointing, flowering and milk; rice at transplanting, panicle initiation and flowering; mustard at flowering and pod formation.
- Scheduling can use soil moisture, pan evaporation or the IW/CPE approach. Light, frequent irrigation suits sandy soils; heavier, less frequent irrigation suits clay loams.
- Methods: flood, furrow, border, sprinkler and drip. Drip and sprinkler raise water-use efficiency; laser levelling improves flood irrigation uniformity.
- Avoid over-irrigation. It leaches nutrients, raises the water table and can cause secondary salinity. Provide drainage where waterlogging is a risk.
- Mulching and residue retention reduce evaporation. Micro-irrigation is promoted under PMKSY.
Worked example
A soil has field capacity 28%, permanent wilting point 12% and bulk density 1.4 g/cm³ over a 60 cm root zone. Available water = (28 − 12)% × 60 cm × 1.4 = 13.44 cm, or about 134 mm. If irrigation is given at 50% depletion, the net depth is about 67 mm. Reasoning: the calculation converts gravimetric water content to a depth of water; it prevents the common mistake of irrigating by calendar alone.
Traps that cost marks
Do not irrigate every field on the same day regardless of soil and crop stage. Do not ignore drainage when applying heavy irrigation. Do not confuse gross irrigation with net irrigation; field application losses must be added.