Irrigation, Water Management and Dryland Agriculture
Irrigation, Water Management and Dryland Agriculture - This domain tests water requirement, irrigation scheduling, methods and moisture conservation in rainfed areas.
Core rules
- Water requirement = crop evapotranspiration plus losses; effective rainfall reduces the irrigation need.
- IW/CPE ratio: irrigate with a fixed depth (IW) when cumulative pan evaporation (CPE) reaches a set value; common ratios are 0.8–1.0.
- Critical stages: rice panicle initiation, wheat crown root initiation, maize tasseling, groundnut flowering–pegging, mustard flowering.
- Methods: flood, furrow, sprinkler and drip; drip saves the most water and suits horticultural crops.
- Dryland measures: contour bunding, compartmental bunding, mulching, rainwater harvesting, drought-tolerant varieties and intercropping.
Worked example
A 50 mm irrigation is applied when CPE reaches 40 mm. IW/CPE = 50 ÷ 40 = 1.25. If CPE is 40 mm and effective rainfall is 10 mm, the net irrigation need is 50 − 10 = 40 mm. Reasoning: CPE estimates evaporative demand; the ratio is a scheduling index, not a measure of irrigation efficiency.
Traps
- CPE is not crop evapotranspiration; it is evaporation from an open pan.
- Flood irrigation is not the most efficient method.
- Critical stages differ by crop; crown root initiation is wheat, not rice.
- In dryland agriculture, mulching conserves moisture but does not replace rainfall.
- Drip irrigation reduces evaporation and deep percolation but still needs scheduling.