Utility of Irrigation Systems and Water Management in Various Major Crops

Crop water requirement (ET_crop) encompasses the total water needed for crop growth, metabolic processes, and evapotranspiration under field conditions. Understanding water dynamics is critical for optimizing irrigation efficiency and maximizing water use efficiency (WUE) in Indian agriculture.

• Evapotranspiration (ET): The combined process of evaporation from soil surface and transpiration from plant tissues, measured in millimeters per day (mm/day).
• Consumptive Use (CU): The quantity of water used by vegetative growth of a crop area in transpiration and building of plant tissues, plus evaporation from soil and intercepted water.
• Water Use Efficiency (WUE): Defined as the ratio of crop yield (Y) to the amount of water depleted by the crop in evapotranspiration (ET), expressed in kg/ha-mm.
• Effective Rainfall: That portion of total precipitation that is effectively utilized by the crop for its growth needs, excluding runoff and deep percolation losses.

Cereals form the foundation of Indian food security, with wheat, rice, and maize requiring precise irrigation schedules aligned with phenological development phases.

• Wheat (Triticum aestivum): Requires 450–650 mm of water across 4 to 6 irrigations. The most critical stage is Crown Root Initiation (CRI), occurring 20–25 days after sowing (DAS). Other critical stages include tillering, jointing, flowering, milk stage, and dough stage.
• Rice (Oryza sativa): Demands 900–1500 mm of water. Continuous submergence of 5 cm is practiced, except during tillering drainage and 10 days before harvesting. Critical stages are panicle initiation, booting, flowering, and milking.
• Maize (Zea mays): Consumes 500–800 mm of water. Highly sensitive to moisture stress during tasseling and silking stages; water stress here causes severe yield reduction due to barren cobs.
• Pearl Millet (Pennisetum glaucum): Drought-tolerant crop requiring 250–350 mm. Critical stages are tillering and flowering.

Pulses and oilseeds are predominantly grown under rainfed (barani) conditions or with limited irrigation. Excess moisture during early growth is as detrimental as drought during reproductive phases.

• Chickpea (Cicer arietinum): Requires 200–300 mm of water. Two critical irrigations—one at pre-flowering (branching) and another at pod development—significantly boost yields. Excess water causes excessive vegetative growth and flower drop.
• Pigeonpea (Cajanus cajan): Highly sensitive to waterlogging. Requires well-drained soils; critical stages are pre-flowering and pod filling.
• Rapeseed and Mustard (Brassica juncea): Requires 200–250 mm. Critical irrigation stages are rosette growth (branching) and siliqua development.
• Groundnut (Arachis hypogaea): Demands 500–700 mm. Pegging and pod formation stages are extremely sensitive to water stress; moisture deficit during pegging halts peg penetration into the soil.

Commercial crops like sugarcane, cotton, and potato require high capital investment in irrigation infrastructure due to their long duration and high biomass production.

• Sugarcane (Saccharum officinarum): Consumes 1500–2500 mm of water across 15–20 irrigations. Critical periods include germination, tillering, grand growth phase (highest water demand), and maturity. Water stress during the grand growth period severely reduces cane yield and sugar recovery.
• Cotton (Gossypium hirsutum): Requires 700–1300 mm. Flowering and boll formation stages are critical. Irrigation must be managed carefully to prevent vegetative overgrowth and shedding of squares and bolls.
• Potato (Solanum tuberosum): Requires 500–700 mm. Tubers are sensitive to both drought and waterlogging. Regular light irrigations maintaining soil moisture at 50% available soil moisture (ASM) prevent tuber malformation and common scab.

To combat depleting groundwater tables and enhance water productivity, micro-irrigation systems and precision scheduling tools are vital.

• Drip Irrigation (Trickle Irrigation): Applies water drop by drop directly to the root zone through emitters. Achieves 90–95% water use efficiency, prevents weed growth, and enables fertigation.
• Sprinkler Irrigation: Simulates natural rainfall through overhead nozzles under pressure. Ideal for undulating topography and sandy soils where surface irrigation causes heavy percolation losses.
• Check Basin and Border Strip Methods: Traditional surface irrigation methods optimized with proper sizing to reduce tail-water runoff and deep percolation.
• Irrigation Scheduling Parameters: Utilizing IW/CPE ratio (Irrigation Water to Cumulative Pan Evaporation), typically set at 0.75 to 1.0 for optimal field crop scheduling.