💧 Irrigation & Soil Water Balance

Drip (trickle) irrigation is the most efficient, delivering water directly to the root zone through emitters and achieving irrigation efficiencies of 90–95%. Sprinkler systems typically reach 70–85% efficiency, while surface flood irrigation is often below 50% due to evaporation, runoff, and deep percolation losses.

Evapotranspiration (ET) is the combined water loss from soil evaporation and plant transpiration. Reference ET (ET₀) is computed from weather data (temperature, humidity, wind, radiation) using the FAO Penman-Monteith equation. Crop ET is estimated as ET₀ times a crop coefficient (Kc) specific to the plant and growth stage. Irrigation scheduling replaces ET to maintain soil moisture in the optimal range.

Deficit irrigation intentionally applies less water than the full crop water requirement at certain growth stages, accepting a moderate yield reduction to achieve large water savings. Many crops tolerate mild stress during non-critical stages. For example, winter wheat can be under-irrigated at vegetative stages with minimal yield loss, saving 30–50% of irrigation water.

Sandy soils have high infiltration rates and low water-holding capacity, requiring frequent small irrigation events. Clay soils infiltrate slowly but hold more water, risking waterlogging if over-irrigated. Loam soils balance infiltration and retention and are ideal for most crops. Irrigation system design — emitter spacing, flow rate, cycle duration — must match the soil's hydraulic properties.

Irrigated agriculture produces roughly 40% of the world's food on 20% of cultivated land, and is essential for year-round production in arid and semi-arid regions. Without irrigation, global food production would fall dramatically and seasonal price volatility would increase. As aquifers deplete and rivers face growing demand, improving irrigation efficiency is critical for sustaining food supply under climate change.