Water Use Efficiency & Crop per Drop

Water use efficiency (WUE), also called water productivity, is the yield you harvest per unit of water used: WUE = yield ÷ water used. It answers "how much crop per drop?" Expressed as kg per m³ or kg per mm, it lets you compare fields, seasons and practices on how productively they turn water into harvest rather than just on total yield.

Divide the crop yield by the water used over the season. If yield is in kilograms and water in cubic metres, WUE is kg/m³. The tool also reports kg per mm of water depth and its inverse — litres of water per kilogram of produce — which is an intuitive way to see how water-hungry a crop or practice is.

Water applied (m³) = depth (mm) × area (m²) ÷ 1000, because one millimetre of water spread over one square metre is one litre. So 100 mm over a hectare (10,000 m²) is 1,000 m³. You can enter water as a depth and area, or type a measured volume directly if you metered it.

It's the kilograms of harvested produce per cubic metre (1,000 litres) of water used. Higher is better. Typical values vary widely by crop and climate — cereals might be in the low single digits of kg/m³ while high-value vegetables differ — so the most useful comparison is against your own past seasons and neighbouring practices.

They are inverses of the same thing. kg/m³ tells you how much crop one cubic metre of water grows; litres per kg tells you how much water it took to grow one kilogram of produce. The L/kg figure is handy for water-footprint conversations, while kg/m³ is the usual agronomic productivity measure.

Lift WUE by cutting losses rather than just applying more water: switch to drip and use mulch to reduce evaporation, apply deficit irrigation at growth stages that are less sensitive to water stress, and match the variety and agronomy to the water you actually have. Healthy soil, weed control and good nutrition all help each drop produce more.

Deficit irrigation deliberately applies less water than full crop demand, concentrating the savings at stages where the crop tolerates mild stress with little yield loss, while keeping water up at sensitive stages like flowering and grain or fruit fill. Done well it can raise water productivity (kg/m³) even if total yield dips slightly.

Be consistent and compare like with like. You can compute WUE on irrigation water only (useful for judging the irrigation system) or on total water including effective rainfall (useful for overall crop water productivity). Just don't mix the two between fields or seasons, or the comparison will mislead you.

Yes. Enter yield in your preferred mass unit and water as a depth over an area or as a measured volume, and the tool reports kg/m³, kg/mm and L/kg. It works for cereals, vegetables, fruit and fodder — the productivity ratio is universal, only the typical values differ between crops.

They're as accurate as your inputs. Metered water and weighed yield give reliable productivity; estimated depths and eyeballed yields give ballpark figures. Use WUE to compare and steer — track it across seasons and treatments to see whether a change in irrigation or agronomy is genuinely producing more crop per drop.