How this calculation works
Irrigation water can carry salts into the root zone while crop water use leaves much of that salt behind. A conventional steady leaching relation estimates the fraction of infiltrated water allocated to drainage under specified salinity assumptions.
LR = ECw/(5ECe − ECw); infiltrated depth = net crop need/(1 − LR); gross depth = infiltrated depth/delivery efficiencyA worked example
At ECw one and ECe four dS/m, the conventional fraction is 1/(20 − 1), about 5.263 percent. A 100 mm crop-water need therefore requires about 105.556 mm infiltrated in this balance. The extra 5.556 mm is the modeled leaching component. At eighty-percent delivery efficiency, gross application is about 131.944 mm. That is a scenario result, not an irrigation prescription.
Good to know
Conventional steady surface/sprinkler relation only; no transient salt transport, crop-yield guarantee, drip-specific adjustment or chemical hazard assessment. Targets, drainage and field suitability need qualified assessment. Do not use an arbitrary conductivity target to generate a field watering instruction.
Reference: USGS — conventional leaching relation (opens in a new tab) ↗
What the model answers
Irrigation water can carry salts into the root zone while crop water use leaves much of that salt behind. A conventional steady leaching relation estimates the fraction of infiltrated water allocated to drainage under specified salinity assumptions.
This page exposes that algebra without selecting a crop tolerance or claiming to simulate a soil profile. The target conductivity and applicability of the relation must be established outside the calculator.
The Crop water ET0 depletion schedule calculator supplies a separate time-based crop-water balance. Its depletion ledger does not itself calculate steady salt leaching or validate an ECe target.
Measure and enter consistently
ECw describes irrigation-water conductivity. ECe describes saturation-extract soil conductivity; it is not automatically the same as a probe reading or a different soil-to-water extraction ratio. Both use dS/m here.
Delivery efficiency describes water lost before serving the intended root-zone balance. Intentional leaching is kept separate so it is not automatically counted twice as an application loss. The crop-water requirement is entered before adding that leaching allowance.
Interpret the result
The formula requires a positive denominator and a leaching fraction below one. Combinations outside that range are rejected because the modeled infiltrated depth would become nonphysical or unbounded.
Even a feasible algebraic fraction does not establish drainage capacity, environmental acceptability or crop response. Rainfall, chemical composition, soil variability and localized drip wetting can require a different assessment.
Work through the numbers
At ECw one and ECe four dS/m, the conventional fraction is 1/(20 − 1), about 5.263 percent. A 100 mm crop-water need therefore requires about 105.556 mm infiltrated in this balance.
The extra 5.556 mm is the modeled leaching component. At eighty-percent delivery efficiency, gross application is about 131.944 mm. That is a scenario result, not an irrigation prescription.
Where this model stops
Conventional steady surface/sprinkler relation only; no transient salt transport, crop-yield guarantee, drip-specific adjustment or chemical hazard assessment.
Targets, drainage and field suitability need qualified assessment. Do not use an arbitrary conductivity target to generate a field watering instruction.
A few questions, answered
Can I enter any soil conductivity reading as ECe?
No. The relation uses saturation-extract conductivity, so measurement conventions must match.
Is leaching just inefficient delivery?
No. Intentional root-zone drainage and losses before effective delivery are separate terms in this model.