Salinity Management Calculator

It's the fraction of the water you apply that must pass all the way through and below the root zone as drainage, rather than being taken up by the crop or evaporated. The calculator uses that fraction to inflate your gross irrigation need — dividing it by (1 − leaching requirement) — so the reported "total water with leaching" and "extra leaching water" outputs tell you exactly how much more water to apply beyond crop ET to keep salts from building up in the root zone.

The calculator adjusts the crop's base EC threshold upward using adjustedEce = threshold + (yield loss % × threshold × 0.12), reflecting that salt tolerance is a sliding scale rather than a hard cutoff — each percentage point of yield you're willing to sacrifice relaxes the threshold by roughly 12% of its base value. A higher effective threshold reduces the calculated leaching requirement, since the LR formula's denominator (5 × threshold − irrigation water EC) grows.

SAR (Sodium Adsorption Ratio) and salinity hazard measure two different risks from the same water. Salinity hazard, driven by EC, is about total dissolved salt reducing the crop's ability to take up water. SAR is about sodium specifically displacing calcium and magnesium in the soil, which can degrade soil structure and reduce infiltration — a water sample can be low in overall salinity but still have a high sodium hazard, so the two ratings are computed and reported independently using their own USDA threshold scales.

It's a simplified mass-balance approximation (irrigation water EC divided by the leaching fraction) that assumes complete mixing and steady-state conditions in the soil profile. Real soils rarely reach a perfectly mixed steady state, especially right after a leaching event, so treat the drain-water EC figure as a planning-level estimate rather than a prediction of what a specific drainage sample would measure.