Leaching Fraction

Salt accumulation in irrigated soils is unavoidable because every irrigation event delivers dissolved salts but only the water evaporates or transpires — the salts stay behind. Without periodic leaching, EC in the root zone rises until yields collapse. The leaching fraction tells you how much *extra* water (beyond crop ETc) you must apply so the salt stays diluted enough not to harm the next crop.

Worked example for olive (ECe threshold 4.0 dS/m) irrigated with EC 4.0 dS/m water: LF = 4 / (5 × 4 − 4) = 0.25. Gross irrigation = ETc × (1 + 0.25) — for an ETc of 5 mm/day during peak season, gross = 6.25 mm/day, with 1.25 mm draining as leachate. For barley (threshold 8.0) on the same water: LF = 4 / (5 × 8 − 4) = 0.11 — a much smaller penalty, demonstrating why salt-tolerant crops are economically critical in saline regions. (Date palm shares olive's ~4.0 dS/m threshold but stays productive far above it with adequate leaching, which is why it thrives in saline oases like Siwa.)

Delivery strategy matters: under sprinkler or flood, leaching is naturally distributed because each event soaks the whole root zone. Under drip, salts accumulate at the wetting-front edge between emitters, so periodic deep watering (deficit irrigation cycle followed by a heavy leaching set every 2–4 weeks) outperforms continuous drip during high-EC seasons. Acid-flush of drip lines monthly above EC 2.0 dS/m prevents bicarbonate-precipitation clogging that otherwise reduces emitter uniformity and concentrates salts at remaining functional outlets. WiseYield's irrigation advisor reads the latest water-EC sample, computes the per-crop LF, increases the recommended gross irrigation accordingly, and surfaces a salt-clogging tip when EC exceeds the drip-clogging threshold.