the salt tolerance of the crops to be grown. From figure 1 it is seen that 800 mm of water (or 8000 m3/ha) is required to bring the soil salinity down to 60% of its original value in the soil layer at 40 to 60 cm depth. When the salinity must be less than 60%, extrapolation of the leaching curve, the use of a leaching equation (see below) or a leaching model like SaltMod is necessary to obtain a reliable estimate of the additional leaching requirement. The annual amount of percolation water (i.e. the extra amount of irrigation water on top of the crop consumptive use) required to conserve an acceptable salt balance of the soil in accordance with the salt tolerance of the crops to be grown. The ratio FL = Perc/Irr, where Perc = amount of required percolation water, and Irr = total amount of irrigation water, is called leaching fraction, see also below. Leaching equation The downward limb of the leaching curves, as in figure 3, can be described with the leaching equation: Ct = Ci + (Co - Ci) exp (-EL.T.Qp/Ws) where C = salt concentration, Ct = C in the soil at time T, Co = C in the soil at time T=0, Ci = C of the irrigation water, EL = leaching efficiency, Qp = average percolation rate through the soil, and Ws = water stored in the soil at field saturation. Leaching fraction To conserve an acceptable salt balance of the soil in accordance with the salt tolerance of the crops to be grown, the leaching fraction must be at least: FL = Ci/Cs where Ci = salt concentration of the irrigation water, and Cs is the acceptable salt concentration of the soil moisture at field capacity in accordance with the salt tolerance of the crops to be grown. References External links Articles on soil salinity: Download leaching model : Download SaltMod from: Salt and water balances: Salt tolerance of crops: Software for salinity models: Drainage Soil Soil science Agricultural soil science Environmental soil science Land management Land reclamation Water management