GATE 2023 AG – Question 59
Irrigation water salt concentration is 3.5 meq/L and soil saturation-extract concentration15.2 meq/L. Leaching efficiency55%. March reference ET150 mm, effective rainfall75 mm, Kc1.05. Find monthly leaching requirement in mm, to two decimals.
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Correct answer: 19.50 to 19.55
Explanation
Crop ET is $ET_c=1.05(150)=157.5$ mm, so net irrigation deficit is 82.5 mm. The keyed calculation uses leaching fraction $LR=C_i/(2C_e-C_i)=3.5/(30.4-3.5)=.1301115$. Correcting the net leaching depth for efficiency gives $D_L=82.5(LR)/.55=\mathbf{19.52}$ mm. The factor2 is the empirical drainage-water/saturation-extract concentration convention implicit in this formula; a different salinity/leaching model would give a different depth, so that convention is made explicit.