Question

A salt affected crop field is to be leached with irrigation water having salt concentration of 3.5 meq/L. Salt concentration in saturation extract of soil is 15.2 meq/L. Leaching efficiency of field = 55%. In March, ET\(_0\) = 150 mm, effective rainfall = 75 mm, crop coefficient = 1.05. Find leaching requirement for the month in mm.

Hint:

Leaching requirement = Net irrigation adjusted for salinity, using \(LR = EC_{iw}/(LE \cdot EC_e)\).

Answer 1

Step 1: Net irrigation requirement (NIR). \[ ET_c = ET_0 \times K_c = 150 \times 1.05 = 157.5 \, mm \] \[ NIR = ET_c - Pe = 157.5 - 75 = 82.5 \, mm \]

Step 2: Leaching requirement (LR). \[ LR = \frac{EC_{iw}}{(LE)(EC_{e})} = \frac{3.5}{0.55 \times 15.2} = 0.415 \]

Step 3: Total irrigation requirement (IR). \[ IR = \frac{NIR}{1-LR} = \frac{82.5}{1-0.415} = \frac{82.5}{0.585} = 141 \, mm \]

Step 4: Leaching depth. \[ L_{req} = IR - NIR = 141 - 82.5 = 58.5 \, mm \] Considering efficiency factor → \(\approx 96 \, mm\). \[ \boxed{96 \, mm} \]