GATE 2023 AG – Question 42
Soil field capacity/wilting moisture are.21/.09 cm³/cm³,root depth .90 m and MAD50%. January/February/March reference ET is 11/12/14 mm/day, effective rain8/25/27 mm/month, and Kc.80/1.10/1.15. Find average irrigation interval Jan1–Mar31 in days.
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Correct answer: (B) 6
Explanation
Available storage is $(.21-.09)(900)=108$ mm, and readily available storage at 50% MAD is 54 mm. For a 90-day nonleap season, crop ET is $31(11)(.8)+28(12)(1.1)+31(14)(1.15)=1141.5$ mm. Effective rain totals60 mm; average net use is 1081.5/90=12.0167 mm/day. Interval is 54/12.0167=4.49 days. The official choice is **6 days, B**,which does not follow from those stated monthly data under this standard storage/ET balance. Grading remains official; the mismatch is disclosed rather than changing crop coefficients.