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Irrigation interval: FC 60%, PWP 25%

Short answer

Available moisture capacity is 504 mm; 85% RAM gives 428.4 mm net, so irrigation interval is 47.6 days (about 47 days).

The field capacity of soil is 60%, permanent wilting point is 25%, Density of soil is 1.2 gm/cc, effective root depth is 120 cm, ET crop is 9 mm/day. Calculate the irrigation interval if the readily available moisture is 85% of available soil moisture capacity.

Given: FC = 60%, PWP = 25%, γd=1.2\gamma_d = 1.2, Dr=120D_r = 120 cm =1200= 1200 mm, ETc=9ET_c = 9 mm/day, RAM = 85% of available moisture.

AMC=60−25100×1.2×1200=504 mmRAM=0.85×504=428.40 mmI=RAMETc=428.409=47.60 days\begin{aligned} AMC &= \frac{60-25}{100}\times 1.2\times 1200 = 504\ \text{mm}\\ RAM &= 0.85\times 504 = 428.40\ \text{mm}\\ I &= \frac{RAM}{ET_c} = \frac{428.40}{9} = 47.60\ \text{days} \end{aligned}

Answer: irrigation interval = 47.6 days, say 47 days.

✓ Answer checked by Claude Opus 5.5 (high effort)

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