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Irrigation interval: FC 28%, PWP 13%

Short answer

Available moisture = (28–13)/100 × 1.3 × 700 = 136.5 mm. Interval = 136.5 / 12 = 11.38 days; irrigate every 11 days.

After how many days will supply water to soil in order to ensure sufficient irrigation of the given crop if, (i) Field capacity of the soil = 28%, (ii) Permanent wilting point = 13%, (iii) Dry density of soil = 1.3 gm/cc, (iv) Effective depth of root zone = 70 cm, (v) Daily consumptive use of water for the given crop = 12 mm.

Given: FC = 28%, PWP = 13%, γd=1.3\gamma_d = 1.3 g/cc, root zone depth Dr=70D_r = 70 cm =700= 700 mm, ETc=12ET_c = 12 mm/day.

Step 1: Available moisture depth

d=FC−PWP100×γdγw×Dr=28−13100×1.3×700=136.50 mm\begin{aligned} d &= \frac{FC-PWP}{100}\times\frac{\gamma_d}{\gamma_w}\times D_r\\ &= \frac{28-13}{100}\times 1.3\times 700 = 136.50\ \text{mm} \end{aligned}

Step 2: Irrigation interval

I=dETc=136.5012=11.38 daysI = \frac{d}{ET_c} = \frac{136.50}{12} = 11.38\ \text{days}

Answer: irrigate after about 11.4 days, i.e. every 11 days (rounded down so the crop does not suffer stress).

✓ Answer checked by Claude Opus 5.5 (high effort)

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