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AMC, RAM and interval: FC 80%, PWP 35%

Short answer

Available moisture content (AMC) in root zone is 405 mm. Readily available moisture (RAM) is 283.5 mm. Depth of irrigation at field outlet is 354.4 mm, and irrigation interval is 56.7 days.

With following data: FC = 80%, PWP = 35%, root depth = 60 cm, soil density = 1.5 gm/cc, ETc = 5 mm/day, application efficiency = 80% and RAM = 70% AMC, where the abbreviations have usual meanings. (i) Calculate available moisture contents (ii) Calculate readily available moisture contents (iii) Calculate depth of irrigation at the outlet of the field (iv) Calculate irrigation interval.

Given: FC = 80%, PWP = 35%, Dr=60D_r = 60 cm =600= 600 mm, γd=1.5\gamma_d = 1.5, ETc=5ET_c = 5 mm/day, ηa=80%\eta_a = 80\%, RAM = 70% of AMC.

(i) Available moisture content

AMC=80−35100×1.5×600=405.00 mmAMC = \frac{80-35}{100}\times 1.5\times 600 = 405.00\ \text{mm}

(ii) Readily available moisture

RAM=0.70×405.00=283.50 mmRAM = 0.70\times 405.00 = 283.50\ \text{mm}

(iii) Depth of irrigation at the outlet of the field

d=RAMηa=283.500.80=354.375 mmd = \frac{RAM}{\eta_a} = \frac{283.50}{0.80} = 354.375\ \text{mm}

(iv) Irrigation interval

I=RAMETc=283.505=56.7 days≈56 daysI = \frac{RAM}{ET_c} = \frac{283.50}{5} = 56.7\ \text{days}\approx 56\ \text{days}

Answer: AMC = 405.00 mm; RAM = 283.50 mm; depth at outlet = 354.38 mm; interval = 56.7 days (about 56 days).

✓ Answer checked by Claude Opus 5.5 (high effort)

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