Africa Estate Farm Tools

Water & irrigation: what can it irrigate, and what does pumping cost?

Two questions every irrigation farm raises. Crop water need: what the crop takes by FAO 56, what the rain gives back, what the system must apply and how many hectares the registered water covers. Pumping cost: the kilowatts a borehole or river pump draws, the hours it runs and what a season costs at your tariff.

1. The crop (FAO 56)

Kc and stage lengths fill in from FAO 56 Tables 11 and 12 (Spain); change any of them.
FAO 56: 0,35 if harvested dry

2. The climate of the farm, month by month

Reference evapotranspiration (ETo, mm per month) from FAO CLIMWAT 2.0, SAPWAT 4 or your weather station; rainfall (mm per month) from your rain gauge or the rainfall tool. The tool ships no regional values: a station average is not this farm.

JanFebMarAprMayJunJulAugSepOctNovDec
ETo mm
Rain mm

3. The system and the water

FAO Manual 4 indicative values; type 85 if your pivot reaches it.
The volume on the water use entitlement (WARMS) or the scheme allocation.
Assumptions used
  • ETc = Kc x ETo per day on the FAO 56 curve; crop coefficients and stage lengths: FAO Irrigation and Drainage Paper 56, Allen et al. (1998), Tables 11 and 12.
  • Effective rainfall: USDA Soil Conservation Service method, as used in FAO CROPWAT 8.0: Peff = P x (125 - 0,2 P) / 125 up to 250 mm a month, 125 + 0,1 P above, pro rata over the season days in the month.
  • Application efficiency: FAO Irrigation Water Management Training Manual No. 4 (1989), indicative field application efficiencies.
  • Pump power = Q x H x 9,81 / (3 600 x efficiency); efficiency 0.66: Nebraska Pumping Plant Performance Criteria (pump 75%, electric motor 88%), as cited by K-State Research and Extension and Oklahoma State University; USDA NRCS Standard 533.
  • Tariff: Eskom Tariffs and Charges Booklet 2026/27 (Landrate, Ruraflex), effective 1 April 2026; typed from your account, never assumed.

The answer

Choose the crop and type the monthly ETo (and rainfall) for the farm to see its water need.

Crop need (ETc), mm
0
Effective rain, mm
0
To apply (gross), mm
0
m³ per hectare
0
Hectares your water covers
0
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What this does not tell you

  • A water need is not a water authorisation: the National Water Act 36 of 1998 decides what you may take; read the water rights guide.
  • ETo and rainfall are what you typed; a station average is not this farm.
  • Kc values are FAO 56's sub-humid standard; a hot, dry, windy site runs higher at mid-season (FAO 56 equation 62).
  • A pump test gives your real efficiency; 0,66 is a well-running average system.

Sources

Estimate, not advice. Confirm every figure with your bank, attorney and tax practitioner before a decision.