MSc Agribusiness & Water

Faculty of Agriculture and Environmental Sciences · CDU-AGR-AGW-900 · MSc · v1.0.0

Crop water and the money it makes: daily reference evapotranspiration by FAO-56 Penman–Monteith, the net and gross irrigation requirement of a crop over a period, the physical and economic productivity of the water applied, and the gross margin, break-even yield and break-even price of an enterprise.

Lineage

Conquest Designer University, 2026 — authored from the brief and FAO Irrigation and Drainage Papers 24, 56 and 66; no prior institution is claimed

Final research project

The value of a cubic metre: reference evapotranspiration, irrigation need, water productivity and the farm gross margin

Syllabus

Reference evapotranspiration: radiation, temperature, humidity, wind, the psychrometric constant (FAO-56 ch. 2–4)
Crop water requirement: Kc, effective rainfall, application efficiency (FAO-56 ch. 6; FAO-24)
Water productivity: kg per m³, revenue and margin per m³ (FAO-66)
Enterprise budgets: revenue, variable costs, gross margin, break-even yield and price

Reference

FAO-56 ET0: [0.408·Δ·(Rn − G) + γ·(900 ÷ (T + 273))·u2·(es − ea)] ÷ [Δ + γ·(1 + 0.34·u2)] (eq. 6)
Vapour pressure: e°(T) = 0.6108·exp(17.27T ÷ (T + 237.3)); ea = [e°(Tmin)·RHmax + e°(Tmax)·RHmin] ÷ 200 (eq. 17)
Psychrometric constant: γ = 0.665 × 10⁻³ × P; P = 101.3·((293 − 0.0065z) ÷ 293)^5.26
Irrigation requirement: ETc = Kc·ET0; net = ETc − effective rain; gross = net ÷ efficiency; 1 mm on 1 ha = 10 m³
Gross margin: yield × price − variable costs

Units

Reference evapotranspiration (FAO-56 Penman–Monteith) · Net and gross irrigation requirement · Physical and economic water productivity · Enterprise gross margin and break-evens

Role when narrated: You are an agricultural water engineer and agribusiness adviser speaking to a grower. Weather, soil and water first; then the calculation; then the next affordable decision about water and the crop.

Reference evapotranspiration (FAO-56 Penman–Monteith) · et0_penman_monteith

Try with the example

How much water does the reference grass surface lose on this day, in mm?

Reference: Allen et al. (1998) FAO-56 eq. 6 (daily ET0), eq. 7–8 (P, γ), eq. 11–13 (es, Δ), eq. 17 (ea from RHmax and RHmin); worked Example 18 (Brussels, 6 July) gives 3.9 mm/day

Returns

et0: Reference evapotranspiration, mm/day
vapourPressureDeficit: es − ea, kPa
slope: Δ, kPa/°C
psychrometricConstant: γ, kPa/°C

The example

{
  "tMax": 21.5,
  "tMin": 12.3,
  "rhMax": 84,
  "rhMin": 63,
  "windSpeed2m": 2.078,
  "netRadiation": 13.28,
  "soilHeatFlux": 0,
  "altitude": 100
}

Agents: POST /faculty/msc-agribusiness--water/et0_penman_monteith with JSON {pan, …inputs} and the x-402-payment header. Manifest.

Net and gross irrigation requirement · irrigation_requirement

Example filled in — consult below

Over this period, how much water does the crop need from irrigation, at the field and at the source?

Reference: FAO-56 ch. 6 (single crop coefficient: ETc = Kc·ET0); FAO-24 (application efficiency); 1 mm over 1 ha = 10 m³

Returns

cropEt: ETc over the period, mm
netRequirement: ETc − effective rain (not below 0), mm
grossRequirement: Net ÷ efficiency, mm
volumePerHectare: Gross × 10, m³/ha

The example

{
  "et0": 5.2,
  "cropCoefficient": 1.15,
  "days": 30,
  "effectiveRainfall": 40,
  "applicationEfficiency": 0.75
}

Agents: POST /faculty/msc-agribusiness--water/irrigation_requirement with JSON {pan, …inputs} and the x-402-payment header. Manifest.

Physical and economic water productivity · water_productivity

Try with the example

How much crop, revenue and margin does each cubic metre of water produce?

Reference: FAO-66 (Steduto et al. 2012): crop water productivity in kg per m³ of water consumed; economic productivity as value per m³

Returns

kgPerM3: Yield ÷ water
revenuePerM3: Revenue ÷ water
grossMarginPerM3: (Revenue − variable costs) ÷ water

The example

{
  "yieldKgPerHa": 9000,
  "waterM3PerHa": 6000,
  "pricePerKg": 3.2,
  "variableCostPerHa": 18000
}

Agents: POST /faculty/msc-agribusiness--water/water_productivity with JSON {pan, …inputs} and the x-402-payment header. Manifest.

Enterprise gross margin and break-evens · gross_margin

Try with the example

What gross margin does this enterprise earn, and at what yield or price does it only just cover its variable costs?

Reference: Farm-management enterprise budgeting (gross margin = output value − variable costs); Kay, Edwards & Duffy, Farm Management

Returns

revenuePerHa: Yield × price
grossMarginPerHa: Revenue − variable costs
totalGrossMargin: Per-ha margin × hectares
breakevenYield: Variable costs ÷ price
breakevenPrice: Variable costs ÷ yield

The example

{
  "yieldPerHa": 6.5,
  "pricePerUnit": 4200,
  "variableCostPerHa": 19500,
  "hectares": 120
}

Agents: POST /faculty/msc-agribusiness--water/gross_margin with JSON {pan, …inputs} and the x-402-payment header. Manifest.