SCIENCE · INVESTIGATE AND EXPLAIN

Interpret yield response without confusing ET with irrigation

Crop output depends on water availability and its timing, but also nutrients, temperature, salinity, pests and management. Evapotranspiration includes plant transpiration and evaporation; it can be supplied by rainfall, irrigation or stored soil water. Irrigation withdrawal additionally includes conveyance and return-flow pathways.

Learning outcome: Compare Ky 0.5 and 1.5 at ET ratio 0.8. Retain absolute yield and water productivity separately, then explain why equal seasonal ET need not guarantee equal yield across growth-stage timing.

Starting recap

Fix the useful service, lifecycle boundary and scenario; distinguish a conditional model result from an observed causal improvement.

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Try

At ET ratio 0.8 and Ky 1.25, relative yield is 0.75 and yield is 6 tonnes/ha. ET is 400 mm=4000 m³/ha; productivity is 6000/4000=1.5 kg/m³, versus potential 1.6.

Open the experiment

Predict

A higher kg/m³ water-productivity ratio necessarily means:

Your prediction and reason

Experiment

Compare Ky 0.5 and 1.5 at ET ratio 0.8. Retain absolute yield and water productivity separately, then explain why equal seasonal ET need not guarantee equal yield across growth-stage timing.

Compare relative yield and evapotranspiration response

Worked teaching model · synthetic values · Original potential yield 8 tonnes/ha and potential seasonal ET 500 mm=5000 m³/ha. Relative yield=1−Ky(1−ET ratio). Current ranges keep yield nonnegative. Seasonal linear approximation, no stage-specific, salinity, nutrient or heat interaction; ET is not irrigation withdrawal.

Actual / potential crop ET: 0.8 fraction Supplied yield-response factor Ky: 1.25 ratio

Reset keeps your prediction, captures and practice history.

Original synthetic system; units differ by row
Quantity	Value	Unit
Relative yield	0.75	fraction
Harvest yield	6	tonnes/ha
Seasonal evapotranspiration	400	mm
Seasonal consumed water	4000	m³/ha
Crop water productivity	1.5	kg/m³

Water productivity and absolute food output can move differently under stress.

Ky is a supplied conditional response coefficient, not a universal crop constant. ET includes rainfall and stored soil water; equating it to irrigation withdrawal would omit supply and return-flow pathways.

Predict, change one control, and save contrasting captures. Reconstruct the balance with units; then explain a process the ledger deliberately leaves out. Display precision is not measurement precision.

Water productivity and absolute food output can move differently under stress.

Observation to attach to a capture

Captures preserve recipes and replay their calculated results. They are synthetic model evidence, not physical measurements.

Understand

Define the useful service

Construct the comparable ledger

The original seasonal approximation uses relative yield loss=Ky×relative ET deficit. With potential yield 8 tonnes/ha and ET 500 mm, actual yield is 8[1−Ky(1−ET ratio)]. Ky is a supplied sensitivity coefficient. The supported range keeps predicted yield nonnegative and does not justify extrapolating the linear relation to severe stress outside that range.

Interpret the competing metrics

One millimetre over one hectare is 10 m³, so 500 mm is 5000 m³/ha. Water productivity divides kilograms of harvested product by consumed cubic metres. A larger ratio can coexist with lower absolute food output; neither quantity alone describes food security, profitability or ecosystem impact.

Challenge the boundary and scenario

Stage-specific stress can have different reproductive and growth effects, and a seasonal average can conceal that timing. The packet uses fictional coefficients, not a named crop forecast or an irrigation prescription. Independent yield and ET observations would be needed to estimate a response and test confounding by heat or nutrient stress.

Worked original packet

At ET ratio 0.8 and Ky 1.25, relative yield is 0.75 and yield is 6 tonnes/ha. ET is 400 mm=4000 m³/ha; productivity is 6000/4000=1.5 kg/m³, versus potential 1.6.

Investigation

Compare Ky 0.5 and 1.5 at ET ratio 0.8. Retain absolute yield and water productivity separately, then explain why equal seasonal ET need not guarantee equal yield across growth-stage timing.

Changed-case transfer

At ET ratio 0.6 and Ky 0.5, compute yield, consumed water and productivity; compare with unstressed output.

Feedback

Relative yield 0.8 gives 6.4 tonnes/ha; ET 300 mm=3000 m³/ha; productivity≈2.133 kg/m³. Productivity exceeds 1.6 while absolute output falls from 8 to 6.4 tonnes/ha.

Sources and evidence boundary

Original prose, numerical packets and exercises. Primary method/mechanism source, checked 30 October 2026. Supplied values are not measured operating data, universal coefficients or recommendations. No physical equipment work, chemical application, organism manipulation or water extraction is requested. Retain first reasoning and critique in the course workspace; public feedback is practice, not independent assessment.

Apply

Public practice checks a specific claim. It does not establish independent mastery.

At ET ratio 0.6 and Ky 0.5, compute yield, consumed water and productivity; compare with unstressed output.

Your explanation and limitations

Continue

Completion requires a saved prediction, at least one capture and a reflection. Presence checks do not grade your reasoning.

Skipping retains experiments and awards no mastery.

Previous: Track return flows before claiming real water savings Next: Audit nutrient efficiency denominators and missing pathways

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