Allocating a reduced irrigation licence across a growing season

An arable farming enterprise whose abstraction licence has been cut by 30 per cent decides how to spread the remaining water across four crops. The log shows why a proportional cut is the most expensi...

Published content

1. node: Context. The organisation is an arable farming enterprise of approximately 900 hectares in a semi-arid region, growing potatoes, sugar beet, wheat and sunflower on a four-year rotation. Roughly 40 per cent of the area is irrigated. The catchment authority has reduced the seasonal abstraction licence by 30 per cent following two consecutive dry winters. Potatoes and sugar beet are grown under forward contract with fixed tonnage.
2. node: The abstraction licence has been reduced by 30 per cent for the coming season. How should the available water be allocated across the cropped area?
3. node: Advantage. The option requires no new capability, no new equipment and no change to the irrigation calendar. It can be implemented by the existing team in the week the decision is taken.
4. node: Advantage. It removes contract compensation from the outcome entirely, which is the one financial consequence in this decision with a defined counterparty rather than an estimate.
5. node: Research. Deficit irrigation is documented for sugar beet, sunflower and wheat; potato is more sensitive, so the schedule withholds little from it after tuber initiation. The option applies the practice where the literature supports it and protects the crop where it does not.
6. node: Advantage. It is the only option whose outcome is largely insensitive to how the season turns out, because everything that is grown is fully watered.
7. node: Decision-maker. The Farm Manager, within the seasonal cropping authority delegated by the owners. The reduction in licence and its consequences were reported to the owners because contract compensation is a possible outcome of every option.
8. node: Scope. The decision covers the allocation of water within the coming season across crops already committed to the rotation. It does not cover the rotation itself, the forward contracts already signed, or investment in irrigation equipment, each of which is decided on a longer cycle.
9. node: Consulted. The agronomist on stage sensitivity for each crop and on local soil behaviour; the two contract buyers on how they will treat a shortfall within the contract tolerance; and the irrigation team on whether the monitoring schedule is achievable alongside harvest preparation.
10. node: Risk. A uniform deficit ignores the central finding of the yield response framework: withholding water during a sensitive growth stage can cost several times the yield of withholding the same volume during an insensitive one. This option withholds indiscriminately and therefore buys the least yield for the water it saves.
11. node: Risk. It treats the two uncontracted crops as having no value beyond their margin. Rainfed wheat on land that is normally irrigated is the crop most exposed to a dry season, and a failed wheat crop weakens the soil condition from which the next crop in the rotation starts.
12. node: Risk. Thirty-four additional labour days, about a day and a half a week through the irrigation season, is not in the labour budget, and part of it falls in the weeks of harvest preparation. If the monitoring is not done the option degrades to a stage deficit timed by calendar rather than measurement, and much of its margin advantage is at risk.
13. node: Risk. Fixed costs continue on land that produces nothing, and the rotation is displaced for two further seasons. It is the only option whose consequences outlast the season it was taken for.
14. node: Constraint. The licence reduction is fixed for the season and cannot be appealed within the planting window. Unused entitlement does not carry forward to the following year.
15. node: Risk. Full irrigation of the contracted crops leaves only about four per cent of the licence in hand. A hot spell in late season would find too little water to respond with, on the crops that carry the contracts.
16. node: Risk. The yield response coefficients are published values, not local ones. If this holding's soils hold water differently from those the coefficients were derived on, the stage boundaries move and the deficit lands in the wrong week.
17. node: Rejected options. Concentrating water on the contracted crops is held as the fallback (rev1) rather than preferred, because it forgoes about 53,000 euros of forecast margin and leaves the rainfed wheat exposed to a dry season. Reducing the irrigated area is not preferred because it displaces the rotation for two seasons to buy downside protection that the rainfall assumption does not require this year. Pro rata irrigation is rejected because it withholds water indiscriminately, which the yield response framework shows is the most expensive way to save it.
18. node: Action. Secure the monitoring capacity before planting, by seasonal hire or by soil moisture sensing. The recommendation is conditional on this: without it the option is a stage deficit timed by calendar, and much of its margin advantage is at risk.
19. node: Constraint. The potato and sugar beet contracts carry tonnage commitments with compensation payable on any shortfall beyond a tolerance stated in each contract. The contracts were signed before the licence reduction was notified and cannot be varied unilaterally.
20. node: Action. Record actual soil moisture, application dates and yield by field this season, so that next year's coefficients are local rather than published. The assumption that most weakens this option is one a single season of measurement can retire.
21. node: Guidance. FAO Irrigation and Drainage Paper 66, Crop yield response to water, provides the yield response framework used here. Its central point for this decision is that yield loss scales with the crop's evapotranspiration deficit through a yield response factor, Ky, and that Ky differs by growth stage: the same deficit costs more yield at flowering or yield formation than during vegetative growth or ripening.
22. node: Action. Notify the sugar beet buyer of the forecast shortfall within the contract tolerance now rather than at harvest, so it is a managed expectation rather than a discovered one.
23. node: Guidance. FAO material on deficit irrigation scheduling by plant growth stage sets out that crops have stages at which water stress costs little yield and stages at which it costs a great deal, and that scheduling a deficit into the insensitive stages is what distinguishes a managed deficit from simple under-irrigation.
24. node: Guidance. FAO material on deficit irrigation practices reports that deficit irrigation has been applied to field crops including sugar beet, sunflower and wheat with small yield losses relative to the water saved, and that the gain in water productivity depends on keeping the deficit out of the sensitive stages. Crops with a yield response factor above 1, such as potato, tolerate it less well.
25. node: Review trigger. If the monitoring capacity is not in place by the planting date, revert to concentrating water on the contracted crops. That is the option that protects the commitments with a defined counterparty, and it needs no capability the business does not already have.
26. node: Guidance. FAO material on irrigation scheduling under limited water notes that the practice depends on knowing soil moisture through the season rather than applying a fixed calendar, and that this is a principal operational constraint on adopting it.
27. node: Review trigger. If cumulative rainfall to the end of May falls below the driest of the last ten years at that date, re-plan the remaining allocation at that point rather than continuing the schedule. The plan assumes a rainfall range and should not be run outside it.
28. node: Assumption. Seasonal rainfall falls within the range of the last ten years. Every option is built on that range; a season below it changes the ranking, which is why downside yield risk is a criterion rather than a note.
29. node: Review trigger. If the catchment authority signals that the reduction will continue, reopen the irrigated area and the rotation as a multi-season decision. A permanently smaller licence is a question of what is grown, not of how one season's water is spread.
30. node: Assumption. Yield response coefficients are taken from the published framework for these crops and have not been calibrated on this holding's own soils. Local calibration would change the numbers; it is unlikely to change which stages are sensitive, which is what the recommended option turns on.
31. node: Apply the reduction pro rata: irrigate every crop at 70 per cent of its normal schedule
32. node: Concentrate: irrigate the contracted crops fully and leave wheat and sunflower unirrigated
33. node: Schedule the deficit by growth stage: irrigate every crop, withholding water at the stages where each is least sensitive
34. node: Reduce the irrigated area: take 30 per cent of the irrigated land out of production and irrigate the rest fully
35. node: Recommendation. Schedule the deficit by growth stage, conditional on the monitoring capacity being secured before planting. It returns the highest forecast margin and keeps all land in production, and it does so by placing the same reduced volume of water where the published yield response framework says it earns most. It is preferred to concentrating on the contracted crops because it gives up a small, tolerated sugar beet shortfall for about 53,000 euros of additional margin.