Late-season water management in potato crops

An adequate water management programme can improve quality and yield of potato crops. Find out how late irrigation can affect your crops and read our 5-step guide to improving your late-season water management programme.

How late irrigation can affect your potato crops

Late-season water management, as the crop begins to senesce, is the essential final phase in an efficient irrigation regime.

Late irrigation can help reduce bruising, but only where the crop is actively growing
Water, combined with nitrogen management, plays an important role in skinset

Reducing bruising susceptibility

Yield, bruising susceptibility and secondary growth can all be affected at this time. The objective late in the season is to keep the tubers turgid, maintain full yield potential and provide some insurance against wet weather late in the season. Crops allowed to accumulate high SMDs (Soil Moisture Deficit) prior to defoliation can cause tubers to become dehydrated and increase the risk of bruising.

How late irrigation can affect skinset

Correct nitrogen management should result in late-season irrigation having little effect but, for crops defoliated prior to active senescence, water can still be taken up and this may slow skinset.

Overwatering issues

If soils are too wet, rotting diseases, lenticel eruption and reduced dry matter accumulation can result. However, switching off irrigation leaving the crop to survive on soil reserves alone during dry periods can be equally detrimental. You should, therefore, focus on monitoring SMDs leading up to desiccation, rather than irrigating immediately prior to desiccation and/or lifting.

5 steps to improving your late-season water management

Continue monitoring SMDs leading up to desiccation and harvest
Maintain moderate SMDs during August, close to the limiting SMD for yield (eg 35mm for sand, 45mm for sandy loams, 55mm for silty loams)
After crops have senesced to less than 50 per cent ground cover, there is little benefit (in yield or quality) in continuing irrigation. However, if senescence is variable in the field, best practice would be to irrigate the whole field to reduce the risk of bruising and accept some over-watering where the crop is dead
To reduce bruising, avoid desiccating or flailing following a hot or dry period unless soil has been maintained in a wet status. Following very hot days, it is better to defoliate on the following morning
Rapid defoliation (mechanical) of actively growing canopies can result in significantly increasing bruising, particularly if the crop has been previously irrigated and then allowed to dry out prior to defoliation