Potatoes are a cool weather crop that require about 2.5 cm (1 in.) of water a week to produce the highest possible yield.

Two main reasons that potatoes are more sensitive to water stress than most other crops are:

  • a shallow root system: potatoes have a relatively shallow root system with most of the roots in the top 30 cm (12 in.) of soil
  • soil type: potatoes do well in sands and sandy loams, soils that have low to medium water-holding capacity

High yields of high-quality potatoes can only be achieved by maintaining high levels of available soil moisture throughout the growing season. Without regular rainfall, frequent irrigation is necessary. Soil moisture becomes critical when the available soil water drops below 60% to 65%. The impact of water stress will depend on the severity, timing and duration of moisture stress.

Potato yield loss in drought conditions

The table below shows the crop growth stages of potatoes and the amount of available water required for a high yield of good quality potatoes. Research in the United States has shown that yield losses will occur if available soil water drops below required levels for more than five days.

Growth stageSoil available water requirementYield losses if available water is below required levels
Growth stage 1: sprout development75% available soil waterShort periods of drought stress do not reduce yield.
Growth stage 2: vegetative growth75% available soil water5%
Growth stage 3: tuber initiation80% available soil water10%
Growth stage 4: tuber bulking90% available soil water40% to 60%

Highest demand for water. Adequate water is necessary for high yield. Dry conditions favour tuber malformations.
Growth stage 5: tuber maturation60% to 65% available soil waterWater deficit causes tuber dehydration.

If there is insufficient rainfall, irrigation is required to keep the available soil water in the root zone above the allowable depletion level. This ensures that the crop will not suffer water stress and will produce maximum yield.