b'TATER TALES Impact of Soil Moisture Stress on Potato Yield and QualitySoil moisture levels can have a huge effect on how your potato yield and quality.BECAUSE OF ITS shallow root system, the potatospecific gravity and increase the amount of jelly-end rot. crop is sensitive to drought. High yields of high- Water stress during bulking disrupts tuber growth quality potatoes can only be achieved by maintainingby reducing or stopping tuber expansion. When tuber adequate levels of available soil moisture throughoutgrowth resumes after rain or irrigation, the result the growing season. Without regular rainfall, frequentis misshapen tubers with cracks, pointed ends and irrigation is necessary.knobs. Water stress during bulking affects total yield Climate change will alter rainfall patterns andmore than quality. temperature, which will affect potato growth as wellTuber bulking slows down for maturation and soil as the incidence of diseases and pests. Drought stressmoisture can be reduced. Excessive irrigation will EUGENIA BANKS,has a tremendous impact on potato production andcause soft rot, Pythium leak and enlarged lenticels.potato specialistits impact depends on the severity and duration of theMechanical damage at harvest is affected by soil with the Ontario Potato Board stress and on the crop growth stage as well.water content. Dehydrated tubers are more susceptibleThe table below shows the growth stages and theto blackspot bruising. amount of available water required for a high yield ofAfter a period of moisture stress, potatoes need time high-quality potatoes. Soil moisture should be aboveto recover some or all their physiological functions. 70 per cent for all stagesstress becomes criticalConsequently, the effect on tuber yield may be when the available soil water drops below 65 per cent considerable. Research has shown that plants do not Research in the United States has shown yield lossesrecover fully after severe moisture stress for seven days. will occur if available soil water drops below requiredThere are few management strategies for dealing levels for more than five days. with water shortages other than irrigation.The first response of potatoes to water stress is the1.Increasing soil organic matter to three to four per closure of leaf stomata, the small pores that controlcent mitigates moisture stress by improving water-gas exchange between internal leaf cells and theholding capacity. Manure and cover crops help environment. This is a defense against further waterincrease the organic matter in soils. loss, but it also restricts the diffusion of carbon dioxide2. Pick varieties that develop a large canopy rapidly into the leaf. This slows photosynthesis, reducing theto shade the soil and reduce water loss. This isnt production of the sugars needed for tuber growth,always possible given the demands of the market.which lowers yield and quality. 3.Good calcium nutrition is important to reduce the Water deficits at tuber initiation reduce tuber setimpact of stress, not just water stress.and can increase the proportion of rough, misshapenAs always, Mother Nature is in charge; growers tubers. Early-season water stress can also reduceshould hope for the best but prepare for the worst. Estimated Potato Yield Losses Caused by Soil Moisture StressLosses depend on how low the available soil moisture drops below requirements.Growth Stage Available Soil Moisture Yield Losses if Available Soil Moisture Requirements Levels are Below Required LevelsGrowth Stage I 75-85% Short periods of drought stress do not Sprout Development reduce yieldGrowth Stage II 75-85% 5%Vegetative GrowthGrowth Stage III 80-90% 10%Tuber InitiationGrowth Stage IV 90% 40-60%Tuber BulkingGrowth Stage V 70-75% Water deficit causes tuber Tuber Maturation dehydration SPUDSMART.COM Spring 202251'