Soil pH and potatoes: why the 5.0–6.0 range is not universal
Moderately acidic soil helps suppress common scab, but there is no single pH target for every farm — it is a trade-off between disease and nutrient availability.
Potato Nutrition series · Part 02 of 24 · All parts in order
Potatoes are often grown on moderately acidic soils because this helps reduce the risk of common scab caused by Streptomyces. But the claim that every farm needs exactly the same acidity is wrong. Cornell notes that common scab is controlled or strongly suppressed at a soil pH of about 5.2 or lower, and growers on susceptible varieties often aim for 5.0–5.2; yet in such acidic soil some nutrients become less available. There are also pathogens that cause “acid scab”.
In New Brunswick, a pH of about 5.5 is recommended for scab-susceptible round white varieties, while 5.5–6.0 is recommended for Russet types. This is an agronomic compromise between disease and nutrition, not a universal liming target. pH measured in water and pH in KCl are different measurements, and values cannot be compared without stating the method. Liming directly before potatoes can increase scab risk, so it is often moved to another crop in the rotation.
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Soil pH: the choice depends on variety, disease and nutrient availability
| Situation | Typical reference | Why |
|---|---|---|
| Scab-susceptible varieties (Cornell) | pH ≤ 5.2 | Suppresses common scab |
| Round white, scab-susceptible (New Brunswick) | about pH 5.5 | Compromise between scab and nutrition |
| Russet types (New Brunswick) | pH 5.5–6.0 | Better nutrient availability |
| Strongly acidic soils (Kenyan highlands) | Analyse, consider liming in rotation | N, P, K, S, B constraints |
Check local recommendations and the pH method (water vs KCl).
On excessively acidic fields, a strategy of simply “not liming” is also dangerous: nutrient uptake is suppressed and toxicities can increase. In the Kenyan highlands, research by CIP and partners recorded strongly acidic soils and constraints for N, P, K, S and B. Here a local programme to restore soil fertility is needed, not blind copying of Canadian scab-control schemes.
Geography and practical application
For Canada and the north-eastern US, scab history and variety matter most. For the acidic soils of Nakuru, Nyandarua and Meru (Kenya): acidity analysis, P constraints and possible liming within the rotation. On the calcareous soils of southern Russia, pH management requires an entirely different approach.
Regional notes
- Russia & Central Asia (Kazakhstan, Uzbekistan): southern Russia and irrigated Central Asia often have neutral-to-alkaline, sometimes calcareous soils, where the task is availability of P and micronutrients rather than liming.
- Latin America (Brazil, Andean countries): many tropical soils are acidic with aluminium constraints; liming decisions are made for the whole rotation, with scab risk weighed for susceptible varieties.
- Africa (Kenya, Nigeria, Zimbabwe, Zambia): acidic highland soils are widespread; liming and P supply are often the first yield limits, as Kenyan studies show.
- South-East Asia (Vietnam, Thailand, Philippines): highland soils are frequently acidic and leached; check pH method and aluminium before planning lime.
Agronomic guidance here is general practice; agree rates and timing with your agronomist.
Partner material: Uralchem products — conditional selection
No product is assigned automatically: the choice of a specific grade is made after analysis of soil, water and leaf/petiole tissue, and an assessment of the target market.
Where Uralchem supplies: Russia and the CIS, Latin America, Africa (through its distributor United Fertilizer Company Limited) and South-East Asia, where the company is developing distribution in Vietnam, Thailand and the Philippines. Availability of specific grades varies by country — check with the local distributor.
Not a rate recommendation — consult your agronomist.
Sources
- Cornell University, Potato Scab factsheet.
- New Brunswick Department of Agriculture, Potato soil management.
- Mugo et al. (2020), Soil fertility and potato nutrient status in Kenyan highlands, Scientific Reports.
- Mwakidoshi et al. (2026), Integrated nutrient management on acidic potato soils in Kenya, Food and Energy Security.
Partner data (Uralchem)
Potato Nutrition series · Part 02 of 24
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