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Secondary Nutrients are Critically Important

Potato growers spend appreciable time and effort carefully managing their fields’ nitrogen, phosphorus and potassium levels. Successful producers don’t stop there, however. They understand that secondary nutrients like magnesium, sulfur and calcium – though required in smaller amounts than nitrogen, phosphorus and potassium – are equally essential to plant growth.

As per Leibig’s Law of the Minimum, whichever nutrient is least available to plants will prove the limiting factor on crop growth. Potato growers should plan a nutrient management strategy that includes soil testing, crop scouting, nutrient tracking and mapping of in-field variability to best address all essential plant nutrients.

Sulfur is a primary component of plants’ essential amino acids and proteins. In a potato crop, it is necessary in a 1:15 ratio with nitrogen. Whereas producers used to be able to rely on plants absorbing sufficient sulfur from atmospheric deposits and organic matter in the soil, this is no longer the case. In fact, sulfur deficiency is becoming widespread in potato fields due to a combination of operational, technological and biological factors. Less sulfur is now available to crops because soil organic matter continues to decrease; producers are growing higher yielding, sulfur-hungry crops; there are lower industrial sulfur emissions to the atmosphere; and high sulfur containing fertilizers/pesticides have been replaced.

Magnesium is the central element that makes up chlorophyll, the pigment that allows plants to translate light into energy. Carbohydrates created through photosynthesis are first directed towards a plant’s leaf production. Only once sufficient energy goes into foliage will a potato plant start redirecting the energy towards initiating and bulking tubers. Therefore, a shortage in magnesium can significantly impact yield in an outwardly healthy looking plant.

The majority of North America’s potato growing acres are either low pH or high pH. Applying agricultural limestone is an effective way to increase the pH level in very acidic soils. Growers who opt to apply lime get the added benefit that lime is an excellent source of magnesium and calcium. Producers who choose to skip lime application, usually to counter diseases like common scab that are more severe in alkaline soil, need to prioritize monitoring and managing their fields’ magnesium and calcium requirements.

Potatoes require a constant and sufficient supply of phosphorus through late bulking. Many potato growers apply phosphorus before or at planting, expecting that it will remain available throughout the entire growing season. At a pH level of less than 6.0 (very acidic) or more than 7.2 (very alkaline), phosphorus becomes tied-up in soil, rendering it unavailable to plants. If potato plants face insufficient phosphorus supply, linear tuber growth during bulking will be suppressed. Keep in mind that, though slow-release fertilizer can offer season-long potato nutrition, its benefits will not be fully achieved if essential nutrients like sulfur and calcium are not available in sufficient supply.

Crop nutrition is a delicate balancing act between multiple variables that impact each other. Understanding crop nutrition and carefully managing it in-crop will pay significantly in plant health, crop quality and yield.

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