A correct balance between macronutrients and micronutrients is essential to obtain the best results possible from potatoes. A deficiency of any single nutrient is enough to limit crop yield and the availability of each nutrient needs to be related to the crop requirements. A review of nutrient uptake and offtake reveals which nutrients are required at which growth stages together with the role of each nutrient.
Liebig's law of the minimum, often simply called Liebig's law, states that growth is dictated not by total resources but by the scarest resource which becomes the limiting factor (Justus von Liebig, 1873). This is often depicted as Liebig's barrel where the individual staves in a barrel represent nutrients or other limiting factors.
Nutrient uptake varies throughout the season with the growth stage of the crop. While removal differs from field to field and depends on yield, potato crops can utilize 50% more potassium than nitrogen. A 38.5 t/ha (15.6 t/ac) crop can remove over 200 kg/ha (178 lb/ac) of potassium and 120 kg/ha (103lb/ac) of nitrogen. Both potassium and nitrogen are needed throughout vegetative growth, tuber formation and bulking.
Nitrogen is important for leaf and tuber growth. Like potassium, a lot of nitrogen is recycled from the leaf to the tuber during bulking.
Phosphate is also needed in relatively large quantities, particularly during early growth, to encourage rooting and tuber set, and then again during late season for bulking.
Potassium is particularly important for high yields but also for maintaining tuber integrity. "Luxury uptake" of potassium is typical in potatoes.
Sulphur is needed for all growth stages and is particularly important in reducing common scab.
A regular supply of calcium is critical to ensure stress-free leaf growth. Relatively high rates of calcium fertilizer are needed to achieve the small amounts in the tuber that are critical for crop quality.
Magnesium is more important at later stages of growth, particularly during bulking (See slide show), where it has a major role to play in maintaining tuber quality.
While much lower amounts of micronutrients are needed, the correct balance is essential for quality crop production.
Boron is needed in greatest quantities in order to ensure several key growth processes proceed unchecked. It is also important in optimizing calcium utilization.
While significant quantities of copper are used, deficiencies are rarely seen, with most soils providing adequate long-term supplies.
Manganese and zinc
Manganese and zinc are important for yield. Zinc plays a key role in N-assimilation and metabolism and starch formation.
Molybdenum can be important in low pH soils.