High-Yield Potatoes Have High Nitrogen and Potassium Needs

Potatoes are grown in nearly every state in the U.S., with sales in excess of $3 billion. Yield, tuber size and specific gravity (dry-matter content) influence quality factors such as frying properties and flavor. Fertility management decisions can influence these as well as storage properties.

According to Dr. Rob Mikkelsen, the maturity class or growing-season length is a primary factor determining potato nutrient requirements.¹ Short-season varieties generally demand intensive nutrients during the vegetative and tuber initiation stages of growth. Maintaining a high photosynthetic rate in leaves is key to producing high tuber yields. However, excess nutrient applications may cause imbalance or over-stimulation of vegetative growth at the expense of tuber development.

Nutrient accumulation and removal by a 500 pounds-per-acre (lbs/a) yield of russet potatoes was determined by Dr. Don Horneck of Oregon State University. The total amount of nitrogen (353 pounds N) and potassium oxide (618 pounds K₂O) he found contained in the vines and tubers was very large. Nutrients removed from the field by the tubers was 214 lbs/a of N and 288 lbs/a of K₂O. Phosphorus (P₂O₅) requirements totaled 92 lbs/a of P₂O₅ with nearly three-quarters leaving the field in the tubers. Accumulation of magnesium (Mg) and sulfur (S) was 40 and 35 lbs/a, respectively. The high requirement for both N and K suggests that their application be timed with plant growth stage and needs to achieve optimum crop-use efficiency and nutrient effectiveness.

Plant requirements for phosphorus (P) increase until tuber set and early bulking. Late-growth need for P is met in part by translocation from top growth to the root system. Factors to consider in P nutrient management are the relatively shallow root system and cool soils at planting time. Since P moves little even in sandy soils, placement within the primary root zone is desirable. Growers select a particular P fertilizer source, such as monoammonium phosphate (MAP) or diammonium phosphate (DAP), by preference and compatibility with their equipment.

¹Better Crops, Vol. 90: No. 2, 2006

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