Irrigated potatoes

Key points

Factors affecting N rate:

• Know the type of potato you're growing
  • Determinate varieties tend to use less nitrogen
  • Indeterminate varieties require more N
• Market class N requirements
  • Fresh market (smaller) tubers require less N
  • Processing (large) tubers requires more N
  • Seed potatoes require less N
• Know your yield goal (depends on market class, cultivar type and soil organic matter)
• Projected killing date (primarily for fresh market)
• Nitrogen credits (ex. previous legume crop, etc. and irrigation water if nitrate > 10 ppm)

Application timing

• N demand is high in tuberization stage (Growth stage III, 50-70 days after planting)
• N demand moderate to high during bulking (Growth stage IV)
  • Any N applied after mid-tuber bulking will not be used efficiently
• No fall N is recommended on sandy soils
• Starter: 40 - 60 lb N/acre depending on variety
• Hilling: N should be incorporated
• Majority of soluble N should be applied 10 - 50 days after emergence

Nitrogen source

• No nitrate-N in starter
• ESN good for late season varieties when applied at emergence
• ESN not good for early season varieties

Water management

• Do not over irrigate - can lead to nitrate leaching
• When possible, plant a cover crop after potato harvest