Re-evaluation of P Requirements for Irrigated Potatoes

Study author(s): Carl Rosen, University of Minnesota
Growing season(s): 2020, 2021, 2022
Minnesota location(s):

Note: Complete reports with figures and tables are available for download below.

2020 Growing Season2021 Growing Season2022 Growing Season

WHAT IS THIS PROJECT ABOUT?

This research project investigates why potato plants often respond positively to extra phosphorus fertilizer, even when soil tests show that phosphorus levels are already high. Potato crops are notoriously inefficient at absorbing phosphorus from the soil. This inefficiency is believed to stem from their shallow, limited root systems, management practices like hilling that further restrict  rooting volume, or soil-borne diseases that damage roots. Additionally, soil practices such as fumigation can destroy beneficial soil fungi (mycorrhizae) that naturally help roots absorb nutrients. This study was designed to help growers understand how different management practices, soil treatments, and potato varieties affect phosphorus uptake so fertilizer applications can be optimized for better efficiency and profit.

KEY PROJECT GOALS & FARMER BENEFITS

  • Improve Fertilizer Efficiency and Cost: Helps farmers determine if applying phosphorus to high-testing soils actually pays off, especially when fertilizer prices are high.
  • Compare Variety Needs: Examines whether different cultivars (Ivory Russet vs. Russet Burbank) have different  nutrient demands.
  • Optimize Application Methods: Tests whether banding fertilizer near the seed row is more effective than broadcasting it across the whole field.
  • Evaluate Soil Health Treatments: Explores how soil fumigation affects crop nutrient intake and whether adding beneficial mycorrhizal fungal inoculants at planting improves root absorption.
  • Protect the Environment: Reduces unnecessary phosphorus applications and soil phosphorus build up, minimizing nutrient runoff into nearby water bodies while maintaining crop quality.

HOW THE STUDY wAS CONDUCTED

  • Field Testing Locations: The experiment was conducted over three years using experimental fields with high soil phosphorus levels and a slightly acidic to near neutral soil pH.
  • Fumigation vs. Non-Fumigation: Trial plots were split between soil treated with a fumigant (metam sodium/Vapam) to control soil-borne diseases and soil left unfumigated.
  • Variety Comparisons: Researchers planted two separate varieties—Ivory Russet (a determinate variety) and Russet Burbank (an indeterminate variety)—side-by-side.
  • Fertilizer Rates and Placement: Nine distinct phosphorus treatments were applied, ranging from 0 up to 450 lbs per acre of P2O5, using both preplant broadcast and at planting  precision banded placement methods (3 “ to the side and 2” below the tuber.
  • Biological Inoculation: Select plots were treated in-furrow at planting with a commercially available mycorrhizal inoculant to see if adding beneficial fungi improves root uptake in both fumigated and unfumigated soils.
Back To Top