ISSUE #396

396 - Use of Starter Fertilizer to Reduce Phosphorus Costs

3-12-01

Phosphorus is a primary plant nutrient essential for optimum plant growth. Serious yield reductions occur when insufficient P is available for crop growth. P fertilizer applications are based on soil test levels from the surface 6” of the soil and a crop yield goal. The P test indicates the very small portion of total soil P in solution that is readily available to plants. Figure one indicates P in soil is continually moving between different available or exchangeable pools in the soil.

Figure 1

396.1

As plants use P from the soil solution it’s replenished from the exchangeable P pool in the soil. Soil test levels don’t necessarily reflect how much can become available to a crop from the soil reservoirs of organic and exchangeable phosphorus.

Some growers recently reported that use of only starter fertilizer was able to fully meet sugarbeet crop P requirements for growth. Recent University of MN research by Smith and Sims supports these claims, Figure 2.

396.2

This University of Minnesota research by Dr. Al Sims and Dr. Larry Smith shows: 

  • 10-34-0 at 3 GPA gave maximum root yields.
  • 45 to 60 lbs./acre of 18-46-0 were required to maximize yields.
  • Using only starter P fertilizer will reduce fertilizer costs by $5 to $10 per acre for many fields.
  • The soil test at the research site was 5 ppm.

How can starter 10-34-0 placed in the seed furrow give this response?

  • Three gallons of 10-34-0 contains over 11 lbs. of P.
  • Starter P is essentially “band applied.”
  • Root uptake of band applied P is more efficient.

P Deficiency Symptoms:

  • Stunted seedling growth
  • Upright cotyledon or early leaves
  • Somewhat cupped leaves
  • Purplish leaf margins

396.3

Tips for effective use of starter fertilizer for sugarbeets:

  • NEVER exceed 5 lb./acre of N plus K in the starter or excessive stand loss may occur.
  • Smith and Sims used 3 GPA of starter plus 3 GPA of water for better application uniformity and less risk of stand loss.
  • Phosphorus is the key nutrient needed not N or K.
  • Stand loss risk is greater on dry, lighter textured soils, with rates over 3 lb./acre N and K combined.

For more detailed P management information for sugarbeet production see Ag Notes #385, August 28, 2000. Detailed discussion of University of MN starter fertilizer research is available in the 1999 and 2000 Sugarbeet Research and Extension Reports.