385 - Phosphorus Management Strategies 

8-30-00

Help Achieve Fertility Gold Standard Performance

Shareholders focus on Nitrogen management, relatively high Phosphorus soil test values, and lack of an obvious response to Phosphorus fertilizer have diverted shareholder attention from Phosphorus management recently. However inadequate available soil residual or added fertilizer Phosphorus has reduced sugarbeet yields on numerous fields. Phosphorus deficiency symptoms and associated yield reduction has become more common in recent years. On some light textured soils yields have been lower than expected for 10 years or more. Yields may also be reduced on heavy textured soils at times.

Phosphorus Deficiency Symptoms

Phosphorus deficiency symptoms in sugarbeet seedlings include:

• Stunted plant growth in the spring
• Upright and somewhat cupped leaves
• Purple color on leaf margins

Symptoms begin to appear a few days after sugarbeet plants emerge. Plants have remained stunted for one to two months before resuming growth and "catching" up to unaffected parts of the field. Slowed growth for short periods of time often doesn’t result in yield loss, but beet stunting for 4 to 6 or up to 8 weeks can result in yield reductions. Sugar/acre declined by 2800 lbs./acre in 1998 studies at the Northwest Research and Outreach Center at the U of MN, Crookston (Table 1) when Phosphorus was obviously deficient.

Table 1. Effect of P Fertilizer Application on Sugarbeet Yield and Quality,  of MN 1998. (Sims and Smith).

*Soil test level was 6 ppm

Field Conditions That Promote Phosphorus Deficiency:

• Coarse or lighter textured soils
• Low soil organic matter percent
• Low Phosphorus soil test levels (10 ppm or ) <
• Prolonged wet and cold soil conditions

Recommended Phosphorus Management Strategies:

• Soil test and fertilize accordingly in the spring or fall
• Use a Phosphorus starter fertilizer @ not more than 3 gallons per acre
• Build up very low Phosphorus soil test levels

Starter fertilizer Phosphorus gave dramatic yield responses at the Northwest Research and Outreach Center at the U of MN, Crookston in 1999, (Table 2). Use of 3 gallons per acre of 10-34-0 or a very similar starter fertilizer gave sugarbeet yields basically equal to 15, 30, 45, or 60 pounds of P₂0₅ as 0-46-0 broadcast dry fertilizer. Shareholders might consider use of starter versus broadcast Phosphorus to reduce 2001 fertilizer costs especially on rented land with short-term agreements.

Crookston Shareholder Field in 1998

Stand loss versus starter fertilizer use.

Excess use of starter fertilizer may reduce sugarbeet stands. Rates of starter fertilizer greater than 3 gallons per acre did not increase yields in 1999, U of MN, Northwest Research and Outreach Center studies, (Table 2).

Fertilizer Calculator Provides Benefits

Consider use of NPK fertilizer calculator on our website to minimize fertilizer-input costs.

• Compare different fertilizers.
• Compare soil test recommendations.
• Project impact of fertilizer price changes.

Table 2. Effect of Starter and Broadcast Phosphorus Fertilizers on Sugarbeet Yield and Quality, U of MN 1999, (Sims and Smith)

Greatest risk of stand loss from starter fertilizer occurs when applied

• Under dry soil conditions
• At rates > 3 gallons per acre
• On lighter textured soils

For more information on phosphorous management strategies for sugarbeet production see pages 137-148 in the 1998 Sugarbeet Research and Education reports or at www.sbreb.org.