MSU Extension

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.  

There are several reasons for using starter fertilizers when planting corn: 1) enhance early growth; 2) increase corn yields, 3) accelerate corn maturity, 4) apply phosphorus efficiently; and 5) carry micronutrients. Increasing corn yields is the reason most growers apply starter fertilizer. However, the yield benefit of using starter fertilizers depends on several factors. Conditions that increase the probability of starter fertilizers improving corn yields include:

• Cool, wet soils
• Reduced tillage systems having significant surface residues
• Low phosphorus and/or potassium soil test levels
• pH levels below 6.0 or above 7.0
• Low organic matter

Soil temperature significantly affects plant nutrient availability and early root growth. Warmer soil temperatures increase nitrogen and phosphorus mineralization and the growth rate of plant roots. Since it takes a tremendous amount of energy to change the temperature of water, wet soils tend to be colder in the spring.

Table 1. Soil temperature and probability of yield response to starter fertilizer when soil test P levels range from 15 to 30 ppm. (Source: Dr. Darryl Warncke)

The type of tillage operations performed significantly affects root growth and nutrient uptake. Higher amounts of residue at the soil surface will reflect the sun’s energy keeping soils cool and wet in the spring. Therefore, the probability of experiencing a yield response from phosphorus starter fertilizer is greater in no-till and minimum tillage systems than in conventional tillage systems.

In general, there is a low probability of phosphorus in the starter producing a yield response when P soil test levels exceed 30 ppm. However, when planting into high residue conditions in April, including 25 lbs. of actual P2O5 in the starter may be beneficial, even when P soil test levels exceed 30 ppm.

Research conducted by the University of Wisconsin showed a positive economic response to applying phosphorus starter fertilizer in a 2 by 2 band when long maturity hybrids were planted late in the season. This was true even on soils that tested high in phosphorus. The researchers, Larry Bundy and Todd Andraski, developed the term PDRM (planting date as Julian days + the hybrid relative maturity) for estimating the probability of realizing a positive economic response to phosphorus starter fertilizer. For example: the PDRM for a 100-day hybrid planted on May 30 would be 250 (150 Julian days + 100 RM). When the PDRM is greater than 245, the Wisconsin data showed a 60 percent probability of adding 4.5 bushels per acre when starter fertilizer including phosphorus was applied. The economic benefit or cost of this practice depends on the actual corn and starter fertilizer prices.

Table 2. Potential for a yield response to phosphorus starter fertilizer applied to corn for areas in Michigan south of Lansing. (Source: Dr. Darryl Warncke)

Dates will shift from earlier to later going from south to north.

Michigan State University recommends placing the starter fertilizer two inches to the side and two inches below the seed (2 x 2) at planting. This placement method provides a high degree of crop safety and maximizes the opportunity for root interception of the fertilizer. Using this placement, MSU recommends applying at least 25 lbs. of actual nitrogen per acre. The nitrogen rate should be increased to 40 lbs. per acre in no-till or other high residue conditions. In many situations nitrogen in the starter fertilizer provides equal or more benefit than the phosphorus.

Table 3. Potential for a yield response to nitrogen starter fertilizer applied to corn for areas in Michigan south of
Lansing. (Source: Dr. Darryl Warnck)

PPN = preplant nitrogen knifed in or incorporated prior to planting corn.
Dates will shift to later going further north.

Potassium should be included in the starter in no-till/strip-till or when the soil test level is less than 90 ppm. Including potassium in starter fertilizer gives most benefit in high residue and cool, wet soil conditions. Over the past two years potassium application rates have been reduced due to the very high price of potash. As a result soil potassium levels have been drawn down. This also contributes to the importance of providing potassium in the starter fertilizer. Potassium and nitrogen fertilizers can burn the seed so the total amount of N plus K2O should not exceed 100 lbs. per acre for coarse-textured soils and 125 lbs. per acre for fine-textured soils. Again the preceding application rates apply to a 2 x 2 fertilizer placement. If you plan to place the fertilizer directly in contact with the seed, please read the following section entitled “Pop-up Fertilizer Precautions.”

Pop-up fertilizer precautions

Fertilizer placed in direct contact with the seed has the potential to reduce germination. This is especially true when planting into dry soil. As a general rule, never apply more than 5 pounds of N plus K2O on soils having cation exchange capacities (CECs) of 5 meq/100g or less and no more than 8 pounds of N plus K2O soils having CECs of 8 meq/100g or more. Urea, ammonium thiosulfate and boron should not be applied in direct contact with the seed as they are known to adversely affect germination. Research conducted in 2005 by Dr. George Rehm at the University of Minnesota showed that zinc placed in contact with the seed can also reduce emergence in sandy soils.