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In recent years, there has been considerable interest in an old concept, the application of fertilizer in contact with the seed. This placement, referred to as “pop-up”, was evaluated by several researchers in the late 1950’s and early 1960’s as an effective method of applying fertilizer to stimulate early growth and development of several crops. Use of excessive rates by some aggressive growers, however, caused damage to germinating seeds and alternative placement options were soon developed.

Recent changes in corn production have stimulated a renewed evaluation of the use of the “pop-up” placement option. A brief list of these developments would include:

• subsurface placement of phosphate fertilizer and quality of surface waters
• multi-row planters not compatible with starter attachments
• many soil test values in the medium and high range
• interest in conservation tillage planting systems

Recent research has shown that the use of “pop-up” fertilizers cannot be a universal management practice and all fertilizer materials are not suited for this placement. The “pop-up” term has also been replaced, in many situations, by the phrase “seed placed fertilizer”. The positive aspects of “seed placed fertilizer” as well as some of the concerns will be described in this newsletter.

Fluid Fertilizer and Seed Content

Since there were several reasons for a renewed look at seed placed fertilizers, a trial was established recently to evaluate this concept. To do this, 3 fluid materials (10-34-0, 4-10-10, 7-21-7) were placed in contact with the seed at planting. Each fluid material was applied at rates of 5, 10, and 15 gallons per acre. A control where no fertilizer was applied was also included.

The study was conducted at the Southern Research and Outreach Center, Waseca and the Southwest Research and Outreach Center, Lamberton. Plant populations were measured in early June and grain yields were measured in early October.

Soil tests for P and K were in the high range at both sites. Adequate N (preplant) was used for all treatments at both sites.

Plant Population After Emergence

Stand counts were taken approximately 4 weeks after emergence in order to get some measure of the effect of seed placed fertilizer on stand damage. The population was calculated as the percent of the control (no fertilizer in contact with the seed). The results recorded in 1997 are summarized in Table 1.

Table 1. Plant population after emergence as affected by rate of application of three fluid fertilizers.

At Waseca, there was no substantial reduction plant population indicating that the rates of fluid fertilizer used had no negative effect on germination and early seedling vigor. At Lamberton, the populations as compared to the control were greater than 100%. This was due to a low population count in the control. Nevertheless, the rates of fluids used had no negative effect on emerged population.

Grain Yield

Measured grain yields corrected to 14.5% moisture are summarized in Table 2. When averaged over fertilizer material and rate of application, yield at Waseca was 196.5 bu. per acre. Thus, there was a small increase in production when seed placed fertilizer was used. It is important to note that there was no reduction in yield.

Table 2. Corn yield as affected by rate of application of three fluid fertilizers.

At Lamberton, yield was 138.0 bu./acre when averaged over fluid material and rate of application. This is a smaller increase than was recorded at Waseca. However, there was no reduction in yield when the seed placed fertilizer was used. Thus results from both locations were consistent. There was no harmful effect from seed placed fertilizer at rates that were used in this study.

Some Cautions

Although there have been positive results from the application of fluid fertilizer in contact with the seed, this management practice is not without risk. There are some situations where seed placed fertilizer should not be used. All involve risk.

Dry Conditions At Planting: The potential for damage from seed placed fertilizer increases as the soil dries. This is true for all fertilizers. The soils with a sandy texture dry more rapidly than others. Therefore, there should be special caution when sandy soils are dry.

Avoid Urea: Fertilizer which contains a substantial amount of 46-0-0 should not be placed in contact with seed. This is especially true for calcareous soils where free ammonia is formed before urea-nitrogen is transformed into nitrate-nitrogen. The amount of 46-0-0 N applied with the seed should not exceed 3 to 5 lb. per acre.

Ammonium Thiosulfate Can Be A Problem: This product, 12-0-0-26, is one of two fluid sources of sulfur. This product, if placed in contact with the see, has a negative effect on germination and subsequent emergence. Place fertilizer containing this product so that there is at least 1 inch of soil between seed and fertilizer. This suggestion is especially important for sandy soils.

Boron Can Also Be A Problem: This micronutrient can have a negative effect on germination if placed in contact with the seed. If boron is needed for corn production, it should be broadcast and incorporated before planting.

Summing Up

In thinking about seed placed fertilizer, there are some important points to remember. There are:

• Both fluid and dry materials can be used for this management practice. Fluid materials are usually used because they are easier to meter and handle.
• Seed placed fertilizer is not suggested for soybean production.
• Avoid placing 46-0-0 and 12-0-0-26 in contact with the seed, regardless of crop.
• A rate o 8 gallons per acre of 10-34-0 is adequate for most situations if the soil test for P is not low or very low. Smaller rates (3 to 4 gallons per acre) are suggested if the soil test for P is in the high range.
• The risk of germination damage from seed placed fertilizer increases as soil moisture at planting decreases. This is especially true for sandy soils. Soil moisture content should be a major consideration where this management practice is planned.
• Seed placed fertilizer can substitute for the use of a starter fertilizer with all the advantages of a starter.