Source: George Rehm, University of Minnesota Extension

In Minnesota, application of fertilizer in contact with the seed at planting (also called pop-up) has become a very popular practice. From my unofficial and non-scientific surveys at meetings this winter, approximately 75 percent of those in attendance (Minnesota audiences) used this popular management practice. The percentage was not nearly as high in other states and I don't have a good explanation for the difference. Even though placement of fertilizer with the seed is a very popular practice, there are many questions. So, a guide for the use of seed-placed fertilizer is probably appropriate at this time.

CONSIDER THE CROP: Of course, fertilizer can be applied in contact with the seed for a variety of crops. All crops, however, do not have the same tolerance to this mangement practice. Corn and small grains are tolerant of reasonable rates. Suggested rates will be discussed later. However, the soybean crop is not tolerant and there can be serious reductions in emergence if this practice is used. Although the soybean plant can make some adjustment for stand reduction, use of seed-placed fertilizer at any rate for the soybean crop is risky. The same caution also pertains to the edible bean crop.

SOIL TEXTURE: This fixed soil property has a major impact on the use of seed-placed fertilizer. There is a very low level of risk if the soil texture is loam, silt loam, silty clay loam or clay loam. Soils with these textures are buffered against damage. The sandy loam and loamy fine sand textures can be very risky when fertilizer is placed in contact with the seed. For the sandy soil textures just listed, there should be at least 1 inch of soil between seed and fertilizer. Then reasonable rates of fertilizer can be used. This separation is not necessary for the loam, silt loam, silty clay loam and clay loam textures. Farming soils with these textures, numerous growers have reported no problems when about 8 gallons of 10-34-0 are placed with the seed at planting. One producer reported that there was damage: but, the seed zone was excessively dry at the time of planting.

SOIL TEST SHOULD DICTATE RATE: There's not a single rate of fertilizer that fits all situations. The results of a soil test should be used as a guideline. Since nitrogen and phosphorus are the two most important nutrients in a banded fertilizer used at planting, rates should be based on the results of a soil test for phosphorus. Phosphate fertilizer guidelines from the University of Minnesota provide rates for either a band or broadcast application. The suggested banded rate is appropriate for the seed-placed fertilizer. Following this suggestion should be adequate unless soil test P values are very low. For fields with these very low P tests, a combination of banded and broadcast phosphate should be used.

WHAT ABOUT SULFUR?: With the recent interest in sulfur, there have been numerous questions about use of this nutrient in contact with the seed. Field research has shown that the fluid sources of sulfur should not be applied in contact with the seed when soils are sandy (sandy loam, loamy fine sand). There is also some risk associated with seed placed sulfur for other soil textures. Planter attachments that place fertilizer a short distance from the seed should be used if there are plans to use sulfur in a band somewhere close to the seed. For fine textured soils, 1/2 to 3/4 of an inch between seed and fertilizer is adequate. The distance between seed and fertilizer should be at least 1 inch for sandy soils.

NITROGEN IS RESPONSIBLE: Previously, guidelines for use of seed-placed fertilizer suggested that rate should be dictated by the sum of nitrogen and potash applied. However, recent research results have shown that the rate of nitrogen is the most important consideration. To be safe, the rate of nitrogen should be no more than 10 lb. per acre if fertilizer is placed in contact with the seed. This rate can be more than doubled if there is some soil between seed and fertilizer.

FERTILIZER/SEED CONTACT IS NOT NECESSARY: It is not necessary to place fertilizer in direct contact with the seed to get the positive effects on the early growth of the crop. Fertilizer placed in a band close to the seed can produce the same effect. In general, the benefits of the banded placement placement diminish as distance between seed and fertilizer increases beyond 3 inches.

HIGH RESIDUE: High corn yields combined with more conservation tillage and corn following corn as a crop sequence puts special emphasis on management practices to improve early growth. PLacement of fertilizer in a band near the seed is a management practice that is essential for early growth and development in these situations.

For Minnesota planting conditions, there's no doubt that seed placed fertilizer is a good management practice. Unless soils are sandy, there have been no complaints when reasonable rates are used.