By Daniel Kaiser
Extension Soil Fertility Specialist
Utilization of liquid fertilizer sources placed directly on the seed at planting has become commonplace in many areas of Minnesota. However, low corn prices as well as challenging planting conditions over the past two growing seasons have caused many to question certain aspects of their overall fertility program. There are a few suggestions that can be used to ensure the best chance for a profitable return on investment
1) Keep Rates Low: Using low rates not only lessens the risk for stand loss but may provide the greatest response while increasing the amount of acreage that can be covered with a given tank of fertilizer. In a recent study funded by the Minnesota Corn Growers and Fluid Fertilizer Foundation, rates of 0-7.5 gallons of 10-34-0 were compared with and without broadcast P applied. Two items of note in this research: 1) the addition of starter increase early plant growth by a similar amount whether broadcast P was or was not applied; and 2) the greatest increase in early growth occurred for the 2.5 gallon rate of 10-34-0, there was an additional small increase in growth when the 5 gallon per acre rate was used over the 2.5, and there was no advantage of 7.5 gallons over 5.0 GPA. From the standpoint of getting the plant off to a faster start, a rate of 2.5 to 5.0 gallons of 10-34-0 (applying 10-20 lbs P2O5 per acre) applied directly on the seed appears to be adequate.
2) Pick a Starter Source and Placement that Works for Your System: Identifying what nutrients will make the most sense for a particular system is critical to ensure the best results. For example, poorly drained soils that are cool and wet can significantly affect uptake of phosphorus. Thus a starter that contains a relatively high amount of P would be best. Nitrogen and sulfur may be more limiting under continuous corn, but high amounts of these nutrients cannot be placed directly on the seed so alternative placements, such as surface banding, must be considered. Application of micronutrients in a band with the planter can be an efficient way to supply them to the plant. However, all our current research data has shown that the only micronutrient that has shown clear response for corn grown in Minnesota is zinc. Studying any research in your given area is important to understand what may be the best course of action and to answer the questions do I need to apply this nutrient in my starter?
3) Know What You are Applying: This is one of the biggest mistakes many make when using liquid starter fertilizers. It is crucial to factor any nutrients applied in the starter within the overall fertility program of a field. A 5 gallon per acre rate of 10-34-0 will apply 20 lbs of P2O5 which should be accounted for by reducing broadcast P rates accordingly. While the cost per pound of a nutrient will likely be higher with a liquid fertilizer source, it is more economical to use starter if you consider it part of your fertility program. Some may consider starter to give additional benefit to their overall fertility program such as growth increases commonly seen early in the growing season. It is important to remember that increased growth does not always translate to increased yield later in the season. Applying nutrients in a band may be more efficient but it does not translate to a higher probability that a yield response to a given nutrient may occur.
4) Evaluate Products on a Cost Per Nutrient Applied: The best way to choose among starter products with similar nutrient blends is to calculate the cost per nutrient applied in the fertilizer. The least expensive source that will meet with management goals is generally the best choice.
5) Do not Fall for the Ortho versus Poly debate: While it is true that polyphosphate is not directly available to plants, the benefits of starters containing 100% ortho-phosphate versus polyphosphate is questionable. Once applied in the soil, polyphosphate is converted to ortho-phosphate quickly enough to supply phosphorus to a corn plant early in the growing season. Sources of phosphorus fertilizer containing polyphosphate also contain a percentage of the total phosphorus in the ortho-phosphate form which should allow enough time for polyphosphate to convert. The ortho- versus polyphosphate debate comes up on a continual basis when comparing products but it should be of little concern when choosing a starter fertilizer source.
Starter fertilizer can be used to enhance an overall fertility program. It is important though to keep with realistic expectations on what starter can and cannot do to enhance the growth and development of a given crop, and for which crops it makes most sense to use a starter. Also, it is crucial to evaluate your program to make an appropriate decision as to what placements and sources work best. There may be multiple options available that make sense and will give a higher likelihood of a positive economic return.
Source : umn.edu