Using a Starter Fertilizer
The term starter fertilizer refers to a practice, not a material. Starter fertilizer is placed strategically near seed so that it is readily available. This practice improves early seedling growth during cool growing conditions and can help produce earlier-maturing and higher-yielding crops.
Cool, wet soils (even high-fertility soils) reduce root growth and mobility of nutrients, especially phosphorus, thus limiting the availability of soil nutrients to the seedling plant with its very small root system.
To achieve the starter effect, place the planter fertilizer so as to give the roots ready access to the fertilizer while protecting the seed from fertilizer damage. The standard placement, 2 inches beside and 2 inches below the seed, meets the above criteria for a wide range of materials and rates. For this placement, the material should contain less than 30 pounds of nitrogen as urea, and the rate should supply no more than 60 to 70 pounds of nitrogen plus potash per acre. Generally, high rates of starter fertilizer are not necessary. There is more potential for problems from too much starter fertilizer than from too little. By reducing the rate of starter fertilizer and using the proper materials, you can reduce the distance between the fertilizer and seed from the 2-by-2-inch placement.
When you have reduced the distance to the point where you are placing the fertilizer directly along with the seed (pop-up), make sure the application rate supplies no more than 10 pounds of total nitrogen plus potash. Improper placement or excessive rates of starter fertilizer injure seedlings and reduce stands. Limited soil moisture during germination and seedling emergence increases the chance of seedling injury.
Placing starter fertilizer on the soil surface either over or beside the row will reduce its effectiveness in stimulating early-season growth.
Apply 100 to 300 pounds per acre. The data in Table 1.4-6 show the corn yield response from starter fertilizer in a recent three-year study on soils testing high in P. Early season growth was improved with both N and P fertilizers, but grain yields were similar.
The ideal starter fertilizer depends on existing soil nutrient levels. On soils with optimum or low P and K levels, a good complete starter fertilizer should contain a high percentage of P2O5; for example, N-P2O5-K2O ratios of 1-2-1, 1-3-1, 1-4-2, or 1-5-0 are common. Where P levels are high, increasing the N and decreasing the P in the starter should be considered. Often some starter response in these soils can be achieved with N alone and thus reduce the N recommendation. If N is increased in the starter or if you use an N only starter, ammonium sulfate is the preferred material. Be careful using urea in a starter because there is some risk of seedling injury, and keep 2-by-2 rates to less than 30 pounds of nitrogen as urea or move the placement more off the row to 4 inches. Monoammonium phosphate (MAP) is preferred over diammonium phosphate (DAP) as a starter fertilizer ingredient. Both dry and liquid fertilizer materials perform well.
Crop requirements for phosphate can be met by band applying all the phosphate in the starter fertilizer. Do not allow the nitrogen plus potash in this starter application to exceed 60 to 70 total pounds per acre.
When planting early or on soils with marginal potash levels, a starter fertilizer containing some potash is recommended. Some research has shown benefits to adding K to the starter in no-till soils, even at optimum K levels.
Micronutrients and secondary (Ca, Mg, and S) nutrients usually are not necessary in starter fertilizers unless you have strong reason to suspect nutrient deficiencies based on plant symptoms or analysis.