Considerations for Using Starter Fertilizer
When choosing a starter fertilizer system that works best for your specific field or operation, there are three main things to consider: the nutrients available/supplied by the material used, application rate, and placement options available. An article on Channel.com looks at each of these considerations, which are summarized below.
Materials. When using a starter fertilizer that contains both N and P, optimum results can be obtained when combining phosphate with ammonium nitrogen. Monoammonium phosphate (MAP; 11-52-0) or ammonium polyphosphate (10-34-0) liquid-based fertilizers are excellent choices. Nitrogen in ammonium form can help to enhance the use of P in the starter as well as P uptake from soil. Generally, starters should contain a high phosphate (P2O5) ratio and the phosphate should be highly water soluble. A fertilizer does not have to be labeled “starter” to be used as such if it meets the needs for your situation and follows basic defined parameters of rate and placement. Depending on soil test results, micronutrients can also be provided in the formulation to meet specific needs. Starter fertilizers can be applied in both solid and liquid forms as generally there is no difference in effectiveness. Liquid fertilizers may be more expensive than dry formulations, but when properly applied can require lower quantities and still be cost effective.
Rates. Generally, only a small amount of fertilizer will be required for a starter response if soil fertility tests are within the optimum range or higher. The appropriate rate of starter to use will depend on: proximity to the seed, salt content or index, and soil texture. Using rates above the recommended limit can cause a salt effect that can impede germination and early plant development. If starter fertilizer is placed 2 inches from the seed, do not apply more than 70 lbs N plus K2O per acre and reduce even further if placed in closer proximity to seed. If starter is placed with the seed (a pop-up fertilizer) the limit should be 10 lbs/acre. Salt index is estimated to be the sum of N + K + 0.5 x S. Problems associated with salt damage may develop if soil moisture is limited within the first few weeks after planting or if fertilizer was placed too close to the seed. Soil texture also plays a role in that fertilizer rates must be lowered when placed within 1-2 inches on sandy soils. For narrower row-widths, the application rate may be increased. It is especially important to follow rate limits in conservation tillage due to the less accurate placement of starter in relation to the seed.
Placement. While N is mobile in the soil, P is bound and does not readily move through the soil. Starter fertilizer allows close placement of P in order for the developing plants to take it in. Placement is crucial because seedling plants must be close enough to access nutrients, but not too close when used at higher rates. The ideal placement for starter fertilizer is in a band 2 inches to the side of and 2 inches below the seed (2×2). This allows the roots easy access to the fertilizer, but limits the potential for fertilizer burn. The 2×2 placement has an advantage over seed-placed starter because it is in a prime location for nodal root development and higher rates can be used without risk to the seed.