Starter fertilizers can be an effective way to supply early nutrients to your corn crop and may be used to supplement broadcast applications, but is there use warranted and what concerns should you have.

Before we get into the actual discussion of starter placement, we will first discuss starter response and the need for starter fertilizer. Early-season response to starter fertilizer in the form of more vigorous growth is common, but the early-season response does not necessarily translate into a yield gain at the end of the season. For starter applications, we would recommend a 2×2 placement simply because we can supply more nitrogen (N), which is normally our most limiting nutrient. Application of starter N will allow us to delay side dress applications (if soybean planting or inclement weather get in the way). Inclusion of phosphorus (P2O5) and potassium (K2O) in a starter package may be warranted if soil test levels for those two nutrients are below the established critical values (Tri-State Fertilizer Recommendations). Soils that have a history of adequate or perhaps even a little excessive P and K fertilization resulting in a high soil test levels are unlikely to benefit (yield-wise) from the inclusion of P and K in the starter. Notice we focused on a yield benefit, often times we can see visual differences due to application of P specifically in cool, wet springs, but it does not necessarily translate into a yield increase. Soils that are low in P and K (below the established critical value) can benefit, especially if broadcast applications were not made the previous fall or in the spring. Starter response is also affected by the tillage regime utilized. No-till systems result in cooler, wetter soils and are more likely to benefit from starter fertilizers than tilled soils. In summary, soils that have adequate P and K levels are unlikely to benefit from starter P and K applications, but soils that are deficient can show a positive response.

With the advent of larger planting equipment affecting our ability to add 2×2 attachments due to weight restrictions or machine folding operations, pop-up, or in-seed furrow, applications of fertilizers may be the only possibility. Application of pop-up materials is much more restricted because we are putting salts and possibly ammonia forming fertilizers near the germinating seed. So how much fertilizer can be placed with the seed? The general rule of thumb used by Ohio State University is 8 lb of N + K2O per acre with the seed. The main factor determining whether or not salt will be an issue is soil moisture at the time of planting. The wetter the soil the more salt that can be applied without any adverse affects on seed germination. Urea-based nitrogen sources and diammonium phosphate (DAP) can be problematic when applied with the seed due to the formation of free ammonia during their breakdown. This too is dependent upon soil moisture, and the wetter the soil the less likely there will be a problem. The recommendation in place by Ohio State University does have a safety factor because we do not have a really good way to determine soil moisture at the time of planting.

SOURCE: OSU

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