Even in March, wet soil conditions can make farmers nervous. When soils warm and dry as the calendar advances into April, crop producers will finalize corn planting procedures planned for 2010. We usually have several rainy periods that challenge us for the days fit for putting the seed in the ground. Maximizing the hours the planter can operate is a high priority so the question is often posed, “How important is starter fertilizer and what should be in it?”

Dr. Robert Mullen, Ohio State University Extension soil fertility expert advises that soils that have a history of receiving adequate or 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. However, we can see visual differences due to application of P specifically in cool, wet springs, but it rarely translates into a yield increase. Western Ohio fields that regularly receive manure often have high P and K levels.

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. The nutrient that typically provides the biggest starter boost is nitrogen (N). If nitrogen uptake by the corn crop is relatively low in the spring and increases as the crop matures (really taking off around V7-8), why the benefit? Response to starter nitrogen depends upon when sidedress N is applied and upon soil moisture after the application of that sidedress N.

Remember nitrogen is mobile in the soil as nitrate, but it requires soil moisture to promote its movement. Positive yield responses to starter nitrogen are typically seen in cool, wet springs when sidedress N is delayed and mineralization (N release) of organic matter is slowed. Yield responses are also more likely when sidedress applications are made in dry soils.

Many testimonials have been made about the value of sulfur in a starter. Without a doubt, the amount of sulfur deposited in rainfall has decreased over the last few decades, indicating that sulfur responses may become more common place.

At present, Dr. Mullen’s Ohio field trials evaluating sulfur response show that the probability of sulfur response by corn and soybeans is still quite low, with a few exceptions. Soils most likely to benefit from starter sulfur are sandy and low in organic matter (< 2.0 percent).

Cool, wet soils that decrease mineralization of organic matter may be more responsive to S fertilization, but again Mullen’s data does not suggest that starter S is needed everywhere. He suggests that farmers should focus on low organic matter, coarse textured soils when considering S fertilization. Regularly manured fields are also not likely to need S in a starter.

Should you invest in a micro package as part of your starter?  Micronutrient fertilization in a starter band can be an efficient way of providing the crop with those necessary nutrients. Consider the following simple rule of thumb: if a micronutrient deficiency has never been identified or confirmed for a field, then a micronutrient package is less likely to be necessary. Once again, remember that fields receiving routine applications of manure are also enjoying what used to be called the “unidentified growth factor” … micronutrients.

Readers with questions or comments for Roger Bender may write to him in care of this publication.