Agronomy: Are Starters of Value?

To add or not to add—starters on soybeans. I would like to put this debate to bed once and for all. Over my years as an agronomist, writer and reader, we have seen articles every spring extolling the virtue of applying starters when planting soybeans. But we also receive a word of caution, because they may not increase yield or return a profit.

Now that soybeans are planted and up I noted an article posted online in Ag Professional provided by Kansas State University. You can read it here. It was written by Dorivar Ruiz-Diaz, a Nutrient Management Specialist.

His first tenet: “If fertilizer is recommended by soil test results, then fertilizer should either be applied directly to the soybeans or indirectly by increasing fertilizer rates to another crop in the rotation by the amount needed for the soybeans.” Use a soil test to decide how much of the nutrients you will need, focusing on phosphorus (P), potassium (K), sulfur (S), zinc (Zn) and boron (B). Some agronomists would add: don’t forget manganese and iron.

His second tenet: “The most consistent response to starter fertilizer with soybeans would be on soils very deficient in one of the nutrients (P, K, S, Zn, B) or in very high-yield-potential situations where soils have low or medium fertility levels.” Those numbers are usually less available in the spring when soils are cool and moist, mineralization hasn’t kicked in, and roots are too small and can’t yet access the supply of nutrients in the soil.

The third tenet: “Banding fertilizer to the side and below the seed at planting is an efficient application method for soybeans. This method is especially useful in reduced-till or no-till soybeans because P and K have only limited mobility into the soil from surface broadcast applications.” In no-till soils, placing a band of immobile nutrients near the seedling roots gives them earlier access to these nutrients until roots develop.

Their fourth tenet: “Fertilizer should not be placed in-furrow in direct seed contact with soybeans because the seed is very sensitive to salt injury.” True, if you follow starter rates applied to corn. But if you keep the salt index down to 6 or 7 lbs. by applying 2 gallons of starter and diluting it out further with a couple gallons of water you won’t experience any injury.

My fifth tenet: “Don’t always expect a bump in yield.” Starters applied to corn or soybeans overcome short-term nutrient deficiencies at emergence or during cold springs and work well on some acres, but not necessarily on every acre in a field. But they can help get a crop off to an early and more consistent start in the spring, which it may benefit from later.

All the above tenets are true. However, in my experience the deciding three factors include: 1) is your planter equipped to apply starter, 2) do you mind the inconvenience of tendering starter and 3) is the risk of salt damage to seedlings believed to be too great.

So for those of you who applied starter in 2016, let’s hope you receive a financial benefit from your decision. And, despite the above, come 2017 I believe we’ll be having this same conversation all over again.

Agronomist Dr. Daniel Davidson posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com or ring him at 402-649-5919.