Dr. Cristie L. Preston is an Assistant Professor of Sustainable Cropping Systems at the Kansas State University Southeast Research-Extension Center, where her work focuses on soil fertility, crop nutrition, and cropping systems research and extension across the region. Before joining KSU, Dr. Preston served as a technical agronomist in industry, with expertise spanning corn, soybeans, and wheat production systems across the Corn Belt, Central Plains, and Mid-South. She is a Certified Crop Advisor and serves on the Kansas CCA Board. Dr. Preston earned her Ph.D. from Kansas State University in Agronomy and a M.S. in Soil and Environmental Science and B.S. in Animal Science from Virginia Tech. Dr. Preston has spent the last decade helping farmers bridge the yield gap by helping them make better Nutrient Management decisions.
Q: What are things I should watch for applying potassium with a planter?
A: If you are considering the application of potassium with your planter make sure it is accounted for when determining your “safe” rate of fertilization. For 2×2 applications, keep your total salt (nitrogen plus potassium) rate around 80 to 100 pounds per acre. For in-furrow applications, keep your total salt rate around 5 for coarse textured soil and 8 for heavy textured soils.
Q: How much fertilizer can I apply without doing any damage to the seed or soil structure? Is there any sensitivity of seed with fertilizer that I should I be aware of if I apply fertilizer when planting?
A: When considering any type of starter fertilizer application (whether it is 2×2 or in-furrow with the seed) we have two primary concerns – salt and ammonia. Salt is relatively easy to calculate. It is the sum of nitrogen and potassium that you plan to make per acre. The further away from the seed furrow the higher the salt application rate can be (see answer above for more info). Ammonia is toxic to germinating seeds at relatively low levels, so minimizing the exposure risk is key. Ideally, we would want to avoid urea-based in-furrow products. If urea-based products are going to be applied with the seed, the more acid the solution the better (decreases the chance of producing free ammonia). Also, avoid basic (alkaline) fertilizer materials being applied with the seed. The best example here is MAP (monoammonium phosphate) versus DAP (diammonium phosphate). Monoammonium phosphate creates a slightly acidic pH in solution when it dissolves, and DAP creates a slightly basic pH. DAP has a much higher risk of producing free ammonia than MAP, and is therefore a greater risk to the germinating seed.
Q: How much should I be concerned about salt levels with starter fertilizers causing damage to my crop?
A: Do consider the salt level of the starter material being evaluated. We have a way of determining the salt index of any fertilizer solution. The lower the salt index, the lower the risk of salt injury for the germinating seed. Obviously, rate is still a major consideration, but at equivalent rates, a lower salt index product is safer. Salt index is based upon the source material used to create the fertilizer liquid.
