By Gary Schnitkey and Dan Davidson
Today there are two certainties – corn and soybean prices are depressed and corn and soybeans both will yield if fed and managed intensively. Here is the dilemma growers are faced with – do they cut back on inputs to reduce cost and at same time reduce yield potential, or do they continue to invest in yield, albeit smartly based on return on investment? There is no easy answer to this challenge.
After land costs, fertilizer expenses are the single biggest cost accrued when producing a crop. So trimming some dollars from the nitrogen (N), phosphorus (P) and potassium (K) budget may seem like an easy step to save money next season. However, we are pulling off bigger yields every year and 2018 is no exception.
Emerson Nafziger, emeritus with the University of Illinois at Urbana-Champaign (UIUC), reported last fall that corn removes 0.37 lb. P2O5 and 0.24 lb. K2O per bushel and soybeans removed 0.75 lb. P2O5 and 1.17 lb. K2O per bushel. Multiply that through by 250-bushel corn and 75-bushel soybeans and you are removing a lot of pounds annually with the yield you are harvesting.
And we have known for some time now that P and K soil test levels have been declining across the Corn Belt as growers have been taking off higher yields while maintaining similar application rates leading to a drawdown in soil test levels. International Plant Nutrition Institution (IPNI) have been tracking and reporting on trends every 5 years since 2001. In their most recent 2015 summary they reported:
  • “Phosphorus: Over the period 2001 to 2015, North America data indicate fewer samples testing higher in P and more samples testing lower.”
  • “Potassium: Similar to P, the trend from 2001 to 2015 in North American was toward more samples testing lower and fewer samples testing higher.”
With yields being higher and soil test levels declining, can you take a chance on reducing fertilizer rates with the prospect of reducing yield?
One of the key items to examine when deciding whether to apply or not apply are existing soil test levels. If P tests are below minimums listed in the Illinois Agronomy Handbook (somewhere between 40 and 50 pounds) then cutting back on phosphorus applications could impact yield. Similarly, cutting potash applications when below the minimum test levels of 260-300 lb./A minimums will have detrimental impacts on yields. Generally, cutting fertilizer levels such that yields are reduced also will reduce profits. Of course, applying fertilizer above levels that lead to yield increases also will reduce profits. From a profitability standpoint, applying fertilizer to the point where yields do not increase is the key to profitability.
If you are driving for top yields and continually harvesting big crops, cutting back on P and K is probably not a good strategy unless soil test levels are high to very high. However, you can improve nutrient efficiency with both placement and timing.
If you are concerned about the cost of fertilizer there are some steps you can take to improve efficiency.
  • Fertilize corn and soybeans separately and apply in the spring instead of fall. The closer the application time is to crop need, the greater the overall availability and efficiency. Both P and K tend to tie up in the soil and become less available over time.
  • Consider using a product like Avail and Carbond P to increase P solubility availability and efficiency.
  • Band products between the root zone or beside the root zone. Banding increases the concentration and temporarily overcomes the fixation affect found at lower concentrations.
  • Optimize soil health. A healthy soil with good structure, porosity, pH and nutrients will both mineralize nutrients available from organic matter and release organic acids that help keep nutrients available in the root zone.
Soybean agronomist Daniel Davidson, Ph.D., posts blogs on agronomy-related topics. Gary Schnitkey, Ph.D., is a professor at the University of Illinois at Urbana-Champaign and researchers and speaks on farm management topics.

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About the Author: Gary Schnitkey

Gary Schnitkey, Ph.D., is a professor and farm management specialist in the Department of Agricultural and Consumer Economics at the University of Illinois at Urbana-Champaign (UIUC) and regularly contributes content to farmdoc Daily. Schnitkey focuses on farm management and risk management by examining issues impacting the profitability of grain farms including corn-soybean rotations, machinery economics and factors separating profitable from unprofitable farms. Schnitkey grew up on a grain and hog farm in northwest Ohio and received his Bachelor of Science degree from The Ohio State University and a master’s degree and Ph.D. from UIUC.