Fertilizer applications often occur before the growing season based off soil test results, crop to be grown, previous crop, and nutrient load needed for a successful crop. A dry growing season can lead to reduced nutrient uptake and overall crop yields, potentially impacting nutrient availability and location within the soil profile when compared to a normal season of rainfall.
Nutrient needs for the next crop should be based on the original yield goal prior to the drought, the nutrients applied prior to the drought, and the estimated crop nutrient removal for the drought stricken crop based on how the drought stricken crop was treated – not harvested for grain or silage, harvested for grain and residue left in field, chopped for silage, harvested for grain and residue baled for feed or bedding.1 Additionally, the nutrient removal can vary depending on when a drought stricken crop is “harvested”. As an example, more phosphorous is removed if a corn crop is removed for grain than harvested for silage at R1 (close to silking) growth stage.1 Conversely, more potassium is removed for silage at R1 growth stage than if a full grain crop was harvested.1
Let’s review the three primary soil nutrients and determine which of these we could be concerned with after a dry year:
Leachable once converted to nitrate. More N may be left in the soil profile following a dry year due to reduced leaching, mineralization, and uptake. However, should considerable rainfall occur prior to the 2022 planting season, additional N may be required for corn because leaching may have occurred.1
Generally immobile in the soil but is prone to loss through erosion. Given optimal nutrient load within a soil, P is still accessible to the plant through root interception, but mass flow and diffusion will be limited in a dry year.2
Most likely the first nutrient you’ll see visual deficiency symptoms of during a dry year. Mobility is less than N in the soil but more than P. Movement within the soil is generally through diffusion. Potassium is crucial for water transport and other metabolic processes within the plant, and generally large quantities are required.3
In summary, we would expect nutrient runoff and leaching to be lessened under droughty conditions. Although a previous crop might have expressed certain deficiency symptoms, nutrient load could have been ideal, and the real limiting factor was water availability needed to uptake those nutrients.
Recommended steps to take prior to additional applications of fertilizer:
Reference your most recent soil test results
Collect yield data from previous crop
Determine nutrient removal estimates based off previous crop and yield
Collect new soil samples for analysis to determine future optimum fertility recommendation.
The University of Missouri article Impact of the Drought on Next Year’s Fertilizer Rates provides formulas and tables to help determine crop nutrient needs following a drought.1 The article was written in 2012 to address future nutrient needs after the drought and heat damage of 2012.
1Lory, J.A. and Scharf, P.C. 2012. Impact of the drought on next year’s fertilizer rates. Integrated Pest Management. University of Missouri. https://ipm.missouri.edu/IPCM/2012/8/Impact-of-the-Drought-on-Next-Years-Fertilizer-Rates/.
2Sawyer, J. E., Creswell, J., and Tidman, M. J. 2000. Phosphorus basics. Integrated Crop Management News. IC-484(20). http://lib.dr.iastate.edu/cropnews/2082
3Hodges, S. C. Soil Fertility Basics. NC Certified Crop Advisory Training. North Carolina State University Soil Science Extension. North Carolina State University. http://www2.mans.edu.eg/projects/heepf/ilppp/cources/12/pdf%20course/38/Nutrient%20Management%20for%20CCA.pdf.
Web sites verified 7/23/21.