Drought is a simple and unfortunate fact of life that farmers must endure from time to time. Those who went before us endured these challenges, and so will today’s farmers. Nevertheless, given ongoing extreme weather conditions, it’s sensible to review a few of the basic considerations farmers must weigh when planning fertilizer applications for their suffering fields.
A good starting question to ask about your drought-affected crops: How much nutrient removal was there from last harvest? If you previously baled the corn, sorghum or other crop biomass, then nutrient removal will be different than if you harvested it normally and left stalks remaining. If nothing was harvested, then of course, removal was zero. In cases of zero removal, the majority of the fertilizer you last applied should still be present in the system moving forward — either in the soil or in the crop residue. So some carryover or credit for the next crop will be likely.
A good idea: Soil tests will determine the nutrient status of fields where crops were drought impaired. It’s also smart to consider the amount of nutrients present in the remaining residue and how quickly those nutrients will become available to crops. Nutrients carried over in drought-affected areas may include:
- Mobile nutrients such as nitrate, sulfate and chloride in the soil profile
- Immobile nutrients such as phosphorus (P), potassium (K) and Zinc (Zn) in the surface soil
- Nutrients in crop residues
Among the first tools farmers should think about when planning future fertility programs is a deep profile (at least 2 feet down) soil test for the mobile nutrients, especially nitrogen (N). It’s likely that some N will remain in the profile for use by the subsequent crop, and a soil test is the best way to tell. The immobile nutrients (for example, P, K and Zn) can be measured using a surface sample (only 6 to 8 inches down). With P, the availability and carryover is not always clear-cut, since P reacts in some soils to become less available over time; but, again, soil testing is the best tool we have to make the determination. Potassium usually has a high carryover potential, since in all but a few specific cases it remains available over time.
The bottom line for drought-affected areas is the high probability that carryover of nutrients can be factored into your current application, and given the stress that drought exerts on crops, experts advise making an effort to account for residual nutrition, too. Soil testing remains one of the best tools available for the job.
For more details on the subject, refer to the sources below, as well as ongoing issues of Insights from the International Plant Nutrition Institute (http://www.ipni.net/insights):
Fertilization After Drought, Winter 2011-2012, No. 7, http://www.ipni.net/pnt)
Nutrient Management After Drought, Nov. 2011, http://www.ipni.net/insights)