Both fall and spring applications have proven to be effective alternatives to provide nutrients to the crop and there is no agronomic difference in terms of one timing being better at increasing nutrient availability relative to the other.


“Fall is normally the preferred time since typically there is more time and equipment available in the fall than during the planting season in the spring,” Fernandez says. “Also, soil compactionis less of a concern when driving heavy equipment loaded with fertilizer in the fall because soil is typically drier than in the spring, and P and K applications combined with tillage operations are more feasible in the fall.”


One potential drawback for fall applications is the fact that the nitrogen (N) accompanying P in di-ammonium phosphate (DAP, 18-46-0) and mono-ammonium phosphate (MAP, 11-52-0) is more susceptible to loss even if applied late in the fall. However, the amount of N present in these applications is not very high and the benefits of a fall application typically outweigh the potential for any small N losses.


If phosphorus and potassium are at adequate levels, there is no need to make any significant change in the short term when going into a rotation with more corn.


For farmers planning to make a long-term commitment to more corn, remember that overall, corn can remove more P and less K than soybean. Thus, fertilization plans should be adjusted accordingly.


Finally, Fernandez says that before deciding placement method and when and how much to apply, the single most important thing to know is the test level of the soil. To find out, there is no substitute to a regular (every four years) soil sampling program.