Phosphorus and potassium fertilization tips
Annual vs. biennial applications. Is an annual application better than a biennial one? Just as with placement, our research indicates that as long as you apply the needed fertilizer to make sure soil test levels are adequate to supply what the crops will need, no yield benefit hinges on whether the application is done every year or every other year. All that said, we have seen that for biennial applications it is better to apply fertilizer before the corn crop and to have soybean as a residual feeder. Research has shown that planting corn in the second year after fertilization can cause yield reductions, especially in no-till systems. Conversely, soybean yields were not affected in response to the time of fertilization. Even if a biennial application results in saving time and making one less pass over the field, if your experience tells you that your soil does not build up, I would suggest always applying annually.
Fall vs. spring applications. Is it better to apply P and K in fall or spring? Many studies over the years have indicated that both are effective in providing nutrients to the crop, and neither timing is better at increasing nutrient availability. Fall is normally the preferred timing, since typically more time and equipment are available than in the spring planting season. Also, soil compaction is less of a concern in the fall when driving heavy equipment loaded with fertilizer, soils are 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 application is the fact that the nitrogen accompanying P in MAP and DAP 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 (typically no more than 30-35 lb N/acre), and the benefits of a fall application typically outweigh the potential for any small N losses.
Phosphorus and potassium for continuous corn. Do I need to manage P and K differently in a corn-corn than a corn-soybean cropping system? Recently there has been interest in increasing corn acres. In Illinois that most often means putting soybean acres that have been in rotation with corn into a continuous-corn or a corn-corn-soybean rotation. If P and K are at adequate levels, there is no need for significant change in the short term when going into a rotation with more corn. If soil test levels are below recommendations, it is always advisable to establish a fertilization program that will bring them up to sufficiency ranges. In situations of short tenure of the land--where a build-up approach might not be possible--band application at maintenance levels will provide the best management approach.