Mo’ Money Now, or Flexibility Later – Approaches to K Fertilization

The previous approach to potassium fertilization (K) recommended in Indiana was to build the soil K level to (or let it fall to) a soil test level that was high enough so that crop yield was not limited whether or not fertilizer K was applied in that season. The intention was to maintain this soil test level by then applying crop removal plus 20 pounds of K2O per acre. This was an extremely conservative approach that resulted in a very low probability of yield loss. However, by design, this approach did not maximize profit in any particular growing season. This was not considered a problem because most farmers owned the land they farmed or had long-term agreements on the land they rented, so they could reap the benefits of this approach in future years. Maintaining a moderate K soil test level with moderate fertilizer K applications every other year, or every year, gave farmers the flexibility to skip fertilization with a very low chance of yield loss in years when fertilizer was hard to get, or expensive, or commodity prices were low, or if weather prevented the application of fertilizer in late fall, winter, or early spring. Nowadays, farmers typically rent more land than they own and sometimes the leases are short-term or year-to-year. Thus there is more interest, and need, for determining the rate of fertilizer that maximizes yield in this season, and less need to build the soil up to levels where fertilization in any given season can be skipped. My presentation will cover optimum potassium fertilizer rates to maximize corn and soybean yield on soils testing low and very low in potassium and compare profits returned to those based on the build-up/maintenance approach.