The objective of the feed-the-soil approach is to build the soil K level high enough so that crop yield is not limited, whether or not fertilizer K was applied in that season. Thereafter, the intention is to maintain this soil test level by applying crop removal plus 20 pounds of K2O per acre. This is an extremely conservative approach that results in a very low probability of yield loss. However, by design, this approach does not maximize profit in any particular growing season. This was not considered a problem initially 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. 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 profit in a single season (a feed-the-plant or sufficiency approach). With current fertilizer prices, the savings in reduced K application could easily be $50 per acre or more ($25+ if more “normal” prices return in the coming years). This project is designed to develop sufficiency recommendations for K application to corn and soybean on Kdeficient soils where feeding the soil is not the objective. This approach allows the crop to be the driver in production and profit. Preliminary results in our southeastern trial (started 3 years ago) improved soybean yield nearly 10 bu per acre beyond the visual cues of K deficiency with the addition of an additional 90 lb K2O per acre, but still 15-20% less than feed-the-soil K recommendation rates.
This project is about Sustainability, both economic and environmental. Fertilizer and lime are typically about one-third the variable cost of corn and soybean production so economically any time is a good time to use only the correct amount of these inputs. The recent spike in fertilizer prices accentuates the need for appropriate fertilizer recommendations. Tailoring fertilizer applications to maximize profits is not only wise economically, but environmentally as well. Although chloride arising from K fertilizer applications is not yet a target of improving water quality, it may soon be.
Goal 1- Develop fertilizer recommendations that maximize profit for any one year based on the soil test and price of fertilizer and grain. Goal 2- Identify whole plant or leaf K concentrations where crop yield is optimized through tissue testing for in season monitoring. Goal 3- Evaluate the interaction of exchangeable soil K and K budget (K additions – K removal) from fertilizer and crop removal. Research summaries will be produced annually based on the results of the experiments and disseminated in oral and written formats in-person and electronically. Ultimately, we expect to have sufficient data in 3-5 years to produce a robust recommendation that is applicable across a range of weather, soil conditions, and management. The results of the research will be presented annually in oral and written formats as an indicator of the completion of that year’s research. At the completion of the research project a summary of the ISA/ICMC research plus the previous year’s results at the original 3 locations will be drafted that outlines the recommendations for K fertilization that can be discerned at that point in time.