This project will develop feed-the-plant or sufficiency potassium (K) fertilizer recommendations for corn and soybean on K deficient soils by conducting field experiments with rates of K fertilization. The field areas on which this research will be conducted have not received K applications for many years to specifically prepare them for this type of research. With limited funding, we initiated this research 2 years ago in east-central and northeastern Indiana and 3 years ago in southeastern Indiana. We propose to continue research at these 3 locations and initiate new research on 2 additional field sites in west-central and northwestern Indiana. The outcome of the project will be K recommendations that maximize profit in the season of application by applying the most cost-effective rate of K fertilizer. Current feed-the-soil recommendations do not maximize profit, but produce a sufficiently high soil K level that affords the farmers the flexibility to forgo K fertilization for any number of circumstances with little chance of crop yield reduction. Cash rent and high fertilizer prices are two of the reasons farmers are interested in the most economical fertilizer rate for one year at a time.

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.

Results will be disseminated to farmers, their advisors, and governmental and non-governmental organizations involved in agriculture in presentations by Purdue personnel in-person and electronically. Camberato and Casteel present orally to thousands of farmers and their advisors annually at field days, conferences, trainings, meetings, and via podcasts. Printed materials are posted to the internet through Purdue-supported websites such as the Chat and Chew Café, The Kernel, Pest&Crop Newsletter, and SoilFertility.Info. We expect this research and resultant recommendations will also be publicized by the farm press, such as Indiana Prairie Farmer. Support of this research by ISA and ICMC will be acknowledged when this research is presented.

Purdue Agriculture Center personnel have been dedicated to maintaining these plot areas without K fertilization for many years, specifically for this type of research and they will continue to maintain the plot areas as we then examine the residual effects of previous years of K fertilization. Utilizing this research resource is the primary mechanism for developing evidence-based K fertilizer recommendations. This research will define the K fertilization rate needed to economically optimize K fertilization for corn and soybean. If regulation of chloride (about ½ the weight of the primary K fertilizer used in Indiana) in streams and rivers becomes a reality, this research will help defined the economic impact of regulated potash applications or the necessity of switching to an alternative, likely costlier, source of K.