The Tri-State Fertilizer Recommendations provide the foundation for agronomic nutrient management recommendations from the land-grant universities in Ohio, Michigan and Indiana. The original publication, which came out in 1995, has been comprehensively updated with the release of the 2020 Tri-State Fertilizer Recommendations for Corn, Soybean, Wheat and Alfalfa.
The publication relies on Ohio-generated data from 198 farmer-coordinated, on-farm trials in 39 Ohio counties and long-term plots at OARDC Ohio Agricultural Research and Development Center Agronomic Research Stations conducted from 2006-18. This data validates the recommendations against modern hybrids and varieties and agronomic management practices under current weather conditions. Key recommendations from the guide are included here.
A well-though-out, standardized method to collect soil samples to submit to a lab for testing is a critical component to effective nutrient management decisions. Samples collected every three to four years at the same time of year, with a consistent sampling depth, are key. For each field, determine representative sample areas no greater than 25 acres in size, though grid or zone sampling is preferred. Collect 10 to 15 cores per sample area, and then bulk and bag soil. Samples collected should be sent to a soil testing lab using test procedures approved for the three states as soon as is practical.
Focus on pH
The first item on the Soil Test Results Report (STRR) to focus on is pH. Soil pH maintained in the range of 6.0 to 6.8 remains the target range for common grain and forage crops grown. A variety of liming products are available to adjust any pH out of that range using the buffer pH value on the STRR as a guide to develop the lime recommendation.
The framework for phosphorus and potassium recommendations remains a build-maintenance approach, with important revisions. The buildup range is now recommended but not required. The drawdown range has been removed, resulting in recommended zero fertilizer rates now occurring at the end of the maintenance range. Both changes recognize current agriculture practices and economic considerations, such as the amount of rented land, plus adoption of increased intensity and frequency of soil sampling.
Critical levels for all crops are largely consistent with the original recommendations, except for revising the values to reflect Mehlich-3 as the soil extractant.
Crop removal rates were updated with analysis results from grain collected during recent field experiments that measured P and K nutrient concentrations. Nutrient removal rates per bushel of grain have decreased, especially with potassium. This represents an opportunity to save on fertilizer costs.
Optimizing nitrogen management is challenging and requires careful consideration of 4R nutrient management principles — the right rate, right source, right placement and right timing — all interact to affect exposure of nitrogen to environmental losses, which greatly influence the N available for plant uptake.
Rate recommendations for nitrogen in corn will continue to be based on the economic return model, maximum return to nitrogen (MRTN). This model measures the yield response to each added unit of nitrogen to determine where N cost exceeds returns, thus maximizing farmer profitability. The model with Ohio data for soybean-corn and corn-corn rotations is available at the website cnrc.agron.iastate.edu.
The guide also provides general guidelines on managing calcium, magnesium, sulfur and other micronutrients. Generally, soils in Ohio supply adequate amounts of these nutrients to meet crop needs for commonly grown grain and forages. The exceptions are for certain soil conditions such sandy or low-organic-matter soils, where boron or sulfur can be a concern; or high-organic-matter soils with acidic or alkaline pH conditions outside those ranges normally recommended for crops where copper, manganese or zinc can be a concern.
Find out about the availability of printed or electronic copies of the 2020 Tri-State Fertilizer Recommendations for Corn, Soybean, Wheat and Alfalfa through your local county Ohio State University Extension Office or at extensionpubs.osu.edu.
LaBarge is a certified crop adviser, a certified professional agronomist and a field specialist in the agronomic systems department of OSU Extension. He can be reached at email@example.com.