Ontario legacy database for phosphorus and potassium research in corn and soybean

Objectives:

• To consolidate an open access “legacy” database of experiments that studied the yield responses of corn, soybean and wheat to phosphorus (P) and potassium (K) fertilization.
• To establish an on-farm network of trials for addressing gaps identified in the previous objective on P and K research for corn, soybean, and wheat.
• To revisit correlation and calibration models for P and K by incorporating covariates related to yield potential, soil characteristics, and weather.
• To evaluate P and K rate effects on crop removal coefficients for corn and soybean in Ontario.
• To create an open-access web tool that enhances the accessibility of data and results.

Expected Impacts:

• Revisiting the soil test correlation will deepen the understanding of driving factors behind the response to P and K fertilization. For example, the absence of response to P when soil test P levels are below reported critical soil test values (CSTV) could be a consequence of not considering covariates (e.g., soil texture) in existing correlation models or to estimation bias introduced by the statistical method used to determine the CSTV.
• Updating and reviewing the calibration models by including new covariates such as yield potential, soil characteristics, and weather variables will assist to enhance the P and K fertilizer use efficiency and profitability of the fertilization practice. Overall, a third of Ontario agricultural soils are likely deficient in P or K, representing about 0.8 million acres of corn and 1.1 million acres of soybean. Updated data are needed to make more informed decisions on the best P and K fertilization strategy to use. For example, based on estimates from 99 historical corn trials in ON (Bruulsema, pers. Comm.), with soil test P (Olsen) levels below 12 ppm (about 17% of ON soils), a yield gain between 2-5% may be expected in response to 10 lbs/ac of P₂O₅. For 180 bu/ac corn, this may represent a benefit between 4 to 9 bu/ac (up to $40/ac). Similarly, if updated recommendations help to identify a potential surplus of 10 lbs/ac P₂O₅, it may assist farmers to reduce fertilizer costs by about $9/ac.
• Refining estimations of optimal P and K rates and the effects of nutrient removal levels on low to medium soil test levels will help to reduce the risks of both soil fertility degradation and negative environmental impacts due to misleading rate recommendations.
• Making the database and results public and offering an interactive web tool will allow stakeholders to explore the data with flexibility and will ultimately improve the perception and confidence in the Ontario Ministry of Agriculture, Food and Agribusiness (OMAFA) nutrient recommendations. This project is expected to reflect a high level of commitment to data management transparency and to serve as an example of future efforts toward open data practices.

Project Overview:

Phosphorus (P) and potassium (K) fertilizer recommendations from OMAFA for corn, soybean, and wheat are now outdated. Key factors reducing the confidence in these recommendations are: i) the guidelines are based on data from several decades ago, and ii) variables such as crop yield level and soil properties are not yet integrated into the recommendations. For instance, considering 2018-22 average yields and reference crop removal rates, current guidelines suggest P rates less than crop removal if soil test P levels are >7 ppm in corn and soybean, and 5 ppm in wheat; and K rates less than removal if soil test K levels are >80 ppm in corn, 60 ppm in soybean, and 30 ppm in wheat. Unsurprisingly, soil test P and K values declined in Ontario during the past 2 decades until 2020, when the statistics marked 34% and 38% of soil samples to be below critical soil test P and soil test K levels, respectively.

Performing regular reviews is essential to identify gaps and strategically design plans for updating guidelines. This project will consolidate and publish an open access “legacy” database of historical and new experiments studying P and K yield response in corn, soybean, and wheat crops in Ontario. The initial database with historical experiments will serve to identify gaps of underrepresented scenarios (e.g., soil types, geographic locations) to strategically establish a network of on-farm trials that will assist in closing a gap of more than a decade of scarce experimentation on P and K in corn, soybean, and wheat. Finally, the knowledge-transfer plan will focus on the development of an open-access and interactive web tool that facilitates the accessibility of the data and results of the project to stakeholders, ultimately fostering the confidence and adoption of nutrient management recommendations.

External Funding Partners:

This project was funded in part by the Ontario Agri-Food Innovation Alliance, a collaboration between the Government of Ontario and the University of Guelph.