Research-based recommendations on nutrient management are critically needed to support soybean production in Northwest Minnesota. This project will evaluate optimal strategies for fertilizing soybeans in a corn-soybean rotation by fulfilling two primary objectives. The first objective is to determine whether applying two years of phosphorus (P) during the corn year of a corn-soybean rotation provides adequate soil fertility during the soybean year. The second objective is to evaluate whether different P sources perform better than others at supplying P to the soybean crop when comparing two-year applications to single-year applications. This project would take place on previously established, replicated research plots at the UMN Northwest Research & Outreach Center. The previously established plots evaluated P source and rate on corn in 2022 and 2023. In 2023, we followed these treatments through to soybeans for one year of preliminary data collection. The corn project ended after the 2023 growing season. This request seeks funding to complete a second year of data collection in 2024 that will again follow treatments through the soybean year. Findings from this project will improve UMN’s nutrient management recommendations for corn-soybean rotations in Northwest Minnesota. This year’s funding request only includes one trial location, but Dr. Pease is interested in expanding this trial to additional locations throughout Minnesota in 2025. Another goal of this request is to seek funding to provide additional soybean fertility education to growers that is tailored to the soil types and crop rotations found in Northwest Minnesota.

The overall goals of this project are to evaluate optimal strategies for fertilizing soybeans in a corn-soybean rotation and to provide improved education on soybean fertility to NW MN growers. We will meet these goals by achieving the following objectives:
1. Determine whether applying two years of phosphorus during the corn year of a corn-soybean rotation provides adequate soil fertility during the soybean year.
2. Evaluate whether different P sources perform better than others at supplying P to the soybean crop when comparing two-year applications to single-year applications.
3. Develop educational and outreach material on viable strategies for fertilizing soybeans that are tailored to the soil types and crop rotations found in Northwest Minnesota.

These results will help farmers manage risk(s) associated with soil fertility management. Outreach will focus on the agronomic best practices observed in the trials and fertility implications of the different P sources and application strategies. Project findings will be shared with farmers at winter Extension meetings, at summer field days, and through fact sheets, news articles, social media, and on radio, and with the scientific community through society meetings and peer-reviewed publications. Specific examples are outlined below.
• Improved understanding of how different phosphorus fertility strategies perform in high pH soils such as those found in Northwest Minnesota
• Improved fertility recommendations for corn in NW MN
• Presentation of project findings at local and regional extension events such as the UMN NWROC Crop & Soils Field Day
• Communication of project results via extension events and online media
• Development of revised/updated fertility recommendations tailored to growers in NW Minnesota

Updated September 3, 2024:
Field plots were chisel plowed following corn harvest in fall 2023. Immediately prior to planting P fertilizer was applied by treatment and the field was cultivated with a harrow. Soybeans were planted on 5/14/24. Stand counts were taken on 6/14/24 and tissue samples were collected on 7/8/24.

Early season stand counts showed that plots with single-year applications of MESZ had significantly lower stand counts than plots with a two-year application of MAP+Struvite (p=0.0187), single-year applications of MAP+Struvite (p=0.0279), and plots with a single year of MAP applied prior to corn (p=0.0554). All other stand count comparisons were not significant (p>0.10).

This project was designed to provide information of value to Minnesota soybean producers on the efficacy of different fertility management strategies. Fertilizer application represents a major input of both time and resources for growers when measured across all acres. This project will help to reduce the personal risk that growers would encounter when deciding how best to manage soil fertility in rotation with soybeans. Because soybeans do not require nitrogen fertilizer, growers may wonder whether they can save time, fuel, and tillage by skipping a year of applying fertilizer to soybeans. This project was designed to provide an answer to this question.