We will leverage the Science for Success team, a coalition of nationwide Soybean Specialists, to quantify soybean N credits across the US. To date, there has never been a nationally coordinated effort to quantify N credits from soybean. If N application rate to subsequent crops can be reduced by accurately quantifying N credits from soybean residue, this provides evidence of the economic and environmental value of soybean as a sustainable rotational crop.

The goal of this project is to quantify soybean N credits across the US. The objectives of this proposed work are to:
1. Quantify total C and N of soybean residue after harvest, across a wide range of weather, soil, management practices, and yield levels.
2. Determine total soybean N credits to the following nonlegume crop.
4. Identify weather, soil, and crop management variables that could be used to predict soybean N credits across the US soybean regions.
5. Disseminate results to soybean farmers and other stakeholders through the United Soybean Board’s Science for Success initiative.

1. Collect soybean residue from field experiment after harvest from 14 states across the US & analyze for total C and N.
2. From field experiments, create N response curve of nonlegume crop response to cropping history to quantify soybean N credits.
3. Produce at least 1 Fact Sheet, 1 webinar, and 5 videos by project completion.
4. Train at least one PhD student and 10 undergraduate students by project completion.

Update:
Mar. 19, 2024: Waiting for funding to arrive. Site selections completed.

Updated May 31, 2024:
Project summary
The project's primary objective is to quantify nitrogen credits from soybean to subsequent crops, so that producers can apply appropriate amount of N fertilizer to optimize crop yields following soybean. The project has been successfully initiated across 14 states in United States. This report outlines the establishment process, the collection of time zero soil samples from the 14 sites. Next steps not only involve laboratory analysis, but also management of the field trials.

Project establishment across 14 states
We are pleased to report that the project has been successfully initiated across 14 states. These states were selected based on their significant soybean production and diverse environmental conditions, which will provide a comprehensive dataset for our study.

Collection of time zero soil samples
A critical component of our research involves collecting soil samples at the "time zero" (0 to 6 inches), which represents the baseline soil conditions before the planting of the subsequent crop. Our research teams have collected soil samples from each trial site in the 14 states. The sampling process was standardized to ensure consistency across all locations.

Sampling protocol: Soil samples were taken from multiple points within each field to account for variability. The samples were collected at a depth of 0-6 inches and the collected soil samples were bulked to obtain a homogeneous samples.
Sample handling: Collected samples were immediately stored in cool, dry conditions to preserve their integrity. Each sample was labeled with detailed information, including the field location, date of collection, and soil depth.

Laboratory analysis
We are now in the process of sending the collected soil samples to laboratories for detailed soil analysis. The laboratory tests will focus on the following parameters:
• Soil inorganic nitrogen: Both organic and inorganic nitrogen forms will be measured to determine the total nitrogen available in the soil.
• Carbon content: Samples will provide native soil C:N ratios, which will inform the potential for soil mineralization or immobilization of crop residues. This will provide a baseline knowledge on the overall soil health. We will also analyze for texture, pH, CEC, and mineral nutrients.

Project deliverables:
We are currently working on a review manuscript that we plan to send out for review before the end of the year. Additionally, by the end of the year, we will present our preliminary results at the American Society of Agronomy Conference (ASA).

View uploaded report

This project has the potential to save soybean farmers money by applying soybean N credits to subsequent crops. For example, if the N rate to a subsequent nonlegume could be reduced by 20 lb N/ac while maintaining yield, at current prices, a farmer would save $13.60/ac. Current N credit recommendations need to be revised, especially in consideration of new soybean varieties, management practices, record yields, and weather conditions. Our proposed work will provide a robust framework to quantify N contributions from soybean residue using modern cultivars and management practices representative of soybean farmers across the US.