Relay-cropping-adapted soybean varieties for pennycress intercropping systems

Overview

This offering presents advanced soybean breeding lines developed at the University of Minnesota specifically adapted for relay cropping into pennycress, a winter oilseed cover crop. Midwest growers currently lose potential profit when farmland sits fallow over winter. Pairing pennycress with maize and soybean rotations enables sustainable intensification, producing three crops in two years while maintaining a continuous living cover that reduces nutrient leaching and erosion. Pennycress seed is processed into bio-aviation fuel, with the protein byproduct utilized in animal feed, creating a new revenue stream for rural communities.

The core challenge addressed is that soybeans relay-planted into pennycress compete for resources over approximately six weeks and face multiple biotic stressors. No soybean varieties on the market are currently adapted for this system, and yield risk remains the largest barrier to producer adoption. This work identifies and develops genetic lines that minimize yield loss while maintaining the agronomic and economic benefits of the relay system.

Technical specifications

Target traits for relay-cropping adaptation:

• Early season vigor to establish quickly after planting into a standing pennycress canopy
• Fast canopy closure to capture available light once pennycress is harvested
• Shading tolerance to withstand the two-week period when pennycress canopy closes over emerging soybeans
• Allelopathy tolerance to manage chemical interactions from the living pennycress stand

Validation approach:

• Field testing of 40 soybean genotypes across five Minnesota environments, totaling 1,200 plots across over four acres
• Significant genotype-by-management interactions observed, confirming heritable variation for relay-cropping adaptation
• Best-performing genotypes under monoculture were not the best performers under pennycress relay cropping
• Some promising lines showed minimal yield reductions under relay cropping
• Certain genotypes exhibited increased pod counts due to favorable changes in plant morphology
• Seedling vigor, measured through the University of Minnesota breeding program, is proposed as a proxy trait for screening additional varieties

Cropping system workflow:

• Pennycress is planted in late fall after maize harvest, germinates, forms a rosette, and goes quiescent over winter
• Soybeans are planted into pennycress stands before late-spring bolting
• Pennycress canopy closes over emerging soybeans for approximately two weeks
• Pennycress senesces in late May and is harvested in early June, uncovering soybeans for normal growth resumption

Technology readiness level

This research is at an advanced validation stage. Multi-environment field trials have already been completed across five Minnesota locations with 40 genotypes, identifying promising lines with minimal yield reduction under relay cropping. The next phase involves scaling up to on-farm trials utilizing the most promising genotypes identified in prior work, with the potential to conduct this research in the next growing season. The proposed work leverages existing seedling vigor screening infrastructure within the University of Minnesota breeding program to expand variety evaluation. The relay cropping system itself has a 15-year history of pennycress breeding, with elite varieties regularly yielding 1,500 pounds per acre, providing a proven agronomic framework for deploying these adapted soybean lines.