Summary Content
The goals of this project were to assess productivity of soybeans in sole crop, cover crop and double cropping systems in real farms and under real management and real weather conditions, and to identify and quantify local bottlenecks for cover crop and double crop implementation at the field scale.
On-farm experiments
In 2024, we installed two on-farm experiments into contrasting environments on a farm near Le Sueur, Minnesota. At each experiment, we planted soybeans following a rye cover crop in four planting dates. Planting dates were in accordance with soybean sole crop, soybean after a cover crop, soybean after a winter barley crop and soybean after a winter wheat crop.
Findings
The experiments explored environments with different productivity associated with soils. The conventional system attained 82 bpa in the experiment in the lower position of the landscape, and 75 bpa in the higher drought prone landscape position (Figure 1). Cover crops and the simulated double cropping after winter barley or winter wheat imposed severe penalties on soybean yield. The yield penalty increased as the planting date of soybean in the system was delayed.
Our on-farm experiments revealed significant trade-offs between alternative soybean systems and the conventional sole-crop approach in a relatively favorable 2024 season. While the conventional system consistently produced high yields (75–82 bpa), both the cover crop and double-cropping systems imposed yield penalties, primarily due to delayed planting and shortened crop cycles rather than water limitations. Double cropping with winter barley further reduced soybean yields by 11–13 bpa but offered a potential system-level economic advantage due to the added barley yield and associated ecosystem benefits. In contrast, the winter wheat–soybean system showed the largest yield penalties, especially in drought-prone landscapes, with delayed maturity, which also can increase frost risk and instability. A key but not surprising finding seems to be the significant and consistent negative impact of planting delays on soybean yields, with losses exceeding 1 bpa per day. This highlights the critical role of the winter cereal cycle, particularly the timing of its harvest. A few days of variation in planting dates can determine whether double-cropping will result in a benefit or a penalty for a grower. Future studies should precisely assess and quantify how small shifts in soybean planting dates, driven by variability in winter cereal cycles, management practices, or harvesting cereals for silage, impact soybean yield and yield stability and profits of the entire system. Overall, our findings suggest that while diversified systems can offer soil and weed management benefits, their economic viability could be highly sensitive to planting dates, variety selection, and site-specific water dynamics.
Figure 1.
Table 1.
