Boosting Soybean Yield: the Role of Spring-Planted Winter Barley, Winter Rye, and Winter Camelina in Salinity Mitigation

Soil salinity is a significant challenge in North Dakota, affecting over 1.9 million acres and reducing crop yields. Often marked by a white crust, saline soils have high soluble salts like sulfates, carbonates, and chlorides. Soils with electrical conductivity (EC) over 4 mmhos/cm are considered saline, but soybean yields can drop by 20-25% with EC levels above 1.1 mmhos/cm, reaching 50% loss at 2 mmhos/cm.

Mitigating salinity in ND relies on water management, and cover crops can reduce evaporation and improve drainage. Winter cover crops need vernalization for anthesis, and because of that, spring-planted winter rye, winter camelina, winter barley, etc., remain in the vegetative stage. They act as green mulch between the soybean rows, decreasing surface evaporation and adding root channels that increase soil water drainage. Adding a cover crop in the system also improves microbial communities' biodiversity.

This research was conducted in Carrington, ND 2024, under dryland conditions in a saline area with an electrical conductivity (EC 1:1) gradient ranging from 0.6 to 3 mmhos/cm. The trial followed a randomized complete block design with treatments including soybean (check), soybean with winter rye, winter barley, winter camelina, and a cover crop mix. Each cover crop was planted at 66% and 33% of the recommended seeding rate. The cover crop was either terminated at the R2 stage of soybeans or left in the field without termination. Cover crops were planted on May 5, and soybeans were planted by June 21, 2024.

Results and Conclusions

Winter barley, winter rye, and the cover crop mix achieved the highest green cover values, exceeding 30%, and provided effective mulch during the early stages of soybean growth (Figure 1a). Soybean plants reached the R2 stage by July 25, when cover crop biomass was sampled. Winter camelina and the cover crop mix, seeded at 66% of the recommended rate, produced significantly higher biomass, averaging over 2,000 pounds per acre (Figure 1b).

Figure 1. (a) Cover crop green ground cover June 27, Carrington. (b) Cover crop biomass at soybean R2 stage, July 25, Carrington.
Abbreviations: WR = winter rye; WB = winter barley; Cm = winter camelina; Mix = WR+WB+Cm; Check: = no cover crop; 66 = 66% of recommended cover crop seeding rate; 33 = 33% of recommended cover crop seeding rate; R2 = cover crop termination date at soybean R2 stage; No = no termination for cover crop.

Soybean grain yield varied across treatments with spring-planted cover crops. Winter camelina, barley, and rye outperformed the check plot (no cover crop) by 2-3 bushels per acre, representing a 5-8% increase (Figure 2). However, these differences were not statistically significant. Nonetheless, these results provide a promising foundation for refining cover crop seeding rates and termination timing. In the context of North Dakota's agricultural industry, a 5-8% increase in soybean yield could have significant economic implications. In Figure 2, soybean yields may decline further if the cover crop seeding rate exceeds 33% of the recommended rate and/or if cover crops are terminated after the soybean R2 growth stage. 

Figure 2. Soybean grain yield under different cover crop treatments, Carrington.
Abbreviations: WR = winter rye; WB = winter barley; Cm = winter camelina; Mix = WR+WB+Cm; Check: = no cover crop; 66 = 66% of recommended cover crop seeding rate; 33 = 33% of recommended cover crop seeding rate; R2 = cover crop termination date at soybean R2 stage; No = no termination for cover crops.

These findings are a valuable starting point for optimizing cover crop seeding rates and termination timing for soybean production, adding crop diversity, and improving soil health without decreasing soybean yield. However, further research is needed to draw reliable conclusions.

Acknowledgments: The North Dakota Soybean Council supported and funded this project. This work was a collaborative effort with Larry Cihacek, Ph. D.; Szilvia Yuja; and Naeem Kalwar.