Background

The Cover Crop Initiative, a multi-year collaboration between the University of Nebraska-Lincoln (UNL) and the Nebraska Natural Resources Conservation Service (NRCS), promotes the strategic use of spring-, summer- and fall-planted cover crops (CCs) across Nebraska. 

Cover crops offer several potential benefits, including soil erosion control, nitrogen cycling, organic matter build up, weed suppression, and livestock forage. However, their success, particularly in terms of aboveground biomass — a key driver of their ecosystem benefits — is influenced by species selection and adaptation to specific environmental conditions.

In western Nebraska’s semi-arid climate with cold, dry winters and short growing windows, information on the adaptability and productivity of diverse cover crop species is limited. To address this, we evaluated the growth and productivity of 30 commercially available cover crop species, varieties and mixtures planted in fall under the region’s unique climatic conditions.

Study Site, Experimental Design and Treatments

The study was conducted during the 2022-2023 and 2023-2024 growing seasons at the UNL Panhandle Research, Extension, and Education Center (PREEC) in Scottsbluff, Nebraska. The semi-arid site receives a 30-year mean precipitation of 100 mm from September to November (initial growth period) and 290 mm during the full CC growing season (September to May). The soil is classified as Tripp very fine sandy loam with a pH of 8.3. 

The trials followed a randomized complete block design (RCBD) with four replications and plot sizes of 1.5 m × 9.1 m. Cover crops included grasses (11 species), legumes (six species), brassicas (five species), two-way mixtures (five combinations), and three-way mixtures (three combinations). Table 1 lists the species, varieties and seeding rates used. 

The seeding rates were intentionally set higher than those commonly practiced to ensure establishment and growth, facilitating meaningful comparisons among species. Cover crops were seeded in late fall (Sept. 16, 2022 and Sept. 26, 2023) using a research drill at a depth of 3.2 cm. The preceding crops were sunflower in 2022-2023 and field peas/soybean in 2023-2024. 

The trials were conducted under no-tillage, rainfed conditions, with 5.08 cm of irrigation applied in fall 2022 to ensure germination under extremely dry conditions. Termination occurred in early May each year (May 9, 2023 and May 14, 2024) to align with summer cash crop planting schedules (e.g., dry beans, corn, peas, sorghum and sugarbeets).

During the initial growth period, the total precipitation received was 50 mm in fall 2022 and 80 mm in fall 2023. Over the entire growing period, from planting to termination, total precipitation was 225 mm in 2022-2023 and 168 mm in 2023-2024.

Data Collection

Cover crop establishment and productivity were evaluated in the fall and the following spring (six and 33 weeks after planting, respectively). Key metrics included:

• Stand Count: Live upright plants counted within a 0.19 m² quadrant.
• Plant Height: Measured from ground level to the highest fully expanded leaf.
• Ground Cover (%): Estimated using the CANOPEO mobile app.
• Aboveground Biomass Yield: Aboveground biomass collected from a 0.19 m² quadrant, oven-dried at 65°C for one week, and weighed.

Results

2022-2023 Growing Season

Despite camelina failing to establish, early aboveground biomass in the fall (1.5 months post-planting) ranged from 253–689 kg/ha (average: 492 kg/ha) for grasses, 77–361 kg/ha (average: 169 kg/ha) for legumes, 124–382 kg/ha (average: 220 kg/ha) for brassicas, and 218–733 kg/ha (average: 398 kg/ha) for mixtures (Figure 1A).By spring, several species, including both oat varieties, all peas, and brassicas, were winter-killed.

At termination in the spring (7.7 months post-planting), aboveground biomass for surviving species ranged from 84–2,487 kg/ha (average: 1,151 kg/ha) for grasses, 140–337 kg/ha (average: 247 kg/ha) for hairy vetch, and 124–1,993 kg/ha (average: 803 kg/ha) for mixtures (Figure 1A). Top producers included Yankee rye (2,487 kg/ha) and Hazlet rye (2,478 kg/ha), significantly outpacing other treatments,except Elbon rye (1777 kg/ha) and the Elbon rye and AU-merit hairy vetch mixture (1993 kg/ha). Within mixtures, Elbon rye outperformed other grasses in aboveground biomass by more than 164%. Grasses provided the highest ground cover (30.3%), followed by mixtures (23.1%) and hairy vetch (6.7%).

2023-2024 Growing Season

Similar to the previous year, camelina failed to establish. Early-season aboveground biomass in the fall ranged from 172–646 kg/ha (average: 417 kg/ha) for grasses, 68–134 kg/ha (average: 104 kg/ha) for legumes, 72–109 kg/ha (average: 90 kg/ha) for brassicas, and 126–251 kg/ha (average: 189 kg/ha) for mixtures (Figure 1B). By spring, all oat varieties, brassicas, and 4010 pea were winter-killed.

At termination in the spring, aboveground biomass for surviving species were significantly higher compared to the previous year, ranging from 1,100–9,608 kg/ha (average: 4,078 kg/ha) for grasses, 335–1,023 kg/ha (average: 690 kg/ha) for legumes, and 1,013–5,916 kg/ha (average: 2,957 kg/ha) for mixtures (Figure 1B). Elbon rye was the highest-yielding species, producing 9,608 kg/ha, followed by its mixtures with MT hairy vetch (5,916 kg/ha) and AU-merit hairy vetch (5,912 kg/ha). Within mixtures, Elbon rye exceeded other grasses in aboveground biomass by over 80%. Grasses again provided the highest ground cover (56.7%), followed by mixtures (51.4%) and legumes (23.4%).

Key Takeaways

• Rye varieties, particularly Elbon rye and its mixtures, consistently achieved the highest aboveground biomass, showcasing their adaptability to western Nebraska's growing conditions.
• Cold-sensitive species such as camelina failed to establish, while oat, rapeseed, collard, and radish, also cold-sensitive, were winter-killed. However, winter pea varieties, specifically Survivor and WyoWinter, survived one winter.
• In mixtures with legumes or brassicas, Elbon rye outperformed other grass species in aboveground biomass.
• Greater ground coverage was positively associated with higher aboveground biomass across both growing seasons.