Intercropping Red Clover with Intermediate Wheatgrass Suppresses Weeds Without Reducing Grain Yield

Project Director: Eugene Law, Cornell University

Project Overview

Intermediate wheatgrass (IWG), commonly referred to as ‘Kernza,’ is the first perennial grain crop to be grown commercially in the United States. In recent years, it has gained attention within the agricultural community for its potential as an environmentally sustainable, dual-purpose (grain and forage) crop.

Due to its recent introduction to the U.S. agricultural market, there is still much to be learned about Kernza, including its impacts on weed suppression/weed community structure, and its performance when intercropped with legumes. This study, conducted over three years at the Cornell University Musgrave Research Farm, evaluated grain/straw yields, fertility, and weed dynamics for Kernza and hard red winter wheat (an annual grain crop) when grown independently and when intercropped with a medium red clover.

Farmer Takeaways

Intermediate wheatgrass (‘Kernza’) holds potential as a dual-purpose (grain/forage) crop. Farmers may benefit from transitioning Kernza from grain to forage production after the first year of establishment due to observed physiological changes in the crop that result in significant grain yield declines after Year 1.
Kernza may be a more viable forage crop than annual small grains such as red winter wheat. Given its high forage production and soil health benefits, Kernza may be a particularly viable crop in regions where livestock are prevalent or in integrated crop-livestock systems.
Intercropping red clover may be a highly effective, NOP-compliant weed suppression strategy for both annual and perennial grain crop systems, including Kernza.

Project Objectives and Approach

Evaluate the grain and forage productivity of Kernza relative to winter wheat, with and without red clover

A three-year study was conducted between 2016 and 2019 at the Cornell University Musgrave Research Farm. Main plot treatments included: (1) Kernza intermediate wheatgrass and (2) hard red winter wheat (cultivar Warthog). Split-plot treatments included: (1) interseeded medium red clover and (2) a no-clover control. Soil and crops were managed organically according to the USDA National Organic Program regulations; however, the field was not certified organic.
- Both grain crops were planted in late August during Year 1 (with subsequent annual plantings of red wheat), and red clover was interseeded into respective plots in March.
Grain was harvested annually from all plots, and and a sample of plants from each plot were evaluated for # of tillers, fertile tiller percentage, seedhead length and weight, floret count, seed count, and seed weight. Total grain yields were estimated.
1-2 weeks after grain harvest, forage was harvested by cutting aboveground biomass above 10cm. Total forage yields were calculated; for the plots interseeded with red clover, the combined clover and Kernza/red wheat forage biomass was used for the total forage yield calculation.

Assess the impacts of Kernza and winter wheat, both with and without red clover, on weed community structure and biomass

Weed biomass samples were collected from quadrats in each plot at the time of crop maturity, which varied by crop type. Total weed biomass was estimated, and weed community structure (weed species, species richness, and species evenness) was evaluated for each plot.

Key Findings

Kernza grain yields were significantly lower than red wheat grain yields and experienced a significant decline after Year 1, influenced in part by a decline in tiller fertility and seed count.

Red winter wheat produced 487% more grain than Kernza over the three-year study period.
Kernza grain yields were highest in Year 1, then experienced significant declines in Years 2 and 3 (1,212 kg/ha, 202 kg/ha, 441 kg/ha, respectively). This finding aligns with results from previous Kernza studies, although the exact mechanism(s) behind this yield decline are not yet understood.
- Despite experiencing an increase in total # of tillers/plant between Years 1 and 3, a smaller proportion of the total tillers contained seedheads (were ‘fertile’) each year, resulting in a decrease in Kernza tiller fertility from 79% in Year 1 to 57% in Year 3. This suggests that Kernza may dedicate fewer resources to reproductive structures over time.
- Kernza also experienced a decline in seedhead weight and seed count at harvest, contributing to the smaller grain yields observed in Years 2 and 3.
Red winter wheat grain yields experienced slight declines between Years 1 and 3 (3,429 to 2,416 kg/ha, respectively), although these declines were not statistically significant.

Kernza forage yields were higher than for red wheat and experienced an increase between Years 1 and 3.

In contrast to the declines in grain yield, Kernza experienced an increase in forage yields between Years 1 and 3 (5,541 to 7,785 kg/ha, respectively), suggesting that Kernza may dedicate more resources to non-reproductive structures over time.
Red wheat forage yields were highest in Year 1 (5,167 kg/ha) than in Years 2 or 3 (3,072 and 3,533 kg/ha, respectively), and were consistently smaller than Kernza forage yields.

Red clover, when intercropped with Kernza and red winter wheat, may provide significant weed suppression by reducing total weed biomass and weed species richness.

Averaged over the three-year study period, total weed biomass for intercropped Kernza/clover plots was significantly lower than for monoculture Kernza plots (445 vs. 1,216 kg/ha, respectively). Similarly, total weed biomass for intercropped red wheat/clover plots were lower than for monoculture red wheat plots (349 vs. 434 kg/ha, respectively).
- Total weed biomass was significantly higher in Kernza plots than red wheat plots in Years 1 and 2.
- Red clover biomass was significantly higher (244%) in Kernza plots than red wheat plots.
Intercropping red clover did not have a significant impact on either Kernza or red wheat grain yields, highlighting red clover’s potential as a low-risk, high-impact weed suppression strategy for both annual and perennial grain crops.

Weed community structure may be influenced by crop species (Kernza vs. red wheat) and intercropping (red clover vs. monoculture).

At the beginning of the study period, all plots supported a mix of both annual and perennial weeds. However, by Year 2, ~90% of the weed biomass in Kernza plots were perennial weeds, indicating that weed community composition may be significantly impacted by crop type, particularly between annual vs. perennial crop types.
The percentage of total weed biomass occupied by perennial weeds increased from 30.2 – 77.2% in plots intercropped with red clover.

Resources

Law, E.P., S. Wayman, C.J. Pelzer, A. DiTommaso, and M.R. Ryan. 2021. Intercropping red clover with intermediate wheatgrass suppresses weeds without reducing grain yield. Agronomy Journal 114:700-716. https://doi.org/10.1002/agj2.20914.

Location

New York

Collaborators

Sandra Wayman, Cornell University
Christopher Pelzer, Cornell University
Antonio DiTommaso, Cornell University
Matthew Ryan, Cornell University

Region

Northeast/Mid-Atlantic

Topic

Soil Health, Crop Nutrient Management, Weed Management, Climate Solutions, Transitioning to Organic, Cropping Systems

Year Published

2021