Agronomic advances in Kernza research

Craig Shaeffer, Extension forage agronomist, and Jake Jungers, Department of Agronomy and Plant Genetics

Kernza® is the commercial name of seed harvested from Intermediate wheatgrass (IWG) (scientific name Thinopyrum intermedium), a new perennial grain. The grain can be used as a substitute for annual grains like wheat for production of baked goods, breakfast cereals, and snack bars. Kernza has also been fermented for beer production. More information on development and commercialization of Kernza can be found at https://kernza.org/kernzacap/ and https://forevergreen.umn.edu/crops/kernza-intermediate-wheatgrass. Other technical resources for Kernza production can be found at https://sustainablecropping.umn.edu/resources

Production potential and strategies to reduce yield decline

Figure 1. Between-row mechanical tillage in the
fall has reduced intermediate wheatgrass grain
yield decline.

Kernza grain yields are maximized the year following fall seeding and can exceed 600 pounds per acre. Results from experiments suggest that yields could reach 1000 pounds per acre under ideal growing conditions and management. However, yields decline as much as 50% by the third year. This is due to increases in plant density within the field resulting from IWG tillering, rhizomatous growth, and development of seedlings from shattered seed. Competition among plants for light, nutrients, and moisture reduces yields. 

Our research has shown that between-row tillage in the fall and herbicide application in spring in 3 year old stands increased yields by about 18% compared to the untreated control (Figure 1). However, even with this improvement, average yields of about 200 pounds per acre represented about a 70% decline compared to the first year of production. This indicates the greater potential of plant breeding to change plant morphological development to reduce yield decline.

Seeding dates

Figure 2. Late summer planting date effects on Kernza
grain yield the following spring at St. Paul.

Cooler temperatures and favorable moisture levels in late summer and early fall are beneficial for establishment of intermediate wheatgrass. Research at St. Paul, MN and Roseau, MN showed that planting in early to mid-August provided the best IWG establishment, largest plants at the onset of winter, and greatest first year grain yields (Figure 2). October 15 and October 1 appears to be the final date in southern Minnesota and Roseau, respectively, for economical grain yields because it allowed for morphological development of plants with at least three leaves. 

 No harvestable grain was produced from spring seedings, substantiating that appropriate vernalization and photoperiod requirements are needed for flowering. These results highlight the practical challenges of seeding intermediate wheatgrass for grain production following soybean or corn harvested in October or later. Intermediate wheatgrass can be seeded in spring but will not produce grain until the year following seeding.

Vernalization and photoperiods

Vernalization (derived from latin word Vernus for spring) is a natural process in which development of flowering seed heads of winter grasses is stimulated by winter soil temperatures of 40 F or below for at least six weeks. This is facilitated by the short daylength (photoperiod) of winter. After vernalization, flowering is further promoted by a spring daylength (photoperiod) between 13 and 14 h.

Intermediate wheatgrass successfully remediates soil water N

Intermediate wheatgrass produces short rhizomes and a deep, fibrous root system that supports winterhardiness and year-round ground cover. Ecosystem services provided by IWG include reduced nutrient leaching, decreased soil erosion, and improved soil health. 

Research at the Central Lakes College in Staples, MN on sandy soils prone to N leaching show the value of intermediate wheatgrass to remediate soils that are high in nitrate-N. Average soil nitrate-N in the top 24 inches of the soil was 200 times greater for the annual cropping system compared with intermediate wheatgrass (Figure 3). This was related to the active root system of intermediate wheatgrass which - when averaged over all depths - was 6.1 tons per acre while root biomass of annual crops in a corn-soybean rotation was 82% lower (1.1 ton per acre; Figure 4). To take advantage of Intermediate wheatgrass’ capability to remediate soils with unsafe levels of nitrate, it has been deployed at several other wellhead production sites to reduce nitrate-N leaching to drinking water.

Figure 3. Average nitrate-N in the soil at four depths  beneath a corn and soybean rotation and IWG after  three years of production in Staples, MN.

Figure 4. Root biomass of an annual crop (soybean) and intermediate wheatgrass (IWG) at four depths.

Soil health benefits of IWG

Figure 5. The effect of perennial crops (IWG; IWG
 intercropped with alfalfa (IWG+Alfalfa); alfalfa) and
 annual corn and soybean grown in rotation with a
 cover crop (Corn-CC-Soybean) and without on soil
 macroaggregates.

The extensive root system of intermediate wheatgrass adds a significant amount of organic matter to the soil. This organic matter provides fuel for soil microbes and on some soils, soil health and water infiltration have improved as a result of IWG production. 

When IWG was grown for two years as part of an organic transition program, IWG did not consistently affect soil bacterial and fungi populations, likely due to the short duration of the experiment. However, IWG did affect soil aggregation (Figure 5), where IWG grown alone and with alfalfa had greater fraction of large soil aggregates than annual soybean-corn rotation with and without winter cover crops.

Summary

Kernza is being developed as a grain crop that will provide both economic return and ecosystem services. Agronomic management strategies are being developed to increase the profitability of production. Research on many aspects of Kernza breeding and management is being facilitated by the Kernza CAP project https://kernza.org/kernzacap/.

References for further reading

Bajgain, P.; Zhang, X.; Jungers, J.M.; Dehaan, L.R.; Heim, B.; Sheaffer, C.C.; Anderson, J.A. ‘MN-Clearwater’, the first food-grade intermediate wheatgrass (Kernza perennial grain) cultivar. J. Plant Regist. 2020, 14, 288–297. https://doi.org/10.1002/plr2.20042.

Bergquist, G.; Gutknecht, J.; Sheaffer, C.; Jungers, J.M. Plant Suppression and Termination Methods to Maintain Intermediate Wheatgrass
(Thinopyrum intermedium) Grain Yield. Agriculture 2022, 12, x. https://doi.org/10.3390/xxxxx

Puka-Beals, J.; Sheaffer, C.C.; Jungers, J.M. Forage yield and profitability of grain-type intermediate wheatgrass under different harvest schedules. Agrosystems Geosci. Environ. 2022, 5, e20274. http://doi.org/10.1002/agg2.20274.

Rakkar, M., Jungers, J. M., Sheaffer, C., Bergquist, G., Grossman, J., Li, F., & Gutknecht, J. L. (2023). Soil health improvements from using a novel perennial grain during the transition to organic production. Agriculture, Ecosystems & Environment, 341, 108164.

Reilly EC, Gutknecht JL, Sheaffer,CC and Jungers JM (2022) Reductions in soil water nitrate beneath a perennial grain crop compared to an annual crop rotation on sandy soil. Front. Sustain. Food Syst. 6:996586. doi: 10.3389/fsufs.2022.996586