Perennial cover crops

University of Minnesota research suggests there’s potential to grow corn and soybeans with perennial cover crops. While there’s a yield deficit, perennial cover crops may be an option in highly challenging watersheds and field areas subject to heavy erosion.

However, more research is needed to maximize cash crop yields by minimizing early-season competition from the perennial covers.

Why study perennial cover crops

From soil stabilization to nutrient capture, the benefits of cover crops are abundant.

Yet, the most common cover crops, such as rye, radish mixtures or hairy vetch, don’t provide options for yearlong vegetation. Managing these annual cover crops tends to leave the soil exposed at periods of heavy rainfall, particularly in the early spring.

Research on perennial cover crops

To hopefully enable continuous vegetation in corn and soybean rotations, University of Minnesota researchers are trying to discover perennial cover crop species and management options.

The research aims to grow corn and soybeans in a perennial cover crop to maximize the yield of the cash crop, while maintaining continuous living. This would fully harness the environmental benefits of perennials in annual crop rotations.

Evaluating species and management techniques

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The perennial cover crop species chosen were two fine fescue species (chewings fescue and hard fescue) and three perennial legumes (kura clover, crown vetch and a clover mix).

The chosen fescues are summer-dormant and winter-hardy, and can tolerate Poast herbicide. The chosen perennial legume species minimally compete, if at all, for fertilizer resources, tolerate defoliation and spread by rhizomes.

To manage these species while simultaneously growing the corn and soybean cash crops, they deployed two techniques: Zone seedbed preparation for the cash crop to be planted into and in-season chemical suppression of the perennial cover.

The seedbed preparations were applied in the late fall, following harvest of the cash crop. These techniques were either a manual killing of the perennial using rotary zone tillage (Figure 2) or chemical desiccation in bands using glyphosate (Figure 3).

The perennials were suppressed during the growing season to minimize competition with the cash crops. Researchers applied low rates of glufosinate (1.48 pounds per acre) in late May and mid-June to suppress the perennials.

Each plot was fertilized according to best management practices for corn and soybeans. The study was managed weed-free through chemically suppressing the perennials and hand weeding.

Figure 2: Rotary zone tillage for seedbed preparation.

Figure 3: Chemical-applied strips for seedbed preparation.

Yield results

Figures 4 and 5 show corn and soybean yield results from the Lamberton location.

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For corn, the top average yield from this trial was in the rotary-zone-stripped crown vetch plots (227 bushels per acre), over-yielding the conventional check (222 bushels per acre).

The band-killed fescue cover crops performed the poorest, taking an 89 percent yield hit from the conventional, no-cover check, while the strip-tilled fescue took a 55 percent average yield hit.

While this yield hit is attributed to heavy competition for light and nutrients, particularly in early June, it’s also due to complications with planting corn and soybean into high-residue environments leading to poor establishment of the cash crop.

Comparing within species, the fescue species and the crown vetch performed best under the rotary zone tillage with suppression while the kura and legume mix cover crop species performed better with chemically applied strips.

Average soybean yields from the Lamberton location were found in the legume mix plots (50 bushels per acre), which were comparable to the no-cover check average of 48 bushels per acre.

Similar to the corn study, soybeans in herbicide-killed hard fescue plots performed the poorest (21 bushels per acre). Overall, using the rotary zone tillage techniques minimized competition with perennial cover crops in the soybean study.

Further work will need be done to explore the persistence of the perennial cover crop species over time. In the meantime, these results provide growers with options that reduce seed costs and increase the amount of time roots are living in the soil to prevent erosion and nutrient loss.