Management options for potential 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, do not provide options for yearlong vegetation. The management of these annual cover crops tend to leave the soil exposed at periods of heavy rainfall, particularly in the early spring. Research is being conducted at the University of Minnesota to discover perennial cover crop species and management options to provide continuous vegetation in corn and soybean rotations. The goal of this research is to grow corn and soybeans in a perennial cover crop to maximize the yield of the cash crop while maintaining continuous living Thus, fully harnessing the environmental benefits of perennials in annual crop rotations. This will be done by combining localized desiccation with broad suppression of the perennial cover crops to minimize early season competition.
Species and management evaluation
The study was conducted at three locations: Rosemount, Waseca, and Lamberton, MN. Perennial cover crop species chosen are two fine fescue species (chewings fescue and hard fescue) and three perennial legumes (kura clover, crown vetch, and a clover mix). The fescues chosen are summer dormant, winter hardy and can tolerate Poast herbicide. The chosen perennial legume species compete minimally, if at all, for fertilizer resources, tolerate defoliation, and spread by rhizomes. To manage these species while simultaneously growing the cash crops corn and soybean, two techniques were employed: zone seedbed preparation for the cash crop to be planted into and in-season chemical suppression of the perennial cover (Bartel et al., 2017).
The seed bed 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 (Photo 2) or chemical desiccation in bands using glyphosate (Photo 3). The perennials were suppressed during the growing season to minimize competition with the cash crops. Low rates of glufosinate (1.48 lb/ac) were applied in late May and mid-June to suppress the perennials. Each plot was fertilized according to best management practices for corn and soybeans and the study was managed weed free through the chemical suppression of the perennials and hand weeding.
Figure 1. Corn yields (bu/ac) grown with perennial cover crops in Lamberton, MN. Band killed prepared seed beds are represented by red bars; rotary zone stripped seed prepared seed beds are represented by blue bars.
Figure 2. Soybean yields (bu/ac) grown with perennial cover crops in Lamberton, MN. Band killed prepared seed beds are represented by red bars; rotary zone stripped seed prepared seed beds are represented by blue bars.
Corn and soybean yield results from the Lamberton location are shown in Figures 1 and 2. For corn, the top average yield from this trial was in the rotary zone stripped crown vetch plots (227 bu/ac), over-yielding the conventional check (222 bu/ac). The band killed fescue cover crops performed the poorest, taking an 89% yield hit from the conventional, no cover check whereas the strip tilled fescue took an average of a 55% yield hit. However, while this yield hit is attributed to heavy competition for light and nutrients, particularly in early June, the hit is 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 bu/ac) which were comparable to the no cover check average of 48 bu/ac. Similar to the corn study, soybeans corn in herbicide killed hard fescue plots performed the poorest (21 bu/ac). Overall, competition with perennial cover crops was minimized using the rotary zone tillage techniques in the soybean study. Further work will be done to explore the persistence of the perennial cover crop species over time. This work will provide growers with options that reduce cost of seed and increase the amount of time roots are living in the soil to prevent erosion and nutrient loss.
These results suggest there is potential to grow corn and soybeans with perennial cover crops. While there is a yield deficit associated with this system, the option of perennial cover crops may be used in highly challenging watersheds and areas of fields subject to heavy erosion. However, more research is needed to continually improve the yields of the cash crops through refining the management techniques of broad suppression and localized desiccation.
Bartel, C. A., C. Banik, A.W. Lenssen, K. J. Moore, D. A. Laird, S.V. Archontoulis, and K. R. Lamkey. 2017. Establishment of Perennial Groundcovers for Maize-Based Bioenergy Production Systems. Agron. J. 109: 822 – 835.