Should You Use a Single- or Multiple-Species Cover Crop?
There is agreement that cover crops [CC] should be included as a component of a conservation production system [also click here] since their inclusion contributes to enhanced soil health, among other things. In fact, using CC’s is a conservation practice that will accrue carbon [C] credits as part of a C program offered to producers by myriad companies. Click here to access a White Paper on this website that provides details about using CC’s in a conservation production system [CPS].
Since it is accepted that CC’s should be an integral component of a CPS, producers no longer have to be concerned with whether or not using CC’s for conservation purposes is appropriate. However, they do have to be cognizant of the plant species or mixture of species to use to gain the maximum benefit based on their intended goal(s) from CC use and the requirement(s) stipulated in a C contract that they may have.
There are myriad reasons for using CC’s, such as to 1) suppress weeds, 2) remedy or reduce soil compaction, 3) scavenge excess soil nutrients, 4) produce ground cover to prevent erosion, 5) produce biomass to increase soil organic matter [SOM], and 6) add nitrogen [N] to soil, to name a few. Thus, selection of a CC species or species mix should be based on the reason(s) the CC is being used in a particular production system.
The crop following a CC should be considered when selecting a CC species since a legume CC such as vetch or clover will add N to soil that will benefit a following crop such as corn or sorghum, while a grass CC such as cereal rye will likely use excess N in the soil and thus be a candidate as a species to use preceding a legume crop such as soybeans.
Getting and keeping an adequate stand of some CC species can be problematic, and this must be considered when using a species mix–i.e., will one of more of the species in a mix out-compete other species in the mix? Click here to access a CC White Paper on this website that provides details about using CC’s in a CPS.
Below are links to articles that present results from research with mono- and poly-culture CC’s. Following the title of each linked article are the major findings and conclusions from the research reported in that article
Evaluation of single and mixed cover crops species in a sandy loam soil under corn production.
• For corn production in Miss., the use of a CC monoculture of either crimson clover or hairy vetch may be the best option in the short term for initial CC inclusion in a CPS where corn is the summer crop.
• This system needs further research to create more information that includes the effect of termination timing of the CC in relation to early corn planting that occurs in the Midsouth, and the cost of seed of each CC species on the long-term sustainability of inserting either of these legume species in a CPS that includes corn as the following crop.
Do diverse cover crop mixtures perform better than monocultures? A systematic review.
• Overall, there was negligible evidence that a mix of CC species outperformed a single-species CC in terms of the metrics [biomass production, weed suppression, soil nutrient retention, soil N scavenging, soil water and soil biology dynamics, and yield of following crops] evaluated in this study.
• Seeding rate variability of the CC species in mixtures often confounds results among studies that evaluate effects of CC mixtures vs. CC monocultures. When cases of CC mixtures being seeded at elevated rates compared to CC monocultures were excluded from the evaluation, there was no evidence of CC mixtures outperforming CC monocultures on any of the metrics evaluated in this study.
• In 88% of the 243 comparisons used in this review, there was no significant difference between performance of the best CC mixture and the best CC monoculture. In only 2% of the cases used in the evaluation did the best CC mixture outperform the best CC monoculture, and again, the effects of CC mixtures were confounded with the effects of seeding rate.
What are the benefits of a cover crop mix versus a single species cover crop?.
• The decision of whether or not to use a CC species mix or a single CC species will depend on the expected outcome from using the CC, when it will be seeded, when it will be terminated, what crop will follow the CC, and the cost of CC seed in the mix.
• If using a CC mix to achieve multiple goals, all goals may not be fully realized.
• Species in a mix should complement each other, but are very likely to have different optimum planting times and growth and development rates. This can confound achieving the multiple goals that were intended when choosing the CC mix.
• Know before planting a CC mix vs. a single CC species what the optimum termination times are for each species in the mix, and how termination of the species in the mix will be done.
• Each species in a CC mix will only contribute to the overall success of the mix if it produces adequate biomass to accomplish the purpose for its inclusion.
As with all practices used in crop production, there is no “one-size-fits-all” when it comes to selecting a CC species or species mix to use in a CPS. It all goes back to determining the major reason for using a CC in the first place, and then selecting the species or species mix that will best accomplish the intended goal while optimizing economic return from the practice over the long term.
Composed by Larry G. Heatherly, July 2024, larryh91746@gmail.com