Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/24/2017
Publication Date: 3/1/2018
Citation: Sanderson, M.A., Johnson, H.A., Hendrickson, J.R. 2018. Cover crop mixtures grown for annual forage in a semi-arid environment. Agronomy Journal. 110:525-534. https://doi:10.2134/agronj2017.04.0228.
Interpretive Summary: The emerging use of cover crop cocktails (i.e., complex mixtures of functionally diverse cover crops) in diverse cropping systems can improve ecosystem services. We tested whether cover crop mixtures with more equal proportions of species in the seed mixture would have greater productivity and fewer weeds than mixtures dominated by one or two species or monocultures. Our hypothesis that mixtures would yield more than the average of monocultures was supported by data from spring plantings but not late-summer plantings. Mixtures, however, did not produce more forage than the most productive individual monoculture (Triticale). There was little or no support for our hypotheses that mixtures would suppress weeds better than monocultures or that mixtures with equal proportions of species would yield more crop biomass or suppress weeds better than other mixtures or monocultures. Our results indicate that spring-planted cover crops can provide early summer forage, which could be valuable in a grazing and cropping system that includes perennial grassland. Late-summer seeding of cover crops in this region is risky because of lack of rainfall and short growing season and provides little forage production or weed suppression benefit.
Technical Abstract: Use of cover crop mixtures in the dry short-season environment of the northern Great Plains requires knowledge of how species combinations affect productivity and weed invasion. We hypothesized that mixtures would be more productive and suppress weeds better than monocultures. Fifteen combinations of proso millet (Panicum milaceum L), triticale (Triticosecale rimpaui Wittm.), red clover (Trifolium pratense L.), and forage radish (Raphanus sativus L.) were sown in spring (July harvest) and late-summer (October harvest) for 3 yr at Mandan, ND. Treatments included four monocultures, four mixtures dominated by one species, six mixtures dominated by pairs of species, and one equal mixture. On average, mixtures yielded 30 to 60% more forage (2400 kg dry matter ha-1, 3 yr avg) than the average of monocultures (1720 kg ha-1, 3 yr avg) when planted in spring. Mixtures, however, did not yield more forage than the most productive monoculture (triticale; 3165 kg ha-1, 3 yr avg). The late summer planted cover crops produced little forage (94 to 155 kg ha-1) because of dry soil conditions and erratic rainfall. Mixtures with equal proportions of species did not yield more forage or have fewer weeds than other mixtures. Spring-planted cover crops suppressed weeds (compared with a nonplanted control) regardless of mixture or monoculture. Cover crop mixtures can yield more than monocultures when planted in spring in this short-season environment; however, use of cover crop mixtures in late-summer does not mitigate risk of poor establishment and low productivity because of hot dry weather.