Cover Crop Mixtures Grown for Annual Forage in a Semi-Arid Environment

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 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, spring-planted mixtures yielded 30 to 60% more forage (2400 kg dry matter ha(-1), 3 yr avg) than the average of spring-planted 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 (94-155 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. Species mixtures affected nutritive value. Grassdominated mixtures had lower crude protein and greater fiber concentrations than radish-dominated mixtures. 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.