Interplanting crested wheatgrass with shrubs and alfalfa: effects of competition and preferential clipping

Abstract

Planting palatable shrubs and legumes into an established stand of crested wheatgrass (Agropyron desertorum and A. cristatum) could increase forage yield and nutritional quality. Preferential grazing of the grass and legume in spring may enhance establishment of shrub seedlings. Seedlings of 3 species of shrubs (Artemisia tridentata ssp. vaseyana, Kochia prostrata, and Atriplex canescens) were transplanted into plots of crested wheatgrass using a replacement series design. Each species of shrub was grown with the grass, and with the grass and alfalfa (Medicago sativa cv. 'Ladak'); each of the 5 species was also grown in monoculture. Swards were either uncut or the grass and alfalfa were clipped while actively growing in late May and early June. Shrubs had greater current annual growth (CAG) (P is lesser than or equal to 0.001), higher relative yields (P is lesser than or equal to 0.05), lower mortality (P is lesser than or equal to 0.001), and more inflorescences (P≤0.001) in monoculture than in mixture. The grass had greater CAG in mixture than in monoculture (P is lesser than or equal to 0.05), and the grass and alfalfa had greater relative yield in mixture than in monoculture (P is lesser than or equal to 0.05). Clipping crested wheatgrass and alfalfa increased shrub CAG (P is lesser than or equal to 0.01), reduced mortality (P is lesser than or equal to 0.001), and increased the number of inflorescences (P is lesser than or equal to 0.01), but the increase in shrub CAG and flowering due to clipping was not as great as when shrubs were grown in monoculture. There were no interactions between competition and clipping (P>0.05). In terms of CAG, mortality, and flowering, A. tridentata grew better than K. prostrata, which grew better than A. canescens, but these relationships involved complex interactions. The contribution of shrubs to the biomass in mixture was minor; although alfalfa dominated three-way mixture yields, the grass also made a substantial contribution. Since competition was more important in determining shrub response than clipping and the 2 effects were independent, it is probably more important to reduce interspecific competition than to modify grazing practices when planting shrubs in a crested wheatgrass stand.