Multi-Species Cover Crops in Fallow-Wheat No-Till Systems in Montana.

Single-species legume green manure (LGM) cover crops have shown promise in mitigating the negative effects of summerfallow and improving biological soil quality indicators such as microbial biomass and soil enzyme activity in the semiarid Northern Great Plains (NGP). Recently, farmers in the NGP have been experimenting with multi-species cover crops, or cover crop mixtures (CCMs), in no-till wheat-fallow rotations in response to anecdotal claims that a diverse CCM may stimulate greater soil biological activity than a single species LGM crop. Our research investigates the effects of CCM’s on soil physical, chemical, and biological properties, along with subsequent-year crop productivity. Two field sites were established in 2012, where we grew eight species of cover crops from four plant functional groups (legume, grass, brassica, tap root), either singly or in combination. CCMs were compared with both fallow and single-species pea controls.  Results from 2012 indicate that some of the CCMs (generally oat-containing) produced 0.28 Mg/ha greater biomass than the single-species pea treatment at one of two sites (P<0.01). Care must be taken in interpreting biomass results due to the substitutive design of the study. Soil biological parameters were measured in soils sampled prior to spring wheat seeding, to determine whether any differences in soil communities following CCMs persisted. Soil enzymes showed no significant difference among fallow, pea, and full eight-species CCM after one cover crop year. In 2013, these sites were planted with spring wheat, and two additional cover crop sites were established. Soil biological results from 2012 and biomass yield and wheat yield results from the 2013 trials will be presented.