Are polycultures for silage pragmatic medleys or gallimaufries?

Polycultures, mixtures of different crop species in the same field, may provide both production and ecological benefits. Silage production in annual cropping systems may incorporate polycultures and take advantage of species’ niche partitioning, potentially stabilizing yield variation due to abiotic stress. Using maize (Zea mays L.) silage as the basis of our 3-yr study, we tested the impact on crop and soil attributes of replacing a fraction of maize with soy [Glycine max (L.) Merr.], sorghum (Sorghum bicolor var. bicolor × bicolor and var. sudanense [unnamed hybrid]), or a medley of soy, sorghum, and sunflower (Helianthus annuus L.). Compared to maize monocultures and on average for the 3 yr, a replacement mixture of maize + soy lowered yields (1.57 vs. 1.87 kg m^–2), but increased the N, P, and K concentration in the silage by 1.2x, 1.09x, and 1.03x, respectively. Maize + sorghum polycultures matched the biomass yields of maize monocultures (1.77 vs. 1.87 kg m^–2) and increased K concentration (10.2 vs. 8.2 g kg^–1). While random forest analysis revealed no change in post-harvest soil mineral N with depth among treatments, there was a tendency for higher total mineral N left in the soil for soy-containing vs. sorghum-containing treatments (12.4 vs. 10.9 g m^–2). Silage polycultures are a feasible alternative to maize silage monocultures and can improve silage nutrient concentration with no yield penalty if maize or sorghum dominate plant stands.