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Species diversity can increase natural grasslands productivity but the effect of diversity in agricultural systems is not well understood. Our objective was to measure the effects of species composition, species richness, and harvest management on crop and weed biomass in perennial herbaceous polycultures. In 2003, 49 combinations of seven species (legumes, [C.sub.3] and [C.sub.4] grasses) including all monocultures and selected two to six species polycultures were sown in small plots at two Iowa, USA, locations in a replicated field design. Plots were split in half and managed with either one or three harvests in each of 2004 and 2005. Biomass increased log-linearly with species richness in all location-management environments and the response was not different between managements. Polycultures outyielded monocultures on average by 73%. The most productive species in monoculture for each management best explained the variation in biomass productivity. The biomass of plots containing this species did not increase with richness in most environments but biomass of plots without this species increased log-linearly in all cases. Weed biomass decreased exponentially with richness in all environments. On average, increasing species richness in perennial herbaceous polycultures increased productivity and weed suppression, but well-adapted species produced high biomass yield regardless of richness.

Kernza® intermediate wheatgrass (Thinopyrum intermedium) is a novel perennial grain and forage crop with the potential to provide multiple ecosystem services, which recently became commercially available to farmers in the USA. The viability and further expansion of this promising crop require understanding how it may fit the needs of farmers' livelihoods and the structure of their farming systems. However, no prior research has studied the perceptions and experiences of Kernza growers. The goals of this research were to understand why farmers grow Kernza, how Kernza fits into their systems and identify challenges for future research. We conducted in-depth interviews with ten growers in the North Central USA during the summer of 2017, who accounted for a third of the Kernza farmers in the USA at the time. All farmers had a positive attitude toward experimentation and trying new practices, and they were interested in Kernza for its simultaneous ecological and economic benefits. Kernza was marginal in terms of area, quality of fields and resources allocated in the farm systems, which also meant that farmers maintained low costs and risks. Growers utilized and valued Kernza as a dual-use crop (grain and forage), sometimes not harvesting grain but almost always grazing or harvesting hay and straw for bedding. Weeds were perceived as a challenge in some cases, but Kernza was valued as a highly weed-suppressive crop in others. Farmers requested information on optimal establishment practices, assessment of forage nutritive value, how to maintain grain yields over years, weed management, markets and economic assessment of Kernza systems. These results agree with other cases on sustainable practices adoption showing that engaging farmers in the research process from the beginning, identifying knowledge gaps and testing management alternatives are critical for the success and expansion of novel agricultural technologies. [ABSTRACT FROM AUTHOR]