Is interannual grain yield decline of intermediate wheatgrass influenced by management and climate in the Upper Midwest?

Perennial crops have the potential to provide sustainable food production while promoting multiple ecosystem services. Intermediate wheatgrass (IWG) is a perennial grass that is currently being domesticated as a perennial grain crop. However, one major hurdle limiting producer adoption is its interannual grain yield decline. While such a phenomenon has an evolutionary basis and has been reported in other perennial grain crops, there are currently conflicting reports about the extent of this phenomenon in IWG. To address this challenge, we have assembled a unique dataset integrating 13 field experiments conducted by the same research team in Minnesota, USA where IWG yield trials were established over 3-4 years, covering 24 location-years representing 9 treatments and up to 3424 plot-level yield observations. Our goals were to 1) determine the extent and magnitude of IWG yield decline and 2) examine the relative contribution of crop management and climate in mitigating IWG yield decline if it exists. Our results indicate that IWG grain yield decline starts during the second production year in Minnesota and continues annually at an average rate of 200-225 kg ha-1 yr-1, driven by a reduction in harvest index which declined at a rate of 2% yr- 1. This decline occurred regardless of crop management practices, but some approaches, particularly optimal nitrogen application, plant density and cultivar choice increased grain yield potential. IWG productivity was also influenced by environmental gradients, with the strongest effect attributable to rising atmospheric drought or vapor pressure deficit (VPD), which influenced yield decline locally. Overall, the analysis indicated that optimal management, in concert with breeding towards more productive and climate-resilient varieties have the potential to reduce IWG decline in Minnesota.