Intermediate wheatgrass (Thinopyrum intermedium; IWG), a new perennial grain crop, has the potential to provide ecosystem services while producing food-grade grain; however, productivity is currently limited by high rates of lodging. Trinexapac-ethyl (TE) and prohexadione-calcium (PC) are widely used plant growth regulators (PGRs) for mitigating lodging and improving seed yield in other grass crops. Our objectives were to determine the effects of the PGRs PC and TE, PGR application rate, and nitrogen (N) fertilizer rate (0, 40, 80 kg N ha–1) on IWG lodging, height, and grain and biomass yields. Experiments were initiated in first- and third-year stands at St. Paul and Rosemount, MN. Few effects of PC on IWG height, lodging, or yields were observed, while TE consistently reduced plant height by 10 to 20% and lodging by up to 20% in a year with high lodging risk. Application of TE to IWG at the recommended rate (437 g a.i. ha–1) or higher rates increased grain yields by 65 to 100% when lodging incidence was high, but did not affect grain yields in years with lower lodging risk. While a negative correlation between lodging and grain yields was observed, nitrogen fertilizer affected IWG grain and biomass yields in only one of five site-years, and there was no interaction between N fertilizer and PGR effects on IWG. Nonetheless, the PGR TE demonstrated the potential to reduce plant height and lodging, thereby increasing IWG yield potential.
Bibliographical noteFunding Information:
Much gratitude to Donn Vellekson and Joshua Larson for their input and help with this study. Thanks also to the anonymous reviewers who contributed enormously to this manuscript. This work was funded by the University of Minnesota’s Forever Green Initiative. This work was also supported by The Perennial Agriculture Project, a joint project of The Malone Family Land Preservation Foundation and The Land Institute.
© 2018 by the American Society of Agronomy.