Intermediate wheatgrass (Thinopyrum intermedium) (IWG) is a perennial grass being domesticated for grain production with potential to provide economic return and ecosystem services across a broad geographic range in North America, yet optimum seeding dates for grain and biomass yield are unknown. Our objective was to determine the effect of late‐summer, fall, and spring seeding dates on grain and biomass yield of a grain‐type IWG population. Trials were conducted at St. Paul and Roseau, MN, Kalispell, MT, and Salina, KS. Seeding dates ranged from August to June of the following year. Grain and biomass yields were highest when seeded at the earliest late‐summer date for all environments except for Kansas, where a September 29 seeding date produced the greatest grain and biomass yields. Little to no grain was produced from spring seedings in the first production year, substantiating that photoperiod and vernalization requirements are needed for seed head induction. Grain and biomass yields were positively correlated to cumulative growing degree days (GDD) from seeding date to winter dormancy. A quadratic response was observed at Salina, KS, where seed yields maximized when GDD accumulation reached 912. Accumulation of vernalization units throughout fall, winter, and spring after seeding was also positively correlated with grain yield. The minimum vernalization units for grain production varied from 50 to 87 across sites. Results highlight important associations between thermal units and IWG grain yield when seeded in late summer; however, other variables affecting IWG seed head induction (e.g., photoperiod, snow cover) require further study.

Silflower (Silphium integrifolium Michx.) is a potential perennial oilseed crop that can provide ecosystem services; however, its seed, oil, and biomass yield potential are unknown. Our objectives were to determine the effects of planting density and N fertilizer on silflower seed, oil, and biomass yields and seed yield components for 3 yr after establishment. Experiments tested six planting densities on two soil types, and five N rates and two planting densities on one soil type. Averaged over years and soil types, increasing planting density from 11,954 to 53,792 plants ha −1 increased biomass yield (BY), but decreased seed heads plant −1 and seeds plant −1. Planting density had no effect on seed yield (SY) or oil yield (OY), other seed related variables, or harvest index. On a sandy soil, SY and OY increased linearly with N rates from 0 to 180 kg ha −1 in the year after seeding but were not affected by N fertilization rates in subsequent years. At 180 kg N ha −1 , SY, OY, and BY were 1,651 kg ha −1 , 381 kg ha −1 , and 10.5 Mg ha −1 , respectively, in the year following seeding but declined thereafter. Over both experiments SY and OY were positively correlated (r = .99) and together associated with seed heads plant −1 , seeds head −1 , and seeds plant −1. Relative to annual oilseed crops, seed and oil yields for this new perennial species are low. Germplasm improvement for seed and oil yield and agronomic research to maintain yields as stands age are critical to develop this new perennial oilseed crop. 1 INTRODUCTION Annual crops such as soybean [Glycine max (L.) Merr.], sunflower (Helianthus annuus L.), and canola (Brassica napus L.) dominate the oilseed markets in the Midwest region of the Abbreviations: BY, biomass yield; HI, harvest index; HSW, hundred seed weight; OY, oil yield; SHP, number of seed heads per plant; SOC, seed oil content; SPP, number of seeds per plant; SSH, number of seeds per seed head; SY, seed yield; WSH, weight of seed per seed head. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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