Search

Adequate seed production is essential for cultivar success in perennial ryegrass turf and forage industries, but improvement is limited by the complexity of yield components and low‐rank correlations between selection and production environments. This study examined seed yield components among 20 perennial ryegrass entries in both spaced plantings (selection environment) and swards (production environment) at two locations in Minnesota. Competitive (23 plants/m²) and non‐competitive (3 plants/m²) spaced‐plant nurseries were tested. Competitive spaced‐plant total yield was highly correlated with sward yield (rₛ = 0.64 and 0.66, p

Diversity and nitrogen addition have positive relationships with plant productivity, yet climate-induced changes in water availability threaten to upend these established relationships. Using long-term data from three experiments in a mesic grassland (ranging from 17 to 34 yr of data), we tested how the effects of species richness and nitrogen addition on community-level plant productivity changed as a function of annual fluctuations in water availability using growing season precipitation and the Standardized Precipitation-Evapotranspiration Index (SPEI). While results varied across experiments, our findings demonstrate that water availability can magnify the positive effects of both biodiversity and nitrogen addition on productivity. These results suggest that productivity responses to anthropogenic species diversity loss and increasing nitrogen deposition could depend on precipitation regimes, highlighting the importance of testing interactions between multiple global change drivers.

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.

Perennial crops have fewer environmental impacts compared to annual crops, but there are no perennial grains available to replace the annual grains that occupy a majority of U.S. cropland. Here we report grain and biomass yields from an improved breeding population of intermediate wheatgrass (IWG) [Thinopyrum intermedium (Host) Buckworth & Dewey], a perennial grass being domesticated to serve as the first widely grown perennial grain crop. Our objective was to measure grain and biomass yields of this improved grain-type IWG (TLI-C2), a forage variety of IWG (cultivar Rush), and switchgrass (Panicum virgatum L.) in response to N fertilization rates ranging from 0 to 200 kg N ha–¹. TLI-C2 grain yields responded quadratically to increasing N rates in all but one environment, but yields declined at high N rates due to lodging. TLI-C2 grain yields were highest during the first year of fertilization, yielding 961 and 893 kg ha–¹ when fertilized at agronomically optimum nitrogen rates (AONRs) of 61 and 96 kg N ha–¹ for stands seeded in fall of 2011 and spring of 2012, respectively. Grain yields declined with stand age. When fertilized with AONRs for grain, biomass yields of TLI-C2 harvested after grain ranged from 9.2 to 12.3 Mg ha–¹ and had similar forage and bioenergy quality characteristics compared to Rush, which demonstrates the potential to manage TLI-C2 as a dual-use cropping system for both grain and forage.

Native perennial bioenergy crops can mitigate greenhouse gases (GHG) by displacing fossil fuels with renewable energy and sequestering atmospheric carbon (C) in soil and roots. The relative contribution of root C to net GHG mitigation potential has not been compared in perennial bioenergy crops ranging in species diversity and N fertility. We measured root biomass, C, nitrogen (N), and soil organic carbon (SOC) in the upper 90 cm of soil for five native perennial bioenergy crops managed with and without N fertilizer. Bioenergy crops ranged in species composition and were annually harvested for 6 (one location) and 7 years (three locations) following the seeding year. Total root biomass was 84% greater in switchgrass (Panicum virgatum L.) and a four-species grass polyculture compared to high-diversity polycultures; the difference was driven by more biomass at shallow soil depth (0–30 cm). Total root C (0–90 cm) ranged from 3.7 Mg C ha−1 for a 12-species mixture to 7.6 Mg C ha−1 for switchgrass. On average, standing root C accounted for 41% of net GHG mitigation potential. After accounting for farm and ethanol production emissions, net GHG mitigation potential from fossil fuel offsets and root C was greatest for switchgrass (−8.4 Mg CO2e ha−1 yr−1) and lowest for high-diversity mixtures (−4.5 Mg CO2e ha−1 yr−1). Nitrogen fertilizer did not affect net GHG mitigation potential or the contribution of roots to GHG mitigation for any bioenergy crop. SOC did not change and therefore did not contribute to GHG mitigation potential. However, associations among SOC, root biomass, and root C : N ratio suggest greater long-term C storage in diverse polycultures vs. switchgrass. Carbon pools in roots have a greater effect on net GHG mitigation than SOC in the short-term, yet variation in root characteristics may alter patterns in long-term C storage among bioenergy crops.

High yields are a priority in managing biomass for renewable energy, but the environmental impacts of various feedstocks and production systems should be equally considered. Mixed-species, perennial grasslands enrolled in conservation programs are being considered as a source of biomass for renewable energy. Conservation grasslands are crucial in sustaining native biodiversity throughout the US Upper Midwest, and the effects of biomass harvest on biodiversity are largely unknown. We measured the effect of late-season biomass harvest on plant community composition in conservation grasslands in three regions of Minnesota, USA from 2009 to 2012. Temporal trends in plant species composition within harvested grasslands were compared to unharvested grasslands using mixed effects models. A before-after control-impact approach using effect sizes was applied to focus on pre- and postharvest conditions. Production-scale biomass harvest did not affect plant species richness, species or functional group diversity, nor change the relative abundance of the main plant functional groups. Differences in the relative abundances of plant functional groups were observed across locations; and at some locations, changed through time. The proportion of non-native species remained constant, while the proportion of noxious weeds decreased through time in both harvested and unharvested grasslands at the central location. Ordination revealed patterns in species composition due to location, but not due to harvest treatment. Therefore, habitat and bioenergy characteristics related to grassland plant communities are not expected to change due to short-term or intermittent late-season biomass harvest.