Impact of predicted climate scenarios and cropping systems on crop yield and weed communities

Background/Question/Methods Crop yield is influenced by agricultural practices as well as biological and environmental stressors. We compared winter wheat yields and weed communities across three framing systems and contrasting climate conditions at the Fort Ellis Research Farm near Bozeman, MT. Farming systems included a conventional no-till system that relies on chemical inputs for nutrient and weed management (conventional), an organic farming system reliant on tillage for weed control and cover crop termination (tilled-organic), and an organic system that uses sheep grazing to control weeds and terminate cover crops (grazed-organic). Environmental treatments included ambient climate condition, a hotter climate condition that was created using open-top chambers that increased temperatures ~2C, and a hotter and drier climate condition that was achieved using open-top chambers and rain-out shelters that block approximately 50% of precipitation. We modeled the response variables using generalized linear mixed-effects models, and used ANOVA and post-hoc Tukey tests to determine if farming systems and climate conditions caused variation in yields. Multivariate analysis was used to compare weed communities across cropping systems and climate conditions.

Results/Conclusions Under ambient conditions, winter wheat yield varied by farming system with yields similar between the conventional (5.7 t/ha) and tilled-organic systems (5.1 t/ha; P=0.37), and lowest in the grazed-organic system (3.1 t/ha; P<0.001). Wheat yield in the hotter and drier climate condition declined 46% (P=0.02) when compared to the ambient conditions in the conventional farming system. In contrast, wheat yield in the tilled-organic system and the grazed-organic system remained at 99% and 89% relative to ambient under the hotter and drier conditions (P=0.17 and P=0.14, respectively). Weed biomass and number of weed species was highest in the grazed-organic system (14.4 g and 4.4 species per plot; P=0.08 and P=0.03, respectively), and lowest in the conventional farming system (0.60 g and 0.4 species per plot) and the tilled-organic system (3.8 g and 1.5 species per plot). Climate did not influence the number of weed species (P=0.96) or weed biomass (P=0.87) but impacted individual species seed production. Weed community composition varied in response to farming system (P=0.001, R²=0.28), but not in response to climate conditions (P=0.77, R²=0.02). Overall, our initial results indicated that there could be more resilience within organic systems to increased temperatures and lower moisture, and B. tectorum could be a better competitor against winter wheat under hotter and drier climate conditions.