Optimizing Spring Wheat Sowing Windows in Idaho: Integrating Growing Degree Days and Crop Modeling to Improve Yield Stability

Commodities

• Agronomic: wheat

Practices

• Crop Production: cropping systems, fertilizers, irrigation, tissue analysis, varieties and cultivars
• Education and Training: decision support system, demonstration, extension, farmer to farmer, networking, on-farm/ranch research, participatory research
• Pest Management: chemical control, weather monitoring
• Production Systems: agroecosystems
• Sustainable Communities: local and regional food systems

Idaho wheat production is sensitive to planting-time decisions that affect when wheat reaches heading and grain filling stages, driven by thermal time (i.e., growing degree days, GDD). Delayed planting can push grain filling into late-season heat stress, increasing production risk. Although GDD is familiar to producers and advisors, it is rarely translated into locally validated, variety-specific sowing guidance.

This project proposes to develop GDD-based sowing window guidance for spring wheat in southern Idaho by integrating field experimentation, on-farm trials, and crop modeling. Research Objective 1 will quantify how early, optimal, and delayed sowing dates affect the initiation and duration of grain filling and grain yield for spring wheat cultivars representing contrasting maturity classes at the Parma Research & Extension Center (2027-2028), with validation from two on-farm trials. Research Objective 2 will calibrate and validate the CSM-CERES-Wheat model using the data from Research Objective 1 and regional wheat variety trial data. After calibration, long-term simulations will be conducted using historical weather data across multiple southern Idaho locations and six sowing dates to quantify yield stability and production risk. Sustainability benefits will be quantified using yield variability, probability of low-yielding years below agronomic/economic thresholds, and simulated crop evapotranspiration and irrigation requirements under irrigated scenarios.

Education outputs will include field days, webinars, an Extension bulletin, a decision chart, and dissemination through the Idaho Wheat Commission networks and PNW Pest Alert GDD platform. The project supports sustainable agriculture by improving yield stability and delivering locally validated, practical decision tools for producers.

Research Objective 1: Quantify the effects of sowing dates on spring wheat development and yield in early- and late-maturing varieties

Research Objective 2: Calibrate and validate the CSM-CERES-Wheat model in DSSAT and simulate long-term yield responses to sowing dates to develop variety-specific GDD-based sowing windows for spring wheat

Educational Objective 1: Provide demonstrations and training to stakeholders to increase their understanding of temperature-driven crop development and phenology shifts and production risk associated with sowing dates, and strengthen the adoption of optimized sowing windows

Educational Objective 2: Deliver producer-ready, locally validated sowing date guidance that translates field results and crop model simulations into actionable resources using versatile channels