Winter Wheat Yield Formation as Affected by Water Availability in Colorado.

Winter wheat production in Colorado is mainly limited by water availability. Winter wheat is planted soon after late summer rains, which are unpredictable and may come in early fall or not at all. After winter, the wheat plant experiences water shortage until spring rains come and finally the grain filling period is characterized by drought and heat. Numerical yield components and their relationship with final grain yield can help determining when water shortage is reducing more dramatically yield of winter wheat grown under the above environments. We grew 24 widely grown winter wheat varieties under five different irrigation treatments. Two control treatment, i.e. Dry and Full Irrigation, where the plots were rainfed (soil water content above 30 % to ensure plant survival) and kept above 80 % of soil water content and three treatments, i.e. Jointing, Anthesis and Jointing plus Anthesis, where the plots where kept at 50 % soil water content and additional water was supplied at the developmental stages to bring soil water content up to 80 %. Yield and yield components will be measured at maturity and their relationship will be studied in each treatment to estimate yield formation strategies. The differences in yield formation between treatment will be discussed in the frame of water availability for the crop.