As wheat begins to move into the flag leaf (Feekes 9) and boot (Feekes 10) growth stages many growers and consultants are commenting on the short stature of the 2010 wheat crop. We must first address the cause of the short wheat before we can assign yield estimates. Let’s first address planting date. Late-planted wheat will generally be shorter than on-time planted wheat. The yield loss attributed to late-planted wheat is not merely a function of height but reduced tiller number and biomass capacity (planting date impact on wheat yield).
For our on-time planted wheat, development and in this case height is governed by many factors including water, temperature, as well as light quality and quantity. Data from our 2002-2007 winter wheat variety trials show only one year (2005) where there was a positive relationship between yield and plant height (Chart 1.). This suggests that height alone has no direct influence on wheat yield. As long as the minimum threshold for LAI (leaf area index) is reached wheat yield will then be determined by head number, head size, kernel number per spikelet, and kernel size. Since head number, head size, and kernel number per spikelet are already determined we are just waiting on the grain fill period to finalize our 2010 yield.