Utilizing Grain Yield Data from Wheat Demonstration Plots

Wheat (Triticum aestivum L.) cultivar demonstration plots are used widely in Kansas to promote early adoption of high yielding cultivars. These single-replicate plots are often harvested, however, and yields are reported in local newspapers. The objectives of this study were to compare the relative yields of wheat cultivars in demonstration plots and in official winter wheat performance tests and determine the usefulness of demonstration plots as yield indicators. Using cultivar × environment mean square as an error term, significant cuitivar differences could be detected in five of 10 cropping districts, and correlations between demonstration plots and variety performance tests were significant in seven of 10 districts. The five districts with significant cultivar differences and correlations tended to be ones with relatively homogenous soil types. Hybrid wheat cuitivars dominated demonstration plots, but hybrids have not been widely accepted by farmers. Mean yields of demonstration plots over locations can be used as yield indicators, when they represent homogenous environments. R ESULT DEMONSTRATIONS have been a mainstay of the Cooperative Extension Service for educating producers about new farming techniques (Kittrell, 1974). In Kansas, demonstration plots have long been used as a method of introducing farmers to better-adapted cultivars of hard red winter wheat (Triticure aestivum L.). In fact, one county has had wheat demonstration plots on the same farm for 75 yr (R. Seyfert, 1989, personal communication). Demonstration plots can be given credit for the rapid adoption and wide usage of high-yielding cultivars, such as ’Newton’ and ’Arkan’. Each year, approximately 75 of 105 Kansas counties have wheat demonstration plots with field days in the spring. Nafziger (1984) indicated that many counties report yields of unreplicated plots, which may reflect differences in field variability rather than cultivar differences. He suggested that one way to avoid this problem is to explain field variability to farmers and agricultural agents and not to harvest demonstration plots. Unfortunately, considerable pressure is placed on agents by local farmers, seed dealers, and administrative boards not only to harvest the plots but also to report the yields in local newspapers. Also, with the L. Ben-Hui, Dep. of Crop Science (formerly Dep. of Agronomy), Oregon State Univ., Corvallis, OR 97331); J.P. Shroyer, Dep. of Agronomy, Throckmorton, Kansas State Univ., Manhattan, KS 66506; and T.S. Cox, USDA-ARS, Dep. of Agronomy, Throckmorton, Kansas State Univ., Manhattan, KS 66506. Joint contribution of USDA-ARS and Kansas Agric. Exp. Stn. Contribution o. 90-274-J. Received 5 Jan. 1990. *Corresponding author. Published in J. Agron. Educ. 19:164-166 (1990). introduction of wheat cultivars for specific areas of adaptation, there is concern that not enough testing locations are available to evaluate yield performance across environments adequately. Because demonstration plots are numerous and widely dispersed, the temptation exists to use the yield results. The objectives of this study were to evaluate the usefulness of demonstration plots as yield indicators and to compare the ranks of wheat cultivars in county demonstration plots with those in replicated winter wheat performance tests. MATERIALS AND METHODS Data were derived from two sources: county demonstration plots and Kansas Winter Wheat Variety Performance Tests (VPT). Ten publicly released, hard red winter wheat cultivars were furnished to cooperating county agents for use in demonstration plots (Fig. l) during 1983-1986. Agents were encouraged include commercially released cultivars (pure lines and hybrids both public and private) in demonstration plots. Sites were identified by county agricultural agents. Plots were planted and harvested with farm equipment. Plot size varied, but typically was one drill-width wide (3-4.8 m; 10-16 feet) by at least m (100 yards) long. Seeding rates and dates were those typically used by cooperating farmers and varied across the state. Grain yields were reported to the authors in bushels per acre. Yields were averaged within counties each year, so that the basic data unit was for a cultivar-county-year combination. Cultural practices used in the VPT at 16 locations (Fig. 1) were reported by Walter (1986). Two-way analyses of variance for grain yield from dryland demonstration plots and VPT were performed within each of Kansas’ nine crop reporting districts (Fig. 1), utilizing the cultivar × environment mean square for the error term, as recommended by Nafziger (1984). A tenth "district" was defined as comprising all irrigated locations for each data set (VPT and demonstration plots). An environment was a county-year combination for demonstration plots and a locationyear combination for VPT. All irrigated demonstration plots were grouped separately for the analyses of variance. Because the data were highly unbalanced, Type III sums of squares from SAS PROC GLM (SAS Inst., Inc., 1985) were used in the analyses of variance. Least-square means for varieties over all years within districts were computed by PROC GLM. Within-district correlation coefficients between least-square means from demonstration plots and least-square means from VPT (over all years in which demonstration plot yields were available) were computed over all cultivars common to both data sets. 164 J. Agron. Educ., Vol. 19, no. 2, 1990 0 VPT continuously cropped VPT summer fallow ~ VPT irrigated ~ demonstration plots Fig. 1. Kansas cropping districts with wheat variety performance test (VPT) sites and counties with demonstration plots.