Ethephon and Nitrogen Use in Winter Wheat

The plant growth regulator ethephon ([2‐chloroethyl] phosphoric acid) has often been used to reduce height and lodging of intensively managed soft red winter (SRW) wheat [ Triticum aestivum (L.) em. Thell]. The effect of ethephon on traits that determine grain yield has not been widely studied. This study was conducted to determine whether ethephon alters N use and other yield‐related traits in SRW wheat. Nine SRW cultivars were evaluated for 2 yr near Lexington, KY on a Maury silt loam (fine, mixed, mesic Typic Paleudalf). Lodging was negligible in both years. Total plant N at anthesis was significantly increased in plots treated with ethephon at Feekes growth stage (GS) 6 (12%) or GS 9 (15%). Similarly, dry matter (DM) at anthesis was increased 9 and 11% when ethephon was applied at GS 6 and 9, respectively. However, neither total N nor DM at maturity was significantly altered by ethephon application. Remobilization of vegetative N was increased 13% in ethephontreated plots. Ethephon applied at either GS increased the relative importance of N uptake efficiency vs. N partitioning efficiency in determining cultivar variation in N use efficiency. Application of ethephon did not alter grain yield, harvest index, or N harvest index. Ethephon had little or no influence on rate and duration of kernel growth, and slightly decreased kernel size (4%) when applied at GS 6. We conclude that ethephon has a minimal effect on the yield‐determining traits evaluated in this study. However, the pronounced effect of ethephon on the nature of cultivar differences in N use efficiency warrants further study.