Wheat yield response and plant structure following increased nitrogen rates and plant growth regulator applications in Kentucky

To increase wheat (Triticum aestivum L.) yield in Kentucky, many producers are increasing nitrogen (N) rates to 160 or 180 lb N/acre and applying a plant growth regulator (PGR) to reduce plant height and lodging. Replicated field trials were established in three environments (Princeton 2014, Princeton 2015, Lexington 2015) to determine whether increased nitrogen rates and/or PGR applications increase yield or alter the structure of the wheat plant. Five N rates (0, 50, 100, 150, 200 lb N/acre), three cultivars (Pioneer Brand 25R32, Pembroke 2014, Truman), and two PGR treatments (nontreated control, Palisade EC [12.5 oz/acre]) were evaluated. The PGR treatment consistently increased the number of spikelets head-1; however, grain yield was not increased. Plant height was reduced in two environments (Princeton 2014, Lexington 2015) following the PGR treatment. Height reductions were more pronounced in environments with unusually cold winter and early-spring temperatures in which untreated wheat was already significantly shorter than years with less severe winter and spring temperatures. Stem diameter increases were observed when wheat height was not shortened. Grain yield of Pembroke 2014 increased as N rates increased; maximum grain yield for the other two cultivars was achieved at 100 lb N/acre. These results indicate that the PGR did not consistently reduce plant height or increase grain yield.