Wheat Yield Response and Plant Structure Following Increased Nitrogen Rates and Plant Growth Regulator Applications in Kentucky

Abstract

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.

Plant Growth Regulator and Nitrogen Applications for Improving Wheat Production in Michigan

“…Increased wheat grain yield following PGR application was also reported by Matysiak (2006) and Penckowski et al (2009). In contrast, Rajala and Peltonen‐Sainio (2002), Wiersma et al (2011), and Knott et al (2016) did not observe increased grain yield following PGR applications. In the present study, PGR increased yield even when lodging was minimal or nonexistent perhaps due to physiological changes within the plant as increased tiller density following PGR application has been reported in multiple wheat cultivars and cool‐season turfgrasses (Ervin and Koski, 2001; Hafner, 2001; Rajala and Peltonen‐Sainio, 2001).…”

“…Data on other wheat physiological responses to PGR are limited. Knott et al (2016) reported increased spikelets head −1 following PGR application. Little information regarding the effect of PGR rate or application timing in wheat is available.…”

“…Multiple researchers have reported decreased height and decreased lodging following PGR application to wheat (Matysiak, 2006; Nolte, 2007; Penckowski et al, 2009; Wiersma et al, 2011; Knott et al, 2016). Decreased lodging was attributed to increased stalk strength, as well as decreased plant height (Matysiak, 2006).…”

“…Decreased lodging was attributed to increased stalk strength, as well as decreased plant height (Matysiak, 2006). Increased stem diameter was observed and may contribute to enhanced straw strength (Zagonel et al, 2002; Knott et al, 2016). Data on other wheat physiological responses to PGR are limited.…”

“…A trend of increasing N rates and using a PGR to combat lodging has now emerged. Limited research on PGR and N rates is available, but Knott et al (2016) reported no difference in wheat height or peduncle diameter among recommended (100 lb N/ac) and elevated (150 and 200 lb N/ac) rates in Kentucky following PGR application. The objective of this study was to investigate the individual and combined effects of PGR application and N rate on wheat growth, grain yield, plant structure, and lodging incidence.…”