Joseph Oakes, Virginia Tech, Warsaw, VA and Ronnie W. Heiniger, 207 Research Station Road, North Carolina State University, Plymouth, NC
The importance of leaf growth in wheat (Triticum aestivum L.) and its effect on grain yield has long been understood. Therefore, an understanding of mainstem leaf growth and development is critical to maximizing potential yield. Field research was conducted on a private farm at Hertford, NC with the cultivar Dyna-Gro “Shirley” to examine the response of winter wheat to starter fertilizer at two different planting dates. Three different starter fertilizers (30% UAN at 30 lb/ac, 11-37-0 at 25 gal/ac, and 9-18-9 at 30 gal/ac) were applied at planting on both planting dates (November 12, 2012 & December 4, 2012). Five plants were randomly chosen from each plot. Each plant was marked and the number of main stem leaves was recorded. Main stem leaves were marked and recorded according to the Haun scale. A leaf’s Haun age is determined by the number of fully expanded leaves plus the ratio of the laminar length of the last visible growing leaf to that of the proceeding leaf. Leaves were marked and recorded at bi-weekly to monthly intervals beginning at emergence and continuing to flag leaf. Grain yield was measured at harvest in order to examine any yield responses. Leaf counts were used to calculate phyllochron interval (PI). The PI is defined as the inverse of the leaf appearance rate, which is determined from the inverse of the slope of the regression of Haun scale growth units against the accumulated growing degree days (GDD).
The PI was shorter in the December planted plots than in the November planted plots (P≤0.05). This indicates that the December planted plots had a faster leaf appearance rate and produced mainstem leaves quicker than the November planted plots. However, there was no significant difference in PI among starter fertilizers applied. Differences in yield closely resembled the differences in PI. Plots planted in December had higher yields than did plots planted in November, which indicates that a shorter PI corresponds to a higher yield. Starter fertilizer resulted in little yield response. However, differences in yield were observed in the December planting date. Plots applied with 9-18-9 at planting had significantly higher yields than did the untreated control and the plots with 30% UAN and 11-37-0.