Verification of Variable-rate Nitrogen Fertilization Using Tiller Number as a Diagnostic Reference in Wheat Cultivar ‘Sanukinoyume 2009’

Abstract

Variable-rate nitrogen (N) application effectively stabilizes high wheat yields, but few studies have examined the effects of the timing and amount on N application on the yield and spike number. In this study, we tested whether variable-rate N application at the emergence (GS11) and/or fourth leaf appearing stage (GS14) would enhance stem number, ear number and yield in a canopy. In the plots with only half the standard number of seeds sown (half-sown), the number of stems in GS11 was about half of that in the standard plot. The maximum number of tillers in the half-sown plots was similar irrespective of N application at GS11. In the 2021/22 season, the number of maximum tillers was about 350 m^-2 irrespective of the N applied at GS14. The reason for the lack of increase in the number of tillers was that the increase of N content at the initiation of the stem elongation stage (GS30) was less than 6% of the applied N. Yield in 2021/22 was 445 g m^-2, similar to the standard sowing plot, irrespective of N application at GS11 and/or GS14. Yield in 2022/23 was 38 to 48 g m^-2, and was significantly lower with increasing N application at GS11. The effect of N application on N content at maturity was similar to that on yield. Plots, where N was applied at GS11 and/or GS14, showed higher canopy coverage at GS30 and a severe lodging degree at maturity. When applying greater amounts of N after GS30, it was considered more important to establish a reliable number of wheat plants than with variable-rate N application at GS11 and/or GS14.