Moody, Georgia2025-01-272025-01-272024https://hdl.handle.net/10182/18005Wheat (Triticum aestivum L.) is a major global crop. It contributes to ~ 20% of global protein intake and is also grown for animal feed. In 2023, 40500 ha of wheat were harvested in New Zealand. It is important to understand the factors that affect crop production to maximize yield. However, the effects of nitrogen (N) on vegetative and early reproductive growth of wheat in high yielding environments is relatively uncharacterized. This experiment quantified light interception, biomass accumulation and partitioning of ‘Kerrin’ autumn feed wheat grown at 0%, 50%, 100% and 150% of the N dose required for a grain yield of 18t/ha in Canterbury, New Zealand. There were two independent experiments, one sown on 20th March 2024 (SD1), and the other sown on 16th April 2024 (SD2). Light interception and ground cover were recorded weekly and biomass harvests occurred every three weeks or at the key Zadok’s stages of 25, 30 and 32, whichever occurred first. Total biomass production for SD1 differed among treatments in the second to last harvest at Z30 stem elongation. The 0% treatment produced 487 kg DM/ha less than the 50, 100 and 150% treatments. The 0% treatment accumulated biomass the slowest at 3.56 kg DM/°Cd. The 100% and 150% treatments showed the highest rate of accumulation at 4.41 kg DM/°Cd whilst the 50% treatment was similar to both the 0% and 100 and 150% treatments. Leaf area index (LAI) for SD1 differed among treatments at the final three harvests. The 150% treatment had the highest LAI of 4.18 at final harvest. 50% and 100% treatments were intermediary with an LAI of 3.97 whilst the 0% treatment had an LAI of 3.5. LAI accumulated at 5.22E⁻⁰³ LAI/°Cd in the 50, 100 and 150% treatments which was faster than the rate of LAI accumulation of 3.87E⁻⁰³ LAI/°Cd in the 0% treatment. SLA differed among treatments at the second to last harvest. 150 and 50% had the highest SLA at 214 cm²/g which was higher than the 0% and 100% treatments at 196 cm²/g. In SD1, the 50% and 150% treatments intercepted a total of 330 MJ PAR/mV at the final harvest. This was higher than the 304 MJ PAR/m² intercepted by the 0% N treatment. The 100% treatments intercepted 324 MJ PAR/m² which was similar to the other treatments. In SD2, there were no differences among treatments for total biomass at each harvest, leaf, stem and dead material at the final harvest or rate of biomass accumulation. The 150% and 0% treatments had a lower proportion of leaf (68%) and higher proportion of dead material (7%) at the final harvest when compared to the 50% and 100% treatments. There were no differences in final LAI, rate of LAI accumulation, SLA, total light interception, or radiation use efficiency (RUE) among treatments in SD2. Differences in biomass accumulation in SD1 were attributed to greater light interception driven by increases in LAI. In SD2, the demand for N was not present during early crop growth which explained no differences among treatments.x, 49 pagesenTriticum aestivm L.nitrogenbiomassdry matterthermal timeleaf area indexlight interceptionradiation use efficiencyspecific leaf areawheatDissertationANZSRC::300407 Crop and pasture nutritionANZSRC::300405 Crop and pasture biomass and bioproductshttp://creativecommons.org/licenses/by-nd/4.0/Attribution-NoDerivatives 4.0 International