Dr Rakesh Awale1, Dr Michael Bell1, Dr Timothy McLaren2
1The University of Queensland, Gatton Campus, Gatton, Australia, 2The University of Queensland, St. Lucia Campus, St. Lucia, Australia
Biography:
Dr Awale is a post doctoral research fellow at the University of Queensland Gatton Campus since 2023, with research focus on nutrient (N and P) cycling and management in grain and cotton crop production using organic and chemical amendments.
Abstract:
Understanding crop nitrogen (N) requirement is essential for devising optimum N fertilisation need to maximise yield. A two-year study to evaluate whether cotton N requirements vary with crop yield potentials was conducted in southeast Queensland. In 2022/23, eight urea-N rates (0 to 350 kg/ha) were applied to five treatments, which aimed to use source-sink manipulation to change crop yield potential for a single cotton variety: (i) standard crop management targeting optimum yield (standard) with all N applied prior to sowing (upfront-N), (ii) restricted canopy expansion (extra growth regulant) with upfront-N, (ii) standard canopy management with pulsed periods of 30% radiation reduction (shaded) during fruiting, with upfront-N, (iv) standard crop management with N application split between pre-planting and flowering (split-N), and (v) extra growth regulant with split-N. In all treatments, cotton responded significantly to N application with Mitscherlich response functions describing the relationships between lint yield and N rate. The 90% maximum lint yield (Y90) was lower in shading/upfront-N (2540 kg lint/ha) compared with standard/upfront-N, standard/split-N and restricted canopy/split-N (2870–2980 kg lint/ha). Crop N uptake at Y90 varied significantly (170–230 kg N/ha) and was linearly related to Y90 (R2=0.59) across treatments. Despite similar biomass N accumulation to high-yielding treatments, lower seed yield in shading/upfront-N resulted in lower seed N removal. Optimum N fertiliser rates at Y90 varied considerably (100–230 kg N/ha), but optimum rate was not correlated to Y90. Cotton N requirement was largely driven by yield potential, but inefficient crop internal N utilisation could also elevate N demand in low-yielding crops.