Optimizing Nitrogen Supplementation: Timing Strategies to Mitigate Waterlogging Stress in Winter- and Spring-Type Canola.

Canola is an important rotation crop in Australia's high-rainfall zone (HRZ), where frequent waterlogging occurs. Due to its lack of aerenchyma, canola is more vulnerable to waterlogging. Recent studies have shown that nitrogen supplementation can benefit crop growth under waterlogging stress. However, limited reports have addressed the physiological responses and macronutrient changes in either winter or spring canola with strategically timed fertilizer applications. This study investigated the physiological and elemental responses of two canola genotypes to nitrogen application at different timings during waterlogging stress. By imposing waterlogging stress in pot-based trials for 21 days using spring-type (Dynatron) and winter-type (Nizza) canola, our results demonstrated that nitrogen application one week prior to the onset of waterlogging marginally improved soil plant analysis development (SPAD) values in the two types of canola, but only significantly enhanced stomatal conductance along with reduced photosynthetic efficiency in Dynatron at the end of waterlogging, indicating genotypic differences. Furthermore, applying fertilizer a week before waterlogging enhanced macronutrient accumulation in Dynatron, including phosphorus, potassium, magnesium, and calcium. In contrast, Nizza only exhibited a significant increase in magnesium accumulation. Fertilizer application had no effect on reducing Mn and Fe accumulation in canola, indicating that Mn and Fe toxicity, typically associated with soil waterlogging, was not a contributing factor in nitrogen-induced waterlogging alleviation. Collectively, our results demonstrated genotype-specific nutrient dynamics, which should be considered in nitrogen-induced waterlogging alleviation.