Optimizing phosphorus management in canola (Brassica napus L.) through integrated soil, foliar, and fertigation applications under greenhouse conditions

Purpose This study evaluated the effectiveness of foliar spray and fertigation using phosphoric acid combined with soil application of triple superphosphate (TSP) on growth indices, phosphorus uptake, and phosphorus use efficiency in canola grown under low available soil phosphorus. Methods Treatments included different levels of soil-applied TSP as basal fertilization, foliar application of phosphoric acid, and phosphoric acid fertigation. The experiment was conducted in phosphorus-deficient soil (1.6 mg P kg⁻¹) using a factorial arrangement in a completely randomized design with three replications. Results At 0% basal TSP, fertigation increased shoot dry weight by 92% compared to untreated plants, while foliar spray showed no significant effect. With 10% basal application, foliar spray enhanced shoot dry weight by 14% and P uptake by 43%. Moreover, the combination of 50% basal soil application, foliar spray, and fertigation produced results comparable to those of the optimum 100% soil application without fertigation and foliar spray. Under 50% basal TSP application, foliar application of 0.5% phosphoric acid increased agronomic P use efficiency from 90.67 to 99.78 and P recovery efficiency from 23% to 31%. A significant positive correlation (R = 0.735) was found between shoot P concentration at pre-flowering and shoot dry weight. Conclusions The integrated use of phosphoric acid via foliar spray and fertigation successfully met the crop’s phosphorus requirements, allowing a 50% reduction in basal soil phosphorus fertilizer without compromising growth. This approach supports sustainable phosphorus management in canola production.