Effect of Potassium Humate, Phosphorus and Copper on Onion Quantitative and Qualitative Yield

Previous research has been limited regarding the combined impacts of copper and potassium humate under various phosphorus fertilization levels on onion crops. So, a field trials were performed during two successive winter seasons of 2021 - 2022 and 2022 - 2023 aiming to evaluate three levels of calcium superphosphate (representing 100 %, 75 % and 50 % of the phosphorus recommended dose) as main plot treatments, along with three levels of potassium humate soil addition ( 0.0 %, 1.0 % and 2.0 % ) as sub-plot treatments. Additionally, foliar spraying of copper was carried out at three different rates (0.0 %, 0.1 % and 0.2 %) as sub-subplot treatments. These factors were examined individually or in combination to assess their impact on onion performance, quantitative yield, and qualitative attributes. Firstly, in terms of the individual effect of phosphorus recommended dose (PRD), the application of 100% of PRD demonstrated superior impacts on onion growth performance, quantitative and qualitative yield compared to 75% and 50% of PRD, respectively. Secondly, focusing on the individual effect of soil addition of potassium humate, all parameters related to growth performance, quantitative and qualitative yield, such as bulb weight and diameter, neck diameter, marketable bulb yield, total dissolved solids (TDS), total sugar (%), carbohydrates, and crude protein, exhibited an increase with higher rates of added potassium humate. Thirdly, the values of all parameters studied increased as the rate of copper application increased, indicating a positive correlation between copper application and onion crop performance. Lastly, the combined treatment of 100% of PRD with 2.0% potassium humate and 0.2% copper recorded the highest values across all measured parameters. Additionally, the combined treatment of 75% of PRD with potassium humate at rates of 1.0% or 2.0%, along with copper at rates of 0.1% and 0.2%, outperformed the individual application of 100% PRD in terms of the measured parameters. Therefore, it can be concluded that the combined addition of potassium humate (as soil addition) and Cu (as foliar application) has a vital role in improving the quantitative and qualitative yield of the as well as raising the efficiency of phosphate fertilizers.