Integrated Application of Silicon and Potassium Nitrate Alleviates the Deleterious Effects of Drought Stress on Cantaloupe Plant Growth by Improving Biochemical and Physiological Traits

Cantaloupe (Cucumis melo L.) is a popular, nutritious, and commercially important fruit crop. However, its production at large scale is threatened by multiple challenges in which drought is a major concern. Application of different drought-mitigating essential and beneficial nutrients is one of the important agronomic management options in maintaining productivity under the changing global climate where more severe drought events are projected in the coming future. Individual soil application of silicon (Si) fertilizer (H4SiO4, 20% Si) and seed priming with potassium nitrate (KNO3) has been found highly effective in alleviating drought stress in various crops; however, the combined application of these nutrients in mitigating the negative effects of drought stress has not been thoroughly investigated. The objective of this study was to evaluate the effects of the combined application of Si fertilizer and seed priming with KNO3 on the morphological, physiological, biochemical, and yield responses of cantaloupe under drought stress. A polyhouse experiment comprising of six different combinations of Si fertilizer and KNO3 seed priming (control [without Si and KNO3], 40 kg Si ha(-1), 100 mM KNO3, 40 kg Si ha(-1) + 100 mM KNO3, 200 mM KNO3, and 40 kg Si ha(-1) + 200 mM KNO3) under three soil moisture regimes of 50%, 75%, and 100% field capacity (FC) was conducted. The results revealed a significant negative effect of increasing drought severity on all evaluated parameters where fruit yield, irrigation water productivity, total soluble solids content, and membrane stability index were reduced by 66-77%, 31-46%, 18-31%, and 25-51%, respectively, at 50% FC compared with those at 100% FC across different treatment combinations. The combined application of Si fertilizer and KNO3 seed priming (40 kg Si ha(-1) + 100 mM KNO3) was more effective than the individual application of the two, which resulted in 64-157% increase in root dry matter, 21-78% increase in fruit yield, 20-53% increase in irrigation water productivity, 17-42% increase in total soluble solids content, and 10-59% increase in membrane stability index at the severe soil moisture deficit condition of 50% FC compared with other treatments. However, increasing seed priming dose of KNO3 to 200 mM in combination with 40 kg Si ha(-1) largely remained ineffective as the results with 100 mM KNO3 priming dose along with the same Si fertilizer dose were statistically similar. A combined application of Si at 40 kg ha(-1) (soluble Si) along with seed priming dose of 100 mM KNO3 is recommended for cantaloupe production under severe and moderate drought stress.