The impact of fertilizing <i>Swietenia mahagoni</i> (L.) Jacq. seedlings under water stress with various nitrogen and phosphorous sources

Background: Drought represents a significant global threat, affecting agricultural productivity and leading to water shortages. Nitrogen (N) and phosphorus (P) are essential macronutrients that promote plant growth and enhance tolerance to drought. Swietenia mahagoni (L.) Jacq. (mahogany), is a high-quality timber species recognized for its extensive commercial and pharmaceutical applications. The present study aims to study the effect of fertilization by different forms of N and P on the growth and drought tolerance of mahogany seedlings. Results: The application of three levels of soil water regime (100%, 75%, and 50%, field capacity [FC]) on mahogany seedlings, with different combinations of N fertilizers (ammonium sulfate [AS], ammonium nitrate [AN], and urea [UR]) and P (phosphoric acid [PA], superphosphate [SP], and triple superphosphate [TS]) in two seasons, indicating that the water regimes and all the combinations of N and P forms significantly increased mahogany growth (number of leaves, root length, stem height, the fresh and dry weights of shoots, roots, stem, and leaves), water use efficiency (WUE), and N and P leaves content. The highest values were obtained from irrigation with 100% FC, while the lowest was from 50% FC. All combinations of N and P significantly enhance all growth parameters compared to the control. Furthermore, AS, PA, and AS-PA had significantly the highest values of all studied characteristics. While AN, SP, and AN-TS had the lowest values. The interaction between different water regimes and different N and P combinations had a highly significant (p ≤ 0.001) effect on WUE, root length, leaves dry weight, and N leaf content in both growing seasons. While fresh and dry weights of stem and shoots were significant at p ≤ 0.05 in the second growing season. Conclusions: Drought stress had a negative impact on all vegetative characteristics, WUE, and N and P leaves content of mahogany seedlings. All the combinations of N and P significantly improved growth characteristics under drought conditions, but the most effective treatments were AS, PA, and AS-TS. The present study is very important in that it provides critical insights for enhancing drought adaptation, reducing water usage, and enhancing plant growth characteristics.