Comparative Assessment of Treated Wastewater and Freshwater Irrigation on Chlorophyll Content, Growth Performance, and Soil-Water Quality of Tomato (Solanum lycopersicum) and Periwinkle (Catharanthus roseus) in Muscat, Oman

Abstract

The arid conditions of Oman and the ongoing depletion of groundwater have increased focus on treated wastewater (TWW) as an alternative irrigation source. This experiment involved comparing physiological, growth, soil, and water-quality of tomato (Solanum lycopersicum ), a fruiting crop, and Madagascar periwinkle (Catharanthus roseus), a non-fruiting ornamental plant under TWW or freshwater (FW) irrigation. The controlled pot experiment in Muscat, Oman, took place between December 2025 and March 2026, and lasted four months. Plant growth (height), SPAD chlorophyll, reproductive biomass, soil pH, soil macronutrients (N, P, K) and TWW quality were checked. Statistical analysis with descriptive statistics, percentage difference, t-tests, one way ANOVA, and Pearson correlation analysis were utilized. The findings showed that Tomato-TWW possessed a statistically significant final SPAD value, which was 28.7 percentage points higher than Tomato-FW, and statistically significant general treatment group differences existed (F = 6.776, p = 0.0018). It is important to note that only Tomato-TWW yielded fruit (87 g yield) whereas Tomato-FW did not yield fruits. Periwinkle exhibited no significant or overall changes in chlorophyll and equal counts of flowers across treatments. The Periwinkle-TWW soil contained 136.7% more nitrogen than Periwinkle-FW, which is indicative of species-specific nutrient processes. One of the most important revelations was the dropping pH of TWW of 5.88 to 4.53, which is lower than the recommended pH of FAO of 6.5 to 8.4. Electrical conductivity (1519 to 1658 mu S/cm) and total dissolved solids (759-819 ppm) were moderately high and stable. The study demonstrates that TWW irrigation enhances chlorophyll content and reproductive output in fruiting crops while raising concerns about water quality management.