Excessive nitrate in groundwater, caused by fertilizer overuse and poor wastewater management, poses a significant threat to its quality and long-term sustainability. Zeolite, a low-cost mineral, has positive effects on agricultural soil, plant growth, and groundwater. This study evaluated ammonium-clinoptilolite zeolite as a slow-release nitrogen fertilizer for agriculture. The clinoptilolite zeolite (NCC) was prepared in chip (NH₄-ICC) and powder (NH₄-ICP) forms using an impregnation method and microwave reactor treatment (NH₄-ECC). The additional treatment was used as the control (T4) using just natural zeolite as the growing substrate. The zeolite-clinoptilolite/natural zeolite ratio levels for treatments T1, T2, and T3 were 5, 15, and 25%, respectively in terms of volume. The effectiveness of these zeolites in promoting the germination and growth of bell pepper seedlings (Capsicum annuum L.) was assessed under greenhouse conditions for 23 days. The data were analyzed with the statistical software R v4.2. The experiment had a completely randomized design based on the combination of two factors: the type of zeolite and the level of zeolite-clinoptilolite/natural zeolite proportion. All the treatments were irrigated using just water without any fertilizer. Several parameters were analyzed, including plant growth, root length, chlorophyll, leaf number, and dried plant weight. The results showed significantly higher plant growth, leaf number, and dried plant weight. T1C, T1P, and T2P had high leaf area. There was no statistically significant difference in chlorophyll. However, there was a trend towards increased stem thickness, plant height, and dried plant weight compared to the control. This research highlights the important potential of zeolites as a component of ammonium-based fertilizers. Their ability to minimize nutrient loss and control release makes them a valuable tool for sustainable agriculture.