Effectiveness of organic amendments in enriching nitrogen in compost produced from organic fractions of market waste generated in Dar es Salaam, Tanzania

Abstract

Low nitrogen (N) content remains a key limitation of compost derived from urban organic waste. This study evaluated the effectiveness of selected plant-based organic amendments in enhancing nitrogen content and improving compost quality. Four plant- based organic amendments, Leucaena leucocephala (BN01), Commelina benghalensis (BN02), Morus alba (BN03), and Helianthus annuus (sunflower) cake (BN04), were incorporated into market waste compost at ratios of 1:0.06:0.04, 1:0.06:0.25, and 1:0.06:0.5 (organic waste: sawdust: amendment). Composting was conducted using a 4 × 3 factorial design with three replicates per treatment (n = 36). Temperature, moisture, and pH were monitored throughout the composting period. Total nitrogen, phosphorus, potassium, and organic carbon were analysed using standard laboratory methods. Data were analysed using two-way analysis of variance (two-way ANOVA). Nitrogen content increased significantly with both amendment type (p = 0.0004) and application ratio (p < 0.0001). BN01 recorded the highest nitrogen enrichment (3.5%) at the highest amendment ratio (0.5), compared to 1.1% in the control. No significant interaction between amendment type and ratio was observed (p = 0.11), indicating that the effect of amendment type was consistent across application ratios. Compost pH ranged from neutral to alkaline, with BN01 producing near-neutral compost (pH 7.3), optimal for agricultural use. Leucaena leucocephala proved to be the most effective amendment under the conditions of this study. The findings demonstrate the potential of locally available plant biomass to improve compost quality and support sustainable waste management and agriculture.