Evaluation of an NPK 25:7.5:15 fertilizer blend for enhancing tea (Camellia sinensis) yield and nutrient dynamics in Tanzania highlands

Tea (Camellia sinensis) production is closely tied to balanced soil nutrient management, particularly nitrogen (N), phosphorus (P), and potassium (K). This study evaluated the impact of a blended NPK 25:7.5:15 fertilizer on green leaf yield and nutrient dynamics across three Tanzania highland regions Mufindi (Iringa), Lupembe (Njombe), and Rungwe (Mbeya) between 2020 and 2024. Using a randomized complete block design, six fertilizer treatments were tested across five nitrogen rates (0–300 kg N/ha), with NPK 25:5:5 as the reference. Results showed that the blended fertilizer significantly improved soil K? and enhanced P and K uptake in leaves, especially at 60–240 kg N/ha. Higher nitrogen rates offered no additional benefit, indicating diminishing returns. However, increased electrical conductivity and reduced soil pH highlighted potential soil acidification risks. Regional variation in K uptake emphasized the role of local conditions in nutrient response. The findings suggested that balanced fertilization and site-specific strategies to enhance yield.