ORGANIC COMPOSITE MANURE: A SUSTAINABLE APPROACH TO IMPROVE SOIL HEALTH AND YIELD IN MATURE TEA

Assessment of soil fertility and microbial activity is crucial for preserving soil health and ensuring sustained tea production. This study evaluates the impact of newly developed organic resource-based composite manure, applied through broadcasting methods, on tea yield and soil health, as well as reducing reliance on inorganic fertilizers. The research was conducted at BTRI Farm between 2022 and 2023, using eight treatments and three replications. Harvesting data was collected at weekly interval throughout the plucking season. Treatment T8, which combined 2.0 t/ha of composite manure with 40% of the recommended chemical fertilizer dose, resulted in the highest yield (2550 kg/ha), a 26.70% increase compared to the control. Although T8 produced the highest tea yield, the partial economic analysis showed that the most economically viable treatment for mature tea was T6, which combined 1.5 t/ha of composite manure with 60% of the recommended chemical fertilizer dose, achieving the highest Marginal Rate of Return (21.16%). Higher doses of composite manure paired with reduced chemical fertilizer rates significantly improved tea yield (ANOVAF = 63.348, p < 0.05). Regardless of treatment, soil chemical parameters and microbial activity increased compared to the control. The highest microbial activity (0.58±0.02 mg CO2/g) was observed in T8. Treatment T8 also showed the greatest increase in soil pH (5.53±0.23), organic carbon (1.45%±0.04), total nitrogen (0.130%±0.002), available phosphorous (174.52±2.1 mg/kg), and available potassium (75.97±5.2 mg/kg). Meanwhile, the highest available calcium (400.76±2.2 mg/kg) and available magnesium (103.86±1.6 mg/kg) were found in T3 and T5-treated plots, respectively. These changes represent significant improvements over the initial soil conditions, and the organic composite manure can enhance not only the soil properties but also increase the yield of mature tea. Therefore, it can be summarized that the most effective dose of composite manure is 1.5 t/ha, which can reduce 60% of the use of chemical fertilizers.