Consequences of nitrogen mineralization dynamics for soil health restoration of degraded tea-growing soil using organic amendments

Understanding of N mineralization dynamics of frequently available organic amendments in the tea ( Camellia sinensis (L.) O. Kuntze) ecosystem has greater importance in land restoration. Hence, this study focused on assessing the effects of organic amendments on N mineralization and soil quality improvement in tea growing soil. Garden compost (CMP), Gliricidia ( Gliricidia sepium (Jacq.)) leaves (GLI), charged tea waste biochar (CBC), tea waste (TW), and tea waste biochar without charging (RBC) were incubated with soil at a rate of 186 mg N kg -1 . Incubated soils were analyzed periodically for soil pH, available NO 3 - -N, NH 4 + -N, soil P, and S for 120-d. Microbial biomass C (MBC), protease, urease, phosphatase, and dehydrogenase activities were determined at the end of the incubation. All amendments showed different N mineralization patterns. Gliricidia , CMP, and TW released N by 94%, 43%, and 24%, respectively. Gliricidia showed the highest peak of NH 4 + -N after 21-d incubation, depicting rapid ammonification. Charged BC and RBC showed N immobilization throughout the incubation period, which finally amounted to 12% and 17%, respectively. Gliricidia showed 0.79 mg d -1 maximum N mineralization rate and 150 mg kg -1 total mineralizable N. The N mineralization was sequenced as GLI > CMP > TW > CBC > RBC. All amendments showed more than 45% increase in MBC, where Gliricidia gave the highest (146%) compared to the control. Application of CBC promotes all enzyme activities by > 90% over control. In conclusion, GLI meets the immediate plant N requirement, and CBC significantly improves the degraded soil quality.