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

Mahesh Liyanage1, 2, Mohamed M. Hanafi1, 3, 5*, Muhammad Firdaus Sulaiman3, Roslan Ismail3, Gamini Gunaratne2, Saman Dharmakeerthi4, Geethika Rupasinghe5, and Amoda Mayakaduwa5
 
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 effectsof 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 wastebiochar without charging (RBC) were incubated with soil at a rate of 186 mg N kg-1. Incubated soils were analyzedperiodically for soil pH, available NO3--N, NH4+-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. Allamendments showed different N mineralization patterns. Gliricidia, CMP, and TW released N by 94%, 43%, and 24%, respectively. Gliricidiashowed the highest peak of NH4+-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. Gliricidiashowed 0.79 mg d-1 maximum N mineralization rate and 150 mg kg-1 total mineralizable N. The N mineralization wassequenced 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. Inconclusion, GLI meets the immediate plant N requirement, and CBC significantly improves the degraded soil quality.
Keywords: Camellia sinensis, enzyme activities, nitrogen mineralization, organic amendments, soil restoration, tea- growing soil.
1Universiti Putra Malaysia, Institute of Plantation Studies, 43400 Serdang, Selangor, Malaysia.
2Tea Research Institute of Sri Lanka, Soils and Plant Nutrition Division, 22100 Talawakelle, Sri Lanka.
3Universiti Putra Malaysia, Faculty of Agriculture, Department of Land Management, 43400 Serdang, Selangor, Malaysia.
4University of Peradeniya, Faculty of Agriculture, Department of Soil Science, 20400 Peradeniya, Sri Lanka.
5Universiti Putra Malaysia, Institute of Tropical Agriculture and Food Security, 43400 Serdang, Selangor, Malaysia.
*Corresponding author (mmhanafi@upm.edu.my).