Soil nitrogen and tea leaf properties in organic and conventional farming systems under humid sub-tropical conditions Sangeeta Das & Prodeep Kumar Borua & Rajib Mohan Bhagat Received: 26 June 2014 /Accepted: 26 March 2015 # Springer Science+Business Media Dordrecht 2015 Abstract The effects of organic (OFS) and convention- al (CFS) farming systems on soil nitrogen and tea (Camellia sinensis L.) leaf physiological as well as biochemical properties under humid sub-tropical condi- tions were studied at the experimental field of Tocklai Tea Research Institute, Jorhat, Assam, India. A part of the field under CFS was converted to organic in 2008 by using different organic manures, viz., vermicompost, P- enriched vermicompost, de-oiled neem cake, and inserting green crop, besides phosphorous (P) and po- tassium (K) solubilizing bacteria. After 4 years of con- version process, OFS resulted in significantly higher values for leaf total catechin (262.03 mg g -1 ), (-)-epi- gallocatechin gallate (EGCG, 159.97 mg g -1 ), and (-)- epicatechin gallate (ECG, 42.93 mg g -1 ) contents al- though there was up to 22 % reduction in tea yield. On the other hand, CFS resulted in significantly higher values for soil available nitrogen (154 mg kg -1 ) contents as well as for leaf chlorophyll a (2.51 mg kg -1 ), chlo- rophyll b (1.02 mg kg -1 ), and total chlorophyll (3.53 mg kg -1 ), contents. No significant difference was observed for caffeine, (-)-epigallocatechin (EGC), (+)-catechin (C), and (-)-epicatechin (EC) contents be- tween the two farming systems studied. Correlation analysis indicated that (-)-EGCG was the major cate- chin fraction significantly correlated with leaf chloro- phyll a, chlorophyll b, and total chlorophyll contents. The present study has provided knowledge on soil available nitrogen as well as leaf physiological and biochemical contents in tea shoots under humid sub- tropical conditions in Northeast India. Keywords Nitrogen . Organic farming . Conventional farming . Leaf properties Introduction Tea (Camellia sinensis L.) is a plantation crop grown commercially for its young harvestable leaf. Tea is cul- tivated in 563.98 thousand ha with an annual production of 1208.78 million kg (Tea statistics annual report 2014) in the humid sub-tropical climate of India, more partic- ularly Northeast (NE) India. To replenish the high nu- trient removal (>60 kg N ha - 1 year - 1 and >30 kg K ha -1 year -1 ; Sitinei et al. 2013), following the transition from conventional to organic and low- input farming, organic manures have to be applied peri- odically. Organic farming system (OFS) is considered to be more sustainable than chemical-based agricultural systems (Avery 2007). Currently, organic produce gen- erally commands a higher price than conventional pro- duce (Oberholtzer et al. 2005), prompting producers to grow crops organically. In tea ecosystem, organically Org. Agr. DOI 10.1007/s13165-015-0116-4 S. Das (*) : R. M. Bhagat Soils Department, Tocklai Tea Research Institute, Tea Research Association, Jorhat 785001 Assam, India e-mail: sangeeta.ranidas@gmail.com R. M. Bhagat e-mail: rajivmbhagat@gmail.com P. K. Borua Department of Life Sciences, Dibrugarh University, Dibrugarh 786004 Assam, India e-mail: boruapk032@rediffmail.com