Stand-alone and combined effects of protein hydrolysate and humic-like substances derived from waste materials on the growth, physiology and mineral nutrition of tea nursery plants by Raguraj, Sriharan, Kasim, Susilawati, Sanali, Bellana Vithanage Roshika, Senarathne, Thakshala Thilini Kumari, Weerathunga, Saman Kumara, Damayanthi, Maha Makkalage Nalika, Wijesinghe, Senarath Pathiranalage Shyamali Kumari, Amali, Rathnasekara Kuruppu Arachchige, Madushani, Maha Gamage Kusala, Liyanage, Liyana Rallage Mahesh Chaminda