Humic acid based liquid organic fertilizer improved the growth of nursery and immature rubber plants grown in Boralu soil series

Humic substances, the major component of soil organic matter, play multiple roles that can greatly benefit plant growth through their indirect or direct effects. Effects of commercially available humic acid based liquid organic fertilizer, Humate Plus® (HP), on growth and nutrient uptake of the rubber plants (Hevea brasiliensis L. Muell. Arg.) during nursery and immature stages were studied. Chemical fertilizers (CF) were applied to rubber plants growing in Boralu soil series (Typic Paleudults) at 0, and 100 % of currently recommended rates. In another treatment 50% of CF was supplemented with HP. Growth of the rubber plants were monitored periodically by measuring plant height, diameter or girth, and in nursery plants dry matter (DM) accumulation as well. Macro nutrient concentrations in the leaves, and different parts of the young budding plants, were determined to assess the nutritional status of the plant. Diameter of the nursery plants that received CF were not statistically different but DM accumulation in shoot was significantly higher, both at cut-back (17%) and 12 weeks after cut-back (13%) in 50% CF+HP treatment compared to those in 100% CF treatment. In field plants, girth at the end of 3rd year was significantly higher (5 to 7%) in 50% CF+HP treatment compared to that in 50% or 100% CF only treatments. Although there was no consistent trend on the effect of HP on leaf nutrient status in young budding plants, total P and Ca uptake at the end of the nursery period was significantly higher in the 50% CF+HP treatment. Results of this study suggest that humic acid based liquid organic fertilizers could be used to cut down the chemical fertilizer usage in rubber plantations while improving the growth of the rubber plants.