Foliar nutrient content and decomposition of green manure species viz. Gmelina arborea Roxb. and mallotus philippensis (Lam.) Muell. Arg.

Abstract

A detailed work was undertaken in the College of Forestry, Kerala Agricultural University, Vellanikkara, Thrissur, Kerala during 2011 - 2014 to study the foliar nutrient content and the decomposition rate of the leaf biomass of two green manure tree species, i.e. Gmelina arborea and Mallotus philippensis, as affected by seasons and field conditions. The experiment was conducted in an open and home garden during the wet season and the dry season. The rate of decomposition was generally faster for both the species studied under all the study situations. However, Gmelina arborea showed faster rates of leaf biomass decomposition than Mallotus philippensis. With respect to seasons, wet season reported faster decomposition for both the tree species. Although no significant influence of field conditions on the decomposition rate was observed, open area registered faster decomposition than homegarden. Decay coefficient recorded was maximum for Gmelina arborea. Generally, both the species under all the conditions followed a biphasic pattern of biomass decomposition. The initial nitrogen content, C: N ratio, lignin content and lignin: nitrogen ratio of the leaf biomass influenced the decomposition rate. The decomposition rate was also found to be a function of soil moisture content and soil temperature. Leaf biomass of Gmelina arborea showed rapid release of nutrients than Mallotus philippensis. Among the nutrients, potassium registered faster mineralization followed by nitrogen for both the species under all the study situations. The lowest mineralization tendency was seen for phosphorus in both the species under all the conditions. Also, significant improvement in the soil nutrient status of the soil was observed by the incorporation of leaf biomass of Gmelina arborea and Mallotus philippensis into the soil. However, no significant differences were observed with regards to the species on increasing the soil carbon and nitrogen content. The leaf biomass of Gmelina arborea showed maximum improvement of soil phosphorus content and exchangeable potassium.