Roles of Leucaena leucocephala (Lam.) on Sandy Loam Soil pH, Organic Matter, Bulk Density, Water-Holding Capacity and Carbon Stock Under Humid Lowland Tropical Climatic Conditions

Leucaena (Leucaena leucocephala Lam.) trees planted in alley cropping or established
on fallowed farms by natural means contribute significantly to soil health and productivity by
influencing various soil properties. In this study, the effects of L. leucocephala (Lam.) on
sandy loam soil pH, organic matter content, bulk density, water-holding capacity and carbon
stock were investigated under humid lowland tropical climatic conditions in Papua New
Guinea (PNG). Soil samples were collected from 60 cm deep piths dug out from 1 m and 2 m
away from the base of the legume trees. The control soil samples were collected from
adjacent grassland dominated by Imperata cylindrica (L.), 10 m away from the legume trees.
In all the piths, soil samples were collected from the 0-20, 20-40 and 40-60 cm profiles. The
results showed presence of the legume trees acidifies the soil (lowers pH), lowers surface soil
organic carbon, improves the water holding capacity within the surface soils and helps
improve bulk density, ideal for root growth. Comparatively there was more carbon in the
surface soil of the grassland than under the legume trees. In most tropical regions, grasslands
are often set a blaze for various land uses and the high carbon content is a potent source of
CO₂ emission, contributing to the greenhouse gases (GHG) in the atmosphere. The low
carbon stock measured under the legume trees means reduced emission of CO₂ when burnt
and more benefits for the sandy loam soil. This study has implication for management of
sandy loam soil using L. leucocephala (Lam.) under humid lowland tropical climatic soil
conditions.