Abstract:
Sub-montane forests in the Knuckles conservation region in Sri Lanka had been
cleared for cash crop cultivation during the colonial era. Those lands were
abandoned due to low yield and subsequently, they developed into barren
grasslands. Previous research found that the grassland soils had a lower nutrient
content than the neighbouring forest soil. In the present study, we tested the
hypothesis that the establishment of native tree islands with the presence of
Gliricidia sepium as a shade plant, and with the application of Biofilmed
Biofertilizer (BFBF) positively affects the soil nutrients status of the degraded
land through soil restoration processes. The research design consisted of four
blocks and each block consisted of two sets of an experimental plot with three
different sizes of the island (2 m2, 4 m2, 8 m2). Inside the islands, four native plants
(Macaranga indica, Bhesa ceylanica, Symplocos cochinchinensis, and Eugenia
bracteata) were randomly established under four treatments [(+G+B), (-G+B),
(+G-B) and (-G-B)], with and without G. sepium (+G and -G) as shade plant and
with and without the application of BFBF (+B and -B). Soil Organic Carbon
(SOC), Ammonium, Nitrate, Phosphate, and Cation Exchange Capacity (CEC)
were determined in soil collected from islands of different sizes and the nearby
grassland at the initiation of the field experiment as well as after two years. The
treatment +G+B in the large island (8 m2) showed significantly higher (p<0.05)
SOC, and ammonium than that of the initial soil samples and the grassland soil.
Nitrogen, CEC, and phosphate levels were significantly (p<0.05) higher in the
larger islands than in other island sizes. Higher Relative Growth Rates (RGRh)
and the survival of native plants were observed in the large islands.
Microorganisms in the BFBF-treated islands helped to accelerate the
decomposition of organic matter and release nutrients that soil receives from the
native plants and G. sepium. The presence of G. sepium as a nurse plant and the
application of BFBF (G+B+) improved soil nutrients in the large islands
compared to medium and small islands.
