Browsing by Author "Ratnayake, R.R."

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Soil carbon sequestration capacity in paddy soils of Kurunegala district, Sri Lanka with respect to its agro climatic regions
(Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Lakmali, H.K.M.; Paranavithana, T.M.; Perera, G.A.D.; Ratnayake, R.R.
Paddy field ecosystems are considered as one of the major carbon pools as they store a significant amount of carbon under water-logged conditions. Hence, it is essential to understand the carbon storage capacity in paddy fields as this would help to identify the processes related to soil carbon sequestration potential in such ecosystems. However, the soil carbon content may vary with the prevailing climatic conditions of the site. Kurunegala is one of the districts in Sri Lanka with heavy paddy cultivation and also it experiences three different agro climatic conditions (Dry, Intermediate and Wet). This study aims to assess, how the soil carbon sequestration capacity in paddy soils would vary concerning three different agro climatic conditions in Kurunegala district. Adopting the conditional Latin hypercube sampling (cLHS) design, 200 soil samples were collected from two depths, surface soil layer (0 – 15 cm) and sub-surface soil layer (15 – 30 cm) so as to represent the agro climatic regions. Soil Moisture Content (MC), Soil pH and Electrical Conductivity (EC), Bulk Density (BD), Total Carbon (TC), Microbial Biomass Carbon (MBC), Labile Carbon (LC), Water-Soluble Carbon (WSC), Total Nitrogen (TN) were analyzed using standard protocols. Results showed that the total C and MBC contents were higher in the paddy soils collected from the wet zone climatic region and low soil pH (5.5-6.5) and anaerobic conditions prevailed could be contributing to this situation. Further, the Soil C stock (70.54 Mg ha-1) was higher in the wet zone climatic region compared to dry and intermediate climates. Increased TC content in paddy soils will cause to increase in the soil TN content too. Available P and NO3 - contents in the paddy soil were higher in the Intermediate zone but the pH and the EC were higher in the soils from the dry zone. In conclusion, the paddy soils under the wet zone climatic conditions showed a higher carbon stock and a high potential to retain soil carbon than those in the other two agro climatic regions.
Soil nutrient availability in different vegetation types of Kunckles conservation forest in Sri Lanka.
(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Rajapaksha, R.P.S.K.; Madawala, H.M.S.P.; Gunathilake, S.K.; Ratnayake, R.R.
Estimates of soil nutrient availability in tropical land use types are critically important to understand the function of soil in the global nutrient cycles and the sustainable management of tropical ecosystems. The aim of this study was to quantify and compare the macro and micro nutrient availability in soils in different vegetation types in the Knuckles Conservation Forest (KCF) of Sri Lanka. Soil samples were collected within two depth layers (0-15 and 15-30 cm) considering the proportion and the accessibility to each vegetation type. The selected vegetation types were montane forest (MF), sub-montane forest (SMF), moist monsoon forest (MMF), open and sparse forest (OSF), grassland (GL) and forest plantation (FP). The macro nutrient (N, P, K, Ca and Mg) and micro nutrient (Fe, Mn, Cu and Zn) availabilities were analyzed for two soil depth layers (0-15 and 15-30 cm). A total of 1224 samples were collected from two depths and pooled to form 408 composite samples. General Linear Model in Analysis of Variance was performed using Minitab 16 to analyze the data. Availability of N and P in KCF soils ranged between 8.18 - 19.76 mg/kg and 0.21 - 0.45 mg/kg, respectively among the vegetation types in the 0-15 cm layer. N and P availability was significantly higher in SMF (21.23 and 0.49 mg/kg respectively) and OSF (22.08 and 0.47 mg/kg) soils compared to other vegetation types. Significantly low N availability was observed in both GL (5.07 mg/kg) and MF (7.32 mg/kg) soils. It was also found that P was significantly deficient in MF soils compared to other vegetation types in KCF. Vegetation types in KCF showed significant differences in the availability of K, Ca, Mg, Fe, Mn, Cu and Zn in soils. Fe availability in soils varied between 187.4 - 682.3 mg/kg while Mn varied from 28.52 - 85.26 mg/kg. Results concluded that spatial availability of nutrients such as N and P in mineral soil may be decreased in MF comparing to the other vegetation types due to the environmental conditions such as acidic soil pH, low temperature and microbial growth existing at high altitudes of KCF. This suggests limitation of plant growth in MF by deficiency of one or several nutrients at higher altitudes. Availability of K and Ca in KCF may be affected by parent material exposed on to the soil surface. This baseline information will address the dearth of data on soil nutrient availability of different ecosystems in the tropics, hence useful in future conservation purposes of the tropical forest ecosystems.