The agricultural sector is considered as a major driving force of Sri Lankan economy and it contributes about 7.5 % to the national GDP, while providing over 30 % of employment opportunities (Central Bank of Sri Lanka, 2017). Paddy yield levels have not been increasing significantly over the last two decades and the country’s average yield was lowering while the potential is being far higher (Census and Statistics Department 2015). Paddy (Oryza sativa L), a semi aquatic cereal, has been originated in the northern region of India. There are three main types of rice cultivars namely Indica, Japonica and Javanica (Datta 1981). Rice is the staple food in Sri Lanka and majority of the world. Almost three billion people in Asia, Africa, and Latin America rely on rice for their main meals (Datta 1981).
Increasing salt concentration in the soil solution, commonly known as salinity is becoming an important stress factor causing significant reduction in the productivity of agricultural crops, both globally (Munns & Tester, 2008) and in Sri Lanka (Sirisena & Herath, 2009). In agriculture, a soil having a salt concentration exceeding an electrical conductivity (EC) value of 4 dS m-1 is classified as saline. The sensitivity to salinity varies in different crop species while rice is classified as one of the most sensitive crops (Munns & Tester, 2008).
Measuring salinity in irrigation water is possible with an Electromagnetic Conductivity Meter. It measures the concentration of charged particles in a water sample and reports it in units of salinity (dS m-1). GIS (Geographic Information System) has been known as a powerful tool to analyze spatial data and this technology is recently applied to agricultural sector in Sri Lanka as well. This research aims on application of GIS by mapping the status of salinity of paddy fields in Kamburupitiya DS Division to identify the most salinized areas and apply a site specific management system (Kahandageet al., 2016).
High concentrations of salts in irrigation water, (Ghassemi et al., 1995), rising sea level due to global warming (IPCC, 2007) and high evapotranspiration rates (De Costa, 2009) are some of the factors which contribute significantly on salinity of paddy cultivation. Out of 60 million ha of rice grown worldwide, nearly 80 million ha are grown under irrigation (IRRI, 2011). Seventy five percent of the 720,000 ha of rice in Sri Lanka is cultivated under irrigation (IRRI, 2010). Irrigated lands have higher productivity in comparison to rainfed lands. The effect of increasing salinity levels in irrigated rice lands on total rice production, will therefore be proportionately greater.
In Kamburupitiya area, the extent under rainfed and major irrigated paddy is more or less equal, while paddy irrigated with minor irrigation systems is about 1,360 acres (24%).It is reported that paddy field of Kamburupitiya area is affected by salinity of irrigated water. Therefore it is very important to identify the areas of salinization and the degree of salinization of affected areas of Kamburupitiya DS division.
The objectives of the study are to; • Identify salinity levels of the irrigation water in paddy fields in Kamburupitiya areaboth Yala and Maha seasons • Map salinity levels of irrigated water supply to paddy growing fields using GPS/GIS techniques
Kamburupitiya DS division belongs to Matara district located in the Southern province. Kamburupitiya DS Division represents approximately 68 km2 of land area which comprised of 39 Grama Niladhari (GN) Divisions. The area falls within 6.0779° N, 80.5633° E. According to Kahandage et al., 2016,the 80% of GN Divisions in Kamburupitiya are observed lower paddy yield compared to the national average value of 4.25 mt/ha.
Paddy fields in Kamburpitiya DS division will be selected as the sampling frame. Anicuts which supply irrigation water to paddy field were selected as specific sampling points where water samples were collected to measure pH, EC, salinity and TDS values. Water samples were collected from the all anicutes located in 46 Grama Niladhari divisions in Kamburupitiya DS division.
Water samples to measure EC, will be collected from the anicut systems attached to the paddy fields. Portable EC meter will be used to measure salinity in each sample. GPS points in each sample points will be recorded at the time of sample collection.
A pre testing process will be carried out by selecting several paddy fields in the area. Depending on the pre testing results, the data collection and processing will be modified.
Salinity map will be developed using the EC meter readings and the GPS points using ArcGIS software.