Browsing by Author "Rathnayake, W.M.U.K."

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    Determination of Optimal Grid Size for Mapping Soil Property Distribution for Paddy Cultivation
    (Uva Wellassa University of Sri Lanka, 2016) Dilrukshi, V.P.A.; Rathnayake, R.M.C.W.M.; Rathnayake, W.M.U.K.; Herath, H.M.S.K.
    The importance of understanding spatial variability of soil properties is connected to crop management and planning. This understanding makes it possible to treat soil not as a uniform, but a variable entity to increase the production in paddy cultivation. This study was conducted to propose an optimum grid size for selected soil properties in Bakamuna area in Polonnaruwa district of Sri Lanka. The study area consisted with 6.25 km2 and 96 soil samples were collected within the plough depth of 0-15 cm. The number of samples distribute as 96 samples in 200 m grid size, 37 samples in 400 m grid size, 16 samples in 800 m grid size, 8 samples in 1 km and 2 samples in 2.5 km grid size. The variability of soil pH, electrical conductivity, available P, exchangeable K, available Zn and soil texture were subjected to descriptive analysis and Inverse Distance Weighted interpolation (IDW) technique. Soil pH showed Coefficient of Variation (CV) range from 1 - 7% in different grid sizes, which could be categorized as properties with low variation where CV was less than 10%. Electrical conductivity showed CV range from 30 — 60% in different grid sizes. Exchangeable K range from 10 — 80% and available Zn range from 20 — 60% of CV values indicating medium variability, (CV 10 —100%). Soil available P showed higher CV (>100%) values for 200 m, 400 m and 1 km grid sizes and rest of grid sizes showed medium CV values. Soil texture showed low variability distribution in paddy soil. This study shows the intensity of sampling is related to variability of soil properties. Sandy clay and sandy clay loam soil texture were observed in study area. Sandy clay loam soil texture was found only for two soil samples out of 96 in 200 m grid size. These results indicate 2.5 x 2.5 km grid size is optimum for determine the soil texture. Electrical conductivity and available Zn represent higher spatial variability in 800 x 800 m grid size indicating optimum grid size for mapping of those soil properties. 1 km grid size is optimum grid size for exchangeable K, available P and soil pH. Keywords: Rice, Grid sampling, Soil properties, Coefficient of variation
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    Development of Soil Fertility Map for Paddy Cultivating Areas of Mahaweli System B in Polonnaruwa District
    (Uva Wellassa University of Sri Lanka, 2016) Chathuranga, R.P.G.; Rathnayake, R.M.C.W.M.; Rathnayake, W.M.U.K.; Herath, H.M.S.K.
    Paddy is a major cultivation crop in Polonnarwa District. In recent time a considerable gap has appeared between the potential yield and the real yield. Though several factors contribute to this effect, imbalanced soil fertility is one of the major factors. Therefore, survey of soil fertility was carried out in the area of Mahaweli system B in Polonnaruwa district to identify the status and spatial variability of plant nutrients in paddy cultivating areas to recommend management practices to enhance productivity. Sampling points were identify using 1:50000 topographic maps of Polonnaruwa, Wakaneri, Elahera and Aralaganwila. Geographical Position Systems (GPS) coordinates were used to record the geographic position. Sampling area was divided in to 2.5 x 2.5 km grid sizes and two samples were taken from one grid and 110 samples covering the total land area. In each sampling point, soils were augured up to 15 cm and composited. Soil samples were air dried and analyzed for pH, electrical conductivity, available P and Zn, exchangeable K and Na. The pH value varied from place to place but most of the area covering the irrigation scheme had pH below 5.5. All the area had low EC value (<0.125 dS/m). It indicates the low level of salinity. Soil available P content was considerably lower (<10 ppm) than the recommended value in almost of sampling the area. Available Zn concentration was between 1-5 ppm in all the area while the soil exchangeable Na value was above the recommended value (>100 ppm). There was a low concentration of exchangeable K value (<78 ppm) in most of the area. It is concluded that inverse distant weighted is the most suitable interpolation technique for mapping soil pH, EC, available P, Zn and exchangeable Na and K as regard to the lowest Root Mean Squire Error (RMSE) and Mean Error (ME) values. The soil fertility characteristics of the Mahaweli system B in Polonnaruwa district are not at optimal level to achieve maximum potential of rice yields. Therefore, development and adoption of suitable management practices are needed to enhance and sustain the rice production in this area. Keywords: Soil suitability,Soil fertility, Interpolation, Geographical position system, Mahaweli B