Influence of Topographic Parameters on the Yield Variability of the Pelwatte Sugar Plantation in the Moneragala District, Sri Lanka

Abstract

Pelwatte sugar plantation consists of three major cane cultivation areas; Nucleus Estate (NE), settlement scheme and out-growers scheme. It has been reported that the cane harvest has remarkably decreased during past years. The study is aimed to explore the spatial variability of topographic parameters in the NE and to find their impact on the variability of sugarcane yield. Firstly, contour map of the study area was digitised and Digital Elevation Model (DEM) was generated using ordinary kriging with an independent validation. Weighted averages of the yield data were calculated for three consecutiveMaha seasons; 2010/11 Maha, 2011/12 Maha and 2012/13 Mahafollowed by an exploratory data analysis. Topographic parameters; Elevation, Slope, Topographic Wetness Index (TWI) and Topographic Position Index (TPI) were derived from the DEM. Statistical analysis was performed using Rstatistical package. The slope of the terrain ranged from 0-11 in degrees. Most of the terrain area was under 1-3 degree slope category. The curvatures of the cane cultivation area ranged from -11.4 to 11.5 representing three types of terrain features; flat or linear, upwardly concave and upwardly convex. The TPI values, -3.4 to -0.1, 0 and 0.1 to 4.0 showed valley areas, flat areas and the ridge areas of the terrain respectively. Correlation analysis showed low correlations among yield and topographic parameters. The Elevation showed low positive correlations, r = 0.28 and r = 0.21 with yields in 2010/11 and 2012/13 respectively. TPI showed the relatively significant negative correlation,-0.33 with 2011/12 Maha yield.Slope and TWI showed low correlations with yields during each Maha season. It can be concluded that the spatial variability of the topographic parameters of the area is quite significant. The topographic parameters particularly the Elevation and theTPI are relatively significant factors which are affecting on the yield variability of sugarcane in the NE.