Author(s): Zeleke Teshome and Kibebew Kibret
A study was conducted on soil management groups of Metahara Sugar estate in order to characterize them in terms of their physical and hydraulic properties, and develop pedotransfer functions for estimating water contents at field capacity (FC) and permanent wilting point (PWP). Soils of Metahara were classified in to six textural soil management groups (soil classes) on the basis of soil moisture content at pF2 and texture to determine irrigation intervals. These are class 1, 2, 3, 4, 5, and 6 with pF2 moisture contents of <35, 35-45, 45-55, 55-65, 65-75, and >75%, respectively. pF2 is the water content at -10 kPa matric potentials. Ninety eight disturbed and undisturbed samples were taken from surface and subsurface layers. The soil analyses result indicated that mean values of the estate soils varied from class to class and with depth in which bulk density varied from 1.01 to 1.43 g/cm3, particle density from 2.23 to 2.76 g/cm3, total porosity from 40.91 to 61.42%, sand content from 10 to 40%, silt content from 13 to 36%, clay content from 33 to 77%, and organic matter content from 1.18 to 2.69%. The available water holding capacity varied from 99.71 to 212.01 mm/m. The mean saturated hydraulic conductivity varied from 0.96 to 5.95 μm/s while the basic infiltration rate varied from 0.43 to 3.68 cm/hr. The soil water retention characteristic curves (SWRCC) indicate the presence of three distinct groups of soils in the Estate instead of six groups. Water retention at any of the matric potential points considered increased from group 1 (classes 1 and 2) to group 3 (classes 5 and 6). Furthermore, the equation developed using clay content and bulk density as predictor variables was found to be the best equation for predicting gravimetric water content at field capacity and permanent wilting point with reasonable accuracy. Based on the results, the existing irrigation scheduling should be revised for the respective three soil groups.
