SOIL RESOURCES OF CHEHA DISTRICT, SOUTH-CENTRAL ETHIOPIA: SURVEY, QUALITY ASSESSMENT AND LAND SUITABILITY EVALUATION

Abstract

The dynamics of land use/cover (LULC) often pose a threat to land resources. Evaluation and understanding of the implications of such changes are indispensable for sustainable land resource management; reinforce the potential of soil functions and optimal use of land resources for effective agricultural productivity. Therefore, the main objective of this study was to investigate the changes of LULC, effects of land use types on soil properties and quality, soil classification and mapping as well as physical land suitability evaluation for major rainfed crops in the Gotam Watershed, Cheha district, South-central Ethiopia. The Landsat imageries for the period of 1973-2017 were acquired and used for the analysis of LULC changes using ArcGIS and ERDAS imagine after complemented with field verification. For soil characterization and classification, a total of nine representative Pedons were opened along a toposequence from three topographic positions (Upper, Middle, and Lower). Soil morphological characteristics of all profiles were described in-situ and soils were classified following the IUSS Working Group WRB soil classification legend. A multivariate statistical technique was used as data reduction technique using principal component analysis (PCA) and developed a minimum data set (MDS) among seven land-use types. Soil quality (SQ) indicators were evaluated and the overall SQ indexing was performed using a weighted method after combining non-linearly transformed indicator scores. All soil samples were collected and analyzed for selected physical, chemical, and biological properties following a standard procedure. A simple limitation method was employed for physical land suitability evaluation for rainfed production of five major crops (teff, maize, bread wheat, potato, and faba bean), and actual and potential suitability maps for each crop were developed using ArcGIS. The results showed that the land area covered by built-up, agriculture, and forest lands, between 1973 - 2017 period increased by 214.71%, 48.36%, and 149.31%, respectively while grazing, shrub, and bare lands decreased by -72.32%, -48.60% and -27.97%, respectively. LULC changes detection matrices revealed that the greater areas of grazing, shrub, and bare lands were transformed into agricultural land, forest land, and built-up areas. The soils of the study area showed variations across topographic positions and within the genetic horizons. The textural class ranged from clay loam to clay with silt to clay ratio of 0.37 to 0.96. The bulk density, total porosity, and available water holding capacity of the soils varied from 1.0 -1.5 g cm-3, 43.92-66.05%, and 103.3 to 157.1 mm/m, respectively. The soil pH was strongly acidic to neutral (4.96 - 7.23). The soils had very low to medium soil OC (0.37-3.28%) and total N (0.03 - 0.24%), very low to low available P (1.05 - 12.11 mg kg-1 ), and moderate to very high CEC (22.24 - 59.00 cmol(+) kg-1 ). The soils of the study area were classified as Chromic Luvisols (Katoclayic, Cutanic), Luvic Rhodic Nitisols, Luvic Nitisols, Eutric Mollic Planosols (Katoclayic), Haplic Vertisols (Hypereutric, Mazic) and Haplic Vertisols (Gleyic, Mollic). The PCA results identified nine soil quality indicators (CEC, total N, OC, pH, silt, sand, available P, Fe, and Mn) with high factor loadings which were retained in the MDS and explained about 83.30% of soil variability among land-use types. The weighted SQ index values ranged between 0.461 to 0.908, while the highest scoring value of 0.998 was recorded for sand and total N. Enset land use had the highest SQ while the lowest was under soils of Eucalyptus plantations. The SQ under all land-use types was negatively xvii affected compared to a natural forest; with a higher degree of SQ degradation under soils of Eucalyptus plantations (- 49.20%), cultivated (-45.72%), and grazing (-45.58%) land uses. The overall suitability evaluation among land mapping units (LMUs) showed that LMU4Bc was actually not suitable (N1c,t, f) for faba bean and marginally suitable (S3t,s,f) for other considered rainfed crops production. LMU2Acl and LMU3Ac were moderately suitable (S2 w,f) for teff and wheat whereas marginally suitable (S3 w,s,f) for maize crop production. LMU1Ac was marginally suitable (S3c,t,w,s,f) for all crops considered. All LMUs except LMU4Bc were identified as potentially suitable land units for all rainfed crop production except faba bean. Yield gap analysis depicted a yield reduction of 53.56 to 60.30% and 42.68 to 48.17% for bread wheat and faba bean crops, respectively compared to their respective potential yield. Therefore, the variations in soil properties as a function of landscape and degraded soil nutrients across land use-types, suggest the need to design appropriate land management options for sustainable use of soil resources at their optimal functioning, thereby improving soil quality and agricultural productivity in the watershed