Abstract

The long term use of heavy weighted agricultural tractors for sugarcane cultivation has caused long lasting soil physical and hydraulic properties altering. However, information on the extent of change is scant. In this context, a study was conducted in 2017 at Wonji-Shoa, Metahara, and Finchaa Sugar Estates with the objective of assessing the status of soil physical and hydraulic properties under long term mechanized sugarcane cultivation by taking uncultivated soils nearby the farms as references. Disturbed composite and undisturbed soil samples from 0-30 layer of selected cultivated and uncultivated light and heavy Soil Management Unit Groups (SMUGs) at Wonji-Shoa and Metahara and; Luvisols and Vertisols at Finchaa were collected for laboratory analysis of selected soil properties. Results of the study indicated that soils under sugarcane cultivation had higher clay contents than uncultivated soils at all the soil management unit groups. The bulk density and total porosity values were out of ranges recommended for optimum sugarcane cultivation for most land uses of the estates. For all the sampled sites, soils under sugarcane had higher available water holding capacity than the uncultivated soils for all soil management unit groups. Available Water Holding Capacity (AWC) of the three estates is above the threshold AWC value ideal for sugarcane cultivation. Very close variations were observed in AWC among the cultivated soil management unit groups. The mean basic infiltration rate value of uncultivated land was greater than the cultivated lands in all the soil management unit groups. Interpretation of infiltration measurements in terms of suitability for furrow irrigation indicated that Finchaa soils are not suitable for furrow irrigation. From these findings one can conclude that long term cultivation of sugarcane induces soil compaction which decreased the total pore space of a soil mainly by increasing fineness of the soils and also number of meso and microspores in all the estates. The existing soil management based on pF2 classes of the three estates is poorly related with soil physical and hydraulic parameters. Thus, irrigation interval, frequency and the amount of water for irrigation presently in use in the three estates are in question. The gradual water releasing behaviors manifested by clay soils of Ethiopian Sugar Estates could be considered as an asset in increasing yield per fields of the estates if accompanied by good soil water managements. Hence, to maintain sustainability of sugarcane production in the three estates; soil management practices that can protect/ameliorate soil compaction and periodic revision of pF2 based soil management units classification are important. Nevertheless, to develop a concrete recommendation and to measure the long term effects of sugarcane cultivation on properties of state soils further research studies are needed.

Keywords: Cultivated soils; Degradation; Hydraulic property; Soil physical property