The effect of long-term Maresha ploughing on soil physical properties in the Central Rift Valley of Ethiopia

For thousands of years, smallholder-based crop farming in Ethiopia has been practiced with oxen ploughing using the traditional Maresha ard plough where consecutive tillage operations are undertaken perpendicular to each other. Despite its wide acceptance by smallholder farmers, long-term use of the Maresha is believed to deteriorate the soilʹs physical properties. This study examines the surface and subsurface infiltration, soil evaporation and penetration resistance of sandy loam soils that have been exposed to varying durations (0, 2, 7, 22 and 35 years) of cultivation after being converted from acacia-based grassland dominated by Acacia tortilis and Acacia senegal in the Central Rift Valley (CRV) of Ethiopia. The infiltration rate of the surface layer increased significantly (p = 0.05) immediately after conversion from acacia-based grassland to cultivated land. Thereafter, there was a weak decreasing trend (p > 0.05, R2 = 0.24) in infiltration rate with years of cultivation. Unlike the surface soil layer, there was no significant difference in the subsurface (below 15 cm) infiltration between the acacia-based grassland and lands cultivated for varying numbers of years. Following a rain event satisfying field capacity of the soils, the daily soil evaporation increased significantly (p = 0.05) with increased duration of cultivation. The cumulative evaporation, observed over 5 consecutive days following the last rainfall, increased by 2.4 times in the 35 years old cultivated land from the acacia-based grassland. There was also a strong correlation (R2 = 0.86) between α (the slope of the cumulative evaporation versus the square root of time) and an increase in the years of cultivation. It is, therefore, concluded that long-term Maresha cultivation along with the present soil management makes the maize crop susceptible to drought and dry-spells. Improved soil management and development of appropriate tillage are needed to maximize rainwater use efficiency and achieve a more sustained agricultural production in the drought-prone CRV of Ethiopia.