Effect of residue incorporation on physical properties of the surface soil in the South Central Rift Valley of Ethiopia

Soil erosion and moisture stress are the major problems for crop production and sustainable land management in Ethiopia. This study was conducted to determine whether incorporation of crop residues modifies the physical properties of the surface soil by increasing water infiltration and storage, decreasing evaporation rate, and improving soil tilth. The effect of maize (Zea mays L.) residues incorporated at a rate of 6 Mg ha(-1) (with inorganic fertilizer (RF) and without (R)) were compared to applying inorganic fertilizer alone (F) and a control (C) on two soil types (a Mollic Andosol with sandy loam texture and a Dystric Nitosol with clayey texture) in the South Central Rift Valley of Ethiopia. After three (annual) residue incorporations, penetration resistance at the 10 cm depth of both soils and shear resistance at the 5 cm depth of the sandy loam soil were 22-52% lower in the RF and R treatments than in the C treatment. The macro-plus mesoporosity in the RF treatment of the sandy loam soil (0-7 cm depth) was 22% higher compared to that of the C treatment. Evaporative flux (0-20cm depth) in the RF and R treatments of the sandy loam soil and in the R treatment of the clayey soil were lower compared to the C treatment by 39-57%. The results indicate that incorporating crop residues, especially in conjunction with the use of inorganic fertilizers, can improve rain water use efficiency and soil tilth. This will also have a direct effect in minimizing the rate of soil erosion in the area. (C) 2003 Elsevier B.V. All rights reserved.