Impact of tillage duration under different cropping systems on selected soil properties of irrigated vertisols, Sudan

Tillage (sub-soiling, disc ploughing, disc harrowing, leveling and ridging) duration under different cropping systems may have various effects on soil properties (physical and chemical). Therefore, could be a useful guide of soil quality indices under cultivation. This study was conducted to determine the effects of long-(79 year), medium-(59 years), and short-term (24 years), tillage on selected chemical and physical soil properties in the cultivated areas of the upper part of the central clay plain (CCP) of Gezira Managil and Rahad schemes, respectively. Representative soil samples were collected from three peons in each scheme at depths from the 0-10, 10-20, 20-30, 30-50, 50-70, and 70-90 cm. For comparison, similar sampling sequence was taken from a non- ploughed (control) plot located at Gezira scheme. Analysis performed were pH, organic carbon, bulk density, hydraulic conductivity, aggregate stability, porosity, particle size distribution, and water holding capacity. Results showed that, there wer no significant differences between croppping systems in bulk density, hydraulic conductivity and aggregate stability. Long and medium-term tillage of Gezira and Managil schemes had significantly (P0.01) increased the content of sand (9.6-13.9%) in the topsoil (0-10) compared to short-term tillage of Rahad (5.5%) by about (74.5 to 162.7%). However, in the same depth, tillage in the Gezira and Managil schemes significantly (p0.001) leached down clay particles from 79.5% to 62.9-69.5%. Generally, water holding capacity followed similar trend to that of clay content. Under all sites, cultivation significantly (p0.01) decreased soil pH in the top 30 cm depth compared to unploughed plots. It was also found that, tillage significantly (p0.02) decreased organic carbon in the top 0-10 cm from 0.18% to 0.08% (Gezira), 0.17% (Rahad) and 0.12% (Managil). Due to high variability (C.V ranged from 32-153%), water holding capacity, hydraulic conductivity and aggregate stability were not significantly different between cropping systems. It could be concluded that under the heavy textural clay soil of the location in the dry tropics, tillage mieght subject the topsoil (plough layer) to depletion of clay and organic matter, thereby, rendering the surface layer to degradation