Dobrudzha Agricultural Institute, BG-9520 General Toshevo, Bulgaria
YANKOV, P., 2009. Changes in the composition and water sustainability of soil units under the effect of some soil tillage systems. Bulg. J. Agric. Sci., 15: 393-399
The investigation was carried out during 2003-2008 in the trial field of Dobrudzha Agricultural Institute on slightly leached chernozem soil type. A stationary field trial investigated the effect of some soil tillage systems (plowing at 24-26 cm - plowing at 14-16 cm; plowing at 24-26 cm - disking at 10-12 cm; disking at 10-12 cm - disking at 10-12 cm; no tillage - no tillage; cutting at 26-24 cm - cutting at 8-10 cm) on the composition and water sustainability of the structural soil units. Soil samples were taken after harvesting of wheat from the 0-10, 10-20 and 20-40 cm layers. Soil structure was determined through dry and wet screening of soil to find out the percent of the structural soil units of different size (>5, 5-3, 3-1, 1-0.25 and <0.25 mm). The systems involving annual tillage with plowshare destabilized the soil units and decreased the percent of water sustainable soil units along the entire depth of the cultivated profile. The constant shallow tillage done with disk clod-breaker at the same depth deteriorated soil structure in the surface layer. The low degree of crumbing at cutting and the elimination of the mechanical impact at minimal (below 10 cm) and no tillage in combination with decreased mineralization processes as a result from reduced air circulation lead to the decrease or the lack of destructive effect of these soil tillage systems on the soil units. In the lower plow layer, restructuring and increasing of the water sustainable soil units was observed at these types of soil tillage.