Compressibility of soils in a long term field experiment with intensive deep ripping in Romania

Laboratory compressibility tests were done on soil samples taken from a field experiment 21 years old, located on a Stagnic Luvisol, with deep ripping performed with various frequencies: no ripping, ripping every 8. 4 and 2 years, and ripping yearly. Precompression stress was found to increase with depth of the soil profile down to some 60 cm, and somewhat decreasing at the depth of 70-75 cm, which corresponds to the Bt horizon. Due to ripping, the values of the precompression stress decreased: for soils from experimental treatments with different periodicity of ripping operations, the differences were small, and not in a very definite direction. The estimation procedures suggested by Lebert to predict precompression stress for "normal" arable soils could not be applied to ameliorated soil samples investigated in this paper because repeated ripping prevents a continuous aggregate formation and results mainly in structural texture dependent relations. The compression index showed an increase down to 60 cm and a decrease in the Bt horizon (70-75 cm). In the different experimental treatments, it showed a less clear variation, although some trend of increasing with increased number of rippings may be considered. As inferred from these parameters, soil strength and compressibility do not affect directly crop yields. (C) 2000 Elsevier Science B.V. All rights reserved.