Short-term variations of soil physical properties as a function of the amounts and C/N ratio of decomposing cotton residues. II. Soil compressibility, water retention and hydraulic conductivity

Abstract

There are conflicting reports on the role of soil microfauna and flora on the decomposition of incorporated crop residues and its effects on soil structure. This study examined the temporal changes in soil bulk density, compressibility and hydraulic properties as affected by the amounts of added cotton ( Gossypium hirsutum L.) residues and carbon/nitrogen (C/N) ratios. The work was carried out at constant temperature (25°C) and soil water content (0.18±0.01 g g −1). All the measured properties showed the same trend indicating a transient “flush” of activity between the first and sixth week of incubation, with a sharp maximum (or minimum) in the third week. After 6 weeks these properties again changed direction, and tended towards their initial value. The maxima (minima) are indicative of pore clogging or slime accumulation lowering the hydraulic conductivity and increasing water retention in the 20–75 cm suction, increasing compressibility and lowering tensile strength. These results are consistent with the model of Hadas et al. (1994, Soil Tillage RRes., 32: 183–198). Most of the effect dissipated by Week 6 and was followed by some recovery, which may be due to the activity of a microbial population that their acts more slowly than that responsible for the intial flush, or may have had its initiation inhibited by the first population. Differences between treatments were very minor compared to the above temporal changes found in al the treatments. The sharp changes in properties within a short period after the start of incubation may explain why they were not detected in the field by Rawitz et al. (1989, Final Rep. on BARD project 812, Hebrew Uni. Jerusalem; 1994, Soil Tillage Res., 32: 347–366).