Mechanical resilience of degraded soil amended with organic matter

Organic matter may help prevent the degradation of the soil pore structure by mechanical stresses, and consequently the impact of compaction and surface erosion. To obtain a mechanistic understanding of some of the processes involved, we amended an Ultisol with peat particles, at amendment rates of 0, 10, and 50 g kg(-1), and subjected the peat-soil mixtures to different wet/dry cycles (1, 4, or 10). Mechanical stresses were imposed to the soil as direct shear, surface shear, and virgin compression tests. The objective was to determine the effect of increasing organic matter on the resistance and resilience of the soil pore structure to mechanical stresses, after wet/dry cycles. Peat amendment increased soil porosity, mainly in the fine pores (< 6 μ m), whereas an increased number of wet/dry cycles affected the coarse pore fraction (> 50 μ m). Soil shear strength decreased with a greater peat-amendment rate. For soil amended with 50 g kg(-1) of peat, increasing the number of wet/dry cycles increased the compressibility index from 1.14 to 1.43 and the friction angle under shear by 6°. Although peat may decrease the resistance to compression, the initial soil pore structure and the resilience to this mechanical stress was greatly improved. Wetting and drying cycles improved the impact of peat on the mechanical resistance of the soil, but reduced resilience slightly. The results suggest that to amend with organic matter will improve recovery from vehicle traffic damage and improve water retention during dry periods, providing better conditions for plants and microbes.