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Mechanical Resilience of Degraded Soil Amended with Organic Matter

^a Institute of Soil Science, Chinese Academy of Sciences, P.O. Box 821, Nanjing, 210008, People's Republic of China
^b Institute of Plant Nutrition and Soil Science, CAU, 24118 Kiel, Federal Republic of Germany
^c Plant-Soil Interface Programme, Scottish Crop Research Institute, Invergowrie, Dundee, DD2 5DA Scotland, UK

View larger version (29K): [in a new window]   Fig. 1. Total porosity of the 0-, 10-, and 50-g kg–1 peat-amended soils after 0 (blank), 1 (slashed), 4 (crossed), and 10 (grayed) wet/dry cycles. The standard error is shown (n = 4).

View larger version (28K): [in a new window]   Fig. 2. Equivalent pore-size distribution of the 0-, 10-, and 50-g kg–1 peat-amended soils after 1 (blank), 4 (slashed), and 10 (crossed) wet/dry cycles. The standard error is shown (n = 4).

View larger version (21K): [in a new window]   Fig. 3. Soil settlement (upper) and soil water potential (lower) of the 50-g kg–1 peat-amended soil after one wet/dry cycle after application and release of 200 kPa-applied stress in the compression test.

View larger version (19K): [in a new window]   Fig. 4. Void ratio against the applied stress for the 10-g kg–1 (upper) and 50-g kg–1 (lower) peat-amended soils after 1 (square), 4 (circle), and 10 (triangle) wet/dry cycle(s) at –30-kPa water potential. The standard error is shown (n = 3). S.d. indicates significantly different between wet/dry cycles.

View larger version (18K): [in a new window]   Fig. 5. The compressibility index of the 10-g kg–1 (left) and 50-g kg–1 (right) peat-amended soils after different wetting and drying (wet/dry) cycles at –30-kPa water potential.

View larger version (41K): [in a new window]   Fig. 6. Rebound height after stress release for the 10-g kg–1 (left) and 50-g kg–1 (right) peat amended soils after 1 (blank), 4 (slashed), and 10 (crossed) wet/dry cycles. The standard error is shown (n = 3).

View larger version (54K): [in a new window]   Fig. 7. Pore water potentials of the 10-g kg–1 (upper) and 50-g kg–1 (lower) peat-amended soils before (blank) and after (crossed) application of compressions, and after removal of compression (crossed) as affected by 1 (left), 4 (middle), and 10 (right) wet/dry cycles. The standard error is shown (n = 3).

View larger version (39K): [in a new window]   Fig. 8. A conceptual diagram of how peat amendment and wet/dry cycles influence soil structure and mechanical behavior. At the top of the figure, the lightly textured blocks represent soil aggregates and the thick lines peat. At the bottom of the figure, the size of the spring represents elastic deformation that is recoverable once the stress, is removed. The size of the dashpot represents plastic deformation that is not recoverable when the stress is removed. Aggregation increases with number of wet/dry cycles, leading to coarser pores that are more easily compressed but not recovered on unloading. The peat particles fill in coarse pores and move apart soil aggregates, causing a higher total porosity and fine pore-size fraction. Peat acts as an elastic spring, but with number of wet/dry cycles the impact diminishes as some peat becomes physically protected in soil aggregates.