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Food demand and soil sustainability have become urgent issues recently because of the global climate changes. This study aims to evaluate the application of a biochar produced by rice hull, on changes of physiochemical characteristics and erosion potential of a degraded slopeland soil. Rice hull biochar pyrolized at 400°C was incorporated into the soil at rates of 2.5%, 5%, and 10% (w/w) and was incubated for 168 d in this study. The results indicated that biochar application reduced the Bd by 12% to 25% and the PR by 57% to 92% after incubation, compared with the control. Besides, porosity and aggregate size increased by 16% to 22% and by 0.59 to 0.94 mm, respectively. The results presented that available water contents significantly increased in the amended soils by 18% to 89% because of the obvious increase of micropores. The water conductivity of the biochar-amended soils was only found in 10% biochar treatment, which might result from significant increase of macropores and reduction of soil strength (Bd and PR). During a simulated rainfall event, soil loss contents significantly decreased by 35% to 90% in the biochar-amended soils. In conclusion, biochar application could availably raise soil quality and physical properties for tilth increasing in the degraded mudstone soil.

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To elucidate the properties of pedogenic Cr and Ni in serpentine soils in terms of mobilization, three pedons on the shoulder (Entisol), backslope (Inceptisol). and footslope (Alfisol) along a toposequence in eastern Taiwan were examined for metal partitioning and their geochemical origins. The analysis combined bulk soil analysis by selective sequential extraction (SSE) with mineralogical methods, including x-ray diffraction (XRD) and scanning electron microscopy/energy dispersive x-ray spectroscopy (SEM/EDX) analyses. Experimental results showed that Cr and Ni were mainly concentrated in chromites and silicates, respectively, and were gradually exposed by weathering of the parent materials. The SEM/EDX analysis indicated that chemical modification of the chromites was more prevalent near the soil surface and that the chemical modification increased as available Cr content increased from the shoulder to the footslope. Landscape position was the most important factor in controlling the trends in Ni and Cr fractions. The footslope accumulated more total Cr and Ni than the shoulder and backslope. Additionally the soil on the footslope received more effective precipitation as run-on water from upslope and was potentially more leached than the soils on the other landscape positions. The accumulation of clay and dithionite-citrate-bicarbonate (DCB) extractable Fe (Fej) and the increase of exchangeable Ca/Mg ratio correlated with the increased total labile pools of Cr and Ni in the soil from the shoulder and backslope to the footslope. However, the concentrations of acid soluble, reducible, and oxidizable fractions (total labile pool) of Ni were higher than those of Cr, indicating diat Ni was more available than Cr in all soils tested by the SSE procedures.Abbreviations: BCR.European Community Bureau of Rcferenc; BSE. back-scattered electron; BSP, base saturation percentage; CEC, cation-exchange capacity; DCB, ditbionite-citrate-bicarbonate ; EDX, energy dispersive x-ray spectroscopy; FAAS.flame atomic absorption spectrophotometer; OC. organic carbon; SEM. scanning electron microscopy: SSE. selective sequential extraction: XRD. x-ray diffraction; XRF, x-ray fluorescence.

Biochar promotes the storage of organic carbon (OC) in soils. OC is unevenly distributed in soils among different particle‐size fractions showing different structures, functions, and stability. The objective of this study was to investigate the biochar–soil interactions and the redistribution of soil C in different soil fractions based on a 2‐year field experiment. Fractionation was done by particle sizes including coarse sand (250–2,000 μm), fine sand (53–250 μm), and silt/clay (<53 μm). Integrated spectroscopic techniques were employed to examine physical characteristics of biochar–soil interactions in different soil fractions. Application of biochar increased OC by 37%, 42%, and 76% in soil particle‐size fractions of 53–250, <53, and 250–2,000 μm, respectively. This was supported by X‐ray fluorescence spectroscopy analysis, which showed an increase of C contents by 5–56% with biochar addition. The highest increment in OC was found in coarse sand fraction, and redistribution of OC was detected depending on various soil particle sizes. Results of scanning electron microscopy combined with electron dispersive X‐ray spectroscopy analysis showed the interactions between soil and biochar, which could be attributed to oxidized functional groups (OCO, CO, and CO) captured by the X‐ray photoelectron spectroscopy. The long‐term aged biochar could be beneficial to enhance soil quality by promoting OC storage and facilitating positive biochar–soil interactions.