Soil quality improvement is critical to any rehabilitation programme in dry land degraded ecosystems. This study reports on the impact of cultivation of Jatropha curcas with or without soil amendments on the structural stability, and carbon and nitrogen content of a degraded Entisol under rehabilitation in western India. Cultivation of Jatropha curcas resulted in 11% average increase in mean weight diameter of the soil and 2% increase in soil macro-aggregate turnover. Cultivation of Jatropha curcas with nitrogen and phosphorus-or without any-amendment improved macro-aggregate stability relative to nearby native vegetation. Regression analysis showed a significant correlation between organic carbon and mean weight diameter. The cultivation of Jatropha curcas appeared to have also contributed to the quality of these soils as it maintained organic carbon and nitrogen stock and displayed a potential to increase carbon sequestration rate. Soil structure recovery under cultivation of Jatropha curcas implies a sustainable improvement in the surface integrity of these soils, which will ensure more water infiltration rather than runoff and erosion.

Different land-use affects the organization of mineral soil particles and soil organic components into aggregates and the consequent arrangement of the aggregates will influence essential ecosystem functions. We investigated a continuous rubber plantation (forested), land fallowed for 10 y (fallow), 10-y continuous arable cropping land and cropped land with top soil removed (TSR) for concentrations of C, N, and P in bulk soil and dry aggregates. Results showed that a high level of soil disturbance decreased the proportion of surface (0-15 cm) soil aggregate stability (low mean weight diameter) in TSR by 149% and arable cropping by 125% compared with the forested. Aggregate associated SOC was higher in aggregate-size fractions of forested land-use when compared with that in 10-y fallow, continuous arable cropping, and TSR. For aggregate associated N, fallow and forested land-use types concentrated higher proportion across aggregate sizes than the arable cropping and TSR. Macro aggregate fractions generally contained higher concentrations of C, N, and P compared with the micro-aggregates. Water transmission indicators like total porosity and saturated hydraulic conductivity recorded higher values with forested and fallow land-use than the others. We can thus conclude that long-term soil disturbance due to cultivation and removal of top soil reduces the accumulation of soil C, N, and P in bulk soil and decreases water transmission properties. On the other hand, aggregate-associated C, N and P accumulations are dependent on the level of soil surface disturbance and aggregate sizes.

Quantification of soil physical quality (SPQ) and pore size distribution (PSD) can assist understanding of how changes in land management practices influence dynamics of soil structure, and this understanding could greatly improve the predictability of soil physical behavior and crop yield. The objectives of this study were to measure the SPQ index under two different land management practices (the continuous arable cropping system and natural bush fallow system), and contrast the effects of these practices on the structure of PSD using soil water retention data. Soil water retention curves obtained from a pressure chamber were fitted to van Genuchten's equation, setting m (= 1-1/n). Although values for soil bulk density were high, soils under the continuous arable cropping system had good SPQ, and maintained the capacity to support root development. However, soils under the natural bush fallow system had a worse structure than the continuous arable system, with restrictions in available water capacity. These two management systems had different PSDs. Results showed the inferiority of the natural bush fallow system with no traffic restriction (which is the common practice) in relation to the continuous arable cropping system in regard to physical quality and structure.

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