Soil carbon sequestration as affected by slope aspect under restoration treatments of a degraded alfisol in the Indian sub-tropics

Rehabilitation of degraded lands needs appropriate mix of land use and erosion control measures, and is often associated with carbon (C) sequestration in the soil profile. However, topographic attributes play a deterministic role in the rate of C accretion in degraded sloping lands. This study was carried out to assess the effect of slope aspect on soil C sequestration, soil aggregation and soil moisture retention in aggradation phase of a denuded land in eastern India. Eight treatments of horti-silvi-pastural system integrated with in-situ moisture conservation were taken in randomized block design during 2000 to 2006. Indigofera teysmanni was taken as the silviculture component and hedgerows of the species were used uniformly for all the treatments. A significant interaction effect of the rehabilitation system and slope aspect was observed for residual soil moisture content, soil organic C (SOC) content, SOC stock, size distribution of aggregates and C content in aggregate fractions. Treatments with trenches of 0.45×0.45×1.0m dimension at 0.5mu/s of fruit plants conserved significantly higher soil moisture even at 87mm of evaporativity. On an average, the north facing (NF) aspect had 1.13 and 0.75g 100g−1 higher soil moisture than the east facing (EF) aspect in the 0–15cm and 15–30cm soil depths, respectively. The SOC concentration was higher by 11–12% in the NF than the EF aspect. In the 0–30cm soil profile, the SOC stock varied from 31.55 to 37.91Mgha−1 in the EF aspect and from 35.01 to 41.28Mgha−1 in the NF aspect, as compared to the initial stock of 18.19 and 19.06Mgha−1 in the two aspects, respectively. The NF aspect had 0.35 to 3.17Mgha−1 higher SOC stock in the 0–15cm soil, 0.64 to 3.03Mgha−1 in the 15–30cm soil and 1.85 to 4.59Mgha−1 in the whole 0–30cm soil profile. Averaged over all the rehabilitation systems, the NF aspect accumulated extra C to the tune of 0.19, 0.18 and 0.36Mgha−1yr−1 than the EF aspect in the 0–15, 15–30 and 0–30cm soil layers, respectively. Under all the systems and slope aspects, small macroaggregates (>250μm) constituted the highest proportion, with values varying from 50.4–65.4% in the EF to 61.7–71.7% in the NF aspect. The C content in small macroaggregates was also higher than that in microaggregates and silt+clay size fractions. The study indicates slope aspect to be a significant factor in soil C sequestration, which also affects the aggregation pattern of soils under recovery.