Changes in Soil Organic Pool and Carbon Preservation Capacity of Macro- and Micro-aggregates in Response to Land-Use Change in North-Western India

Soil aggregate stability is considered feasible and important indicator for understanding complex interactions between soils' physico-chemical and biological properties and soil structure. The present study was therefore, conducted to find out the land-use change induced alteration in soil organic carbon (C) pool in response to changed restored engineering. The present study was conducted to reveal the distribution of water stable aggregates, aggregate stability, aggregate associated C of macro-and micro-aggregates, C preservation capacity of aggregate, and the labile and non-labile C fractions of variable oxidizability due to land-use change from the uncultivated soils to under rice-wheat, seed sugarcane, ratoon sugarcane and permanent grasslands in north-western India. These results showed that water stable aggregates, macro-and micro-aggregates, C preservation capacity, aggregate ratio and total organic carbon (TOC) stocks were significantly (p < 0.05) higher in permanent grassland and uncultivated soils. Ratoon sugarcane soils had similar to 10.3% higher TOC pool than the seed sugarcane. A significant decrease in TOC pool by similar to 11.3-11.9% occurred in soils under seed sugarcane cultivation, compared to others. Soils under seed sugarcane had similar to 11.5% lower C stocks, compared with the rice-wheat soils. As compared with the uncultivated soils, highest C loss of 3.3-3.7 Mg C ha(-1) occurred in soils under seed sugarcane, followed by almost equal in rice-wheat (1.9-2.0 Mg C ha(-1)) and ratoon sugarcane (1.9-2.1 Mg C ha(-1)). The greatest C loss in soils under seed sugarcane was ascribed to increased tillage intensity. More intensified tillage under seed sugarcane cultivation resulted in decreased proportion of macro-aggregates (> 0.25 mm) and greater stabilization of organic C in relatively recalcitrant C pool as compared to those under ratoon sugarcane. Active C (Fract. 1 + Fract. 2) pool in surface soil layer under ratoon sugarcane was significantly higher by similar to 25.1-64.9%, compared with others. Conversely, the passive C pool (Fract. 3 + Fract. 4) was significantly lower in soils under seed sugarcane, while the highest in grassland. The proportion of macro-aggregates in soils under different land-use systems exhibited a linear significant relationship with the TOC pool (R-2=0.964*; p < 0.05). Soils under seed sugarcane have significantly lower C preservation capacity of macro-aggregates by similar to 42.5%, compared with the ratoon sugarcane. Rice-wheat ecosystem had significantly higher C preservation capacity of macro-aggregates (> 0.25 mm) by similar to 0.70 g C kg(-1) soil (similar to 80.5%) than the seed sugarcane. The sensitivity index showed significantly higher sensitivity of TOC pool for soils under seed sugarcane (by similar to 8.6-21.8%), followed by ratoon sugarcane (similar to 10.3-13.6%) and rice-wheat (similar to 7.6-11.8%), while the lowest for grassland ecosystems (similar to 0.2-0.5%) following the land-use change from uncultivated lands. Among the three cropland ecosystems, C preservation capacity of macro-aggregates was significantly higher than the sugarcane-based ecosystems. Considering uncultivated lands as reference, the soils under ratoon sugarcane had significantly higher C management index (CMI) than the other compared land-use systems. The highest values of the CMI in soils under ratoon sugarcane indicate C rehabilitation, while the lower values for seed sugarcane indicate C degradation. We put forward general management suggestions for different land-use and focus on better measures for the management of rice-wheat and seed sugarcane to reduce C losses by increasing aggregate stability of soils under different land-use systems.