Effects of rehabilitation strategies on soil aggregation, C and N distribution and carbon management index in coffee cultivation in mined soil

Mining can be considered one of the most impacting activities in the soil, since it requires the removal of the vegetation and superficial soil layer, demanding the later recovery of the area. Given this, in this study, we assess the soil rehabilitation in a bauxite-mined area after three years of the field experiment installation through the determination of the total and labile C and N contents, in addition to the carbon management index (CMI), in soil and in stable aggregates separated into three classes (macro: 4.75-2.0 mm, meso: 2.00-0.25 mm and micro: 0.25-0.053 mm). Among the rehabilitation strategies, different combinations of fertilizations and ground cover plants intercropping with coffee, were evaluated. Results revealed that among all the treatments with fertilization, the highest water-stable macroaggregates (+80%), MWDW (2.86 mm), GMD(W) (2.02 mm), AGRI(W) (81.48%) and SAI(W) (89.21%) in the 0-20 cm soil layer were recorded in organic fertilization + brachiaria treatment (OF/B), close to native vegetation (NV). These indices were characterized as good indicators of macroaggregation and soil quality; however, the mesoaggregates reflected the differences in the dynamics of C and N due to the influence of management systems. In the soil, the plots under organic and chemical fertilization + brachiaria (OF + CF/B) had more TOC (22.11), TN (1.49), LOC (1.44), LN (0.054) g kg(-1), respectively, and CMI (33.06%). Significant effect of the OF + CF fertilization was only observed in aggregate size of meso and microaggregates. TOC and TN contents were higher in the mesoaggregates, but not higher than the soil, however, LOC and CMI had higher values in the macroaggregates, higher than the soil. In general, when OF/B was used, the macroaggregation increased by 27.6%, MWDw (7.51%), the GMDw (48.52%), and OF + CF/B, the TOC (63%) and TN (67%) in relation to the pre-mined area. CMI is very effective in evaluating the best management systems to recover degraded areas, such as areas of mineral extraction, and the best indicators of this index were evaluated in the aggregate classes. The estimation of CMI values and analysis of organic attributes in aggregate classes can be used to ascertain the impacts of management practices and how they aid in the recovery of the physical quality of soil in the rehabilitation phase. The application of the organic and/or organic and chemical fertilization with brachiaria may represent an option for the sustainability of the system by the reconditioning of the organic attributes of the soil in mineral exploration area.