Soil quality indicators for different restoration stages on Amazon rainforest

• Different restoration stages affect soil quality indicators in the Central Amazon.
• Soil density, N and K distinguished different restoration stages.
• Increasing restoration stages are associated with higher N and K+ soil concentration.

Despite the global importance of Amazon rainforest, few studies have evaluated soil quality indicators (SQI) in this region. This study evaluated 13 SQIs according to their correlation and sensibility to differentiate four areas under different restoration stages in the Brazilian Amazon rainforest: degraded area (DEGR), two restoration areas (REST1 and REST2) and an undisturbed forest (FORE). The different restoration stages had influence on SQIs. Soil bulk density (ρs), total nitrogen (total N) and exchangeable potassium (K+) on soil showed higher number of correlation (P < 0.001; rs > |0.70|) with other SQIs and were sensitive (P < 0.05) to distinguish the different areas. Soil bulk density decreased in the following order: DEGR > REST1 > REST2 > FORE. Otherwise, soil total N decreased on a reverse order: FORE > REST2 > REST1 > DEGR. Increasing restoration status of Amazon rainforest is associated with lower ρs and higher N and K+ concentration on soil.