# Soil Quality in Rehabilitated Coal Mining Areas
## 3 Results  
### Soil Organic Matter, Microbial Biomass Content and Water Stable Aggregates  
The analyses of the thermographs show three peaks of weight loss, corresponding to three temperature ranges (210-375 \({}^{\circ}\)C, 430-580 \({}^{\circ}\)C, and 650-850 \({}^{\circ}\)C) that we attributed to organic matter, coal, and calcium carbonate, respectively. These ranges were used to quantify these three fractions by thermogravimetry.  
The Dumas and calcination methods for SOC analyses yielded the highest values (Table 4), while the ones obtained by thermogravimetry were the lowest (Table 4).  
The trend on microbial carbon biomass showed that the plots with sludge presented the highest values except when additional slurry was applied on the surface (Table 4). In this latter case (wSwP) no differences could be found with plots without sludge, irrespective of the proportion of material in the substrate (1:1 or 1:2).  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Plot 2 Reference** & **Cmb (mg kg\({}^{-1}\))** & **CaCO3 eq** & **Cdry** & **Ccal** & **Cwet** & **CO3\({}^{2-}\)T** & **COT** & **CminT** \\ \hline wSwP 1:3:1 (1-F) & 703 (27) c & 521 (13) cd & 167 (3) a & 156 (6) a & 102 (6) b & 341 & 34 & 7 \\ wSwP 1:3:1 (2-F) & 319 (74) eg & 543 (21) bc & 171 (4) a & 156 (3) a & 109 (3) a & 365 & 36 & 9 \\ wSwP 1:3:1 (3-F) & 798 (45) b & 528 (20) bcd & 166 (4) a & 154 (7) ab & 101 (2) b & 297 & 38 & 9 \\ wSwP 1:3:1 (4-F) & 336 (29) ef & 517 (13) bcd & 167 (5) a & 151 (7) ab & 107 (4) a & 346 & 37 & 10 \\ wSnP 1:3:1 (5-F) & 896 (37) a & 533 (17) bc & 157 (5) b & 149 (4) ab & 100 (2) b & 348 & 41 & 8 \\ wSwP 1:3:1 (6-F) & 317 (77) eg & 554 (30) ab & 166 (3) a & 156 (2) a & 88 (2) c & 348 & 35 & 8 \\ nSwP 1:1 (7-F) & 314 (36) eg & 548 (25) bc & 156 (7) b & 155 (3) a & 71 (1) e & 343 & 27 & 9 \\ nSwP 1:2 (8-F) & 378 (34) e & 504 (16) d & 157 (4) b & 156 (2) a & 76 (3) d & 352 & 26 & 2 \\ nSnP 1:1 (9-F) & 272 (41) fg & 526 (20) bcd & 158 (5) b & 150 (9) ab & 68 (1) e & 341 & 26 & 8 \\ nSnP 1:2 (10-F) & 287 (65) fg & 581 (5) a & 165 (4) ab & 146 (2) b & 76 (3) d & 376 & 25 & 7 \\ \hline \hline \end{tabular}  
* Averages of every two groups being compared without any letter in common are different (\(p\)-values \(<\) 0.05) according to Student’s \(t\)-test. 2 Plot references are described in Table 3. The order in a column (number in brackets) matches the sequence, from north to south, of west-oriented field plots.  
\end{table}
Table 4: Averages 1 plus standard deviation (numbers in brackets) in each plot 2 of carbon microbial biomass (Cmb), calcium carbonate equivalent (CaCO3 eq), carbon by dry combustion (Cdry), carbon by calcination at 560 \({}^{\circ}\)C (Ccal), and carbon by wet oxidation (Cwet). Carbon fractions by thermogravimetry (one sample per plot): carbonates (CO3\({}^{2-}\)T), organic-C (COT), and mineral-C (CminT) are also included.  
When organic carbon data from thermogravimetry and plots with sludges (1:3:1 plots) were compared with data from plots without sludges (the rest), the former presented a significantly higher organic content (37 g kg\({}^{-1}\)) than the rest (26 g kg\({}^{-1}\)). They also showed significantly higher water-stable aggregates (Table 5). However, bulk density showed erratic variability, with values ranging from 1.11 Mg m\({}^{-3}\) up to 1.30 Mg m\({}^{-3}\) (Table 5).