# Carbon Storage Potential and Carbon Dioxide Emissions from Mineral-Fertilized and Manured Soil
## 4 Discussion  
### Soil Organic Carbon  
Long-term differentiated mineral and organic fertilization led to significantly different contents of the SOC and TN in the soils from the two treatments investigated in this study. After 91 years of organic fertilization with manure, the content of the SOC in the Ca + M (10.625 g C kg\({}^{-1}\)) of the Ap horizon exceeded that of the treatment supplemented with mineral fertilizers (CaNPK) by 86.9% (5.685 g C kg\({}^{-1}\)) (Table 1). This implies that, during the 91 years of manure supply, the accumulation of the SOC in the Ap, E, and Bt horizons of a loamy sand soil increased on average by approximately 54.9, 5.2, and 11.7 mg C kg\({}^{-1}\) y\({}^{-1}\), respectively, when using the mineral-fertil soil as a reference (CaNPK). The historical \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Year**} & \multicolumn{3}{c}{**Soil Organic Carbon**} & \multicolumn{3}{c}{**Spring**} & \multicolumn{3}{c}{**Autumnumn**} \\ \cline{3-10}  & & \multicolumn{3}{c}{**Soil Organic Carbon**} & \multicolumn{3}{c}{**Dissolved Organic Carbon**} & \\ \cline{3-10}  & & **Ap** & **E** & **Bt** & **Ap** & **E** & **Bt** & **Ap** & **E** & **Bt** \\ \hline
1 st & CO\({}_{2}\)–C soil & 0.79 \({}^{*}\) & 0.90 \({}^{*}\) & 0.71 \({}^{*}\) & 0.94 \({}^{*}\) & 0.64 \({}^{*}\) & 0.86 \({}^{*}\) & 0.75 \({}^{*}\) & 0.75 \({}^{*}\) & 0.78 \({}^{*}\) \\
2 nd & emission & 0.81 \({}^{*}\) & 0.74 \({}^{*}\) & 0.66 \({}^{*}\) & 0.63 \({}^{*}\) & 0.70 \({}^{*}\) & 0.79 \({}^{*}\) & 0.68 \({}^{*}\) & 0.67 \({}^{*}\) & 0.66 \({}^{*}\) \\ \hline \hline \end{tabular}  
* \({}^{*}\)_p \(<\) 0.05. Soil horizons: Ap (0-25 cm), E (26–45 cm), and Bt (<45 cm)._  
\end{table} 
Table 4: Correlation coefficients describing the relationship between the cumulative CO\({}_{2}\)–C soil emissions and the soil organic content and dissolved organic carbon soil content in the Ap, E, and Bt soil horizons in the spring and autumn. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Crop Part** & **Treatment** & **1 st Year Yields (t ha\({}^{-1}\))** & **2 nd Year Yields (t ha\({}^{-1}\))** \\ \hline \multirow{2}{*}{Grain} & CaNPK & 2.76 \({}^{b}\)\(\pm\) 0.17 & 3.04 \({}^{b}\)\(\pm\) 0.21 \\  & Ca + M & 2.39 \({}^{a}\)\(\pm\) 0.23 & 2.37 \({}^{a}\)\(\pm\) 0.20 \\ \hline \multirow{2}{*}{Straw} & CaNPK & 2.94 \({}^{A}\)\(\pm\) 0.09 & 2.31 \({}^{B}\)\(\pm\) 0.11 \\  & Ca + M & 2.83 \({}^{A}\)\(\pm\) 0.27 & 1.87 \({}^{A}\)\(\pm\) 0.08 \\ \hline \hline \end{tabular}  
Mean value \(\pm\) standard deviation (SD). The means followed by different letters in the column (separately for crop part: grain (a, b) and straw (A, B)) are significantly different (_p_ \(<\) 0.05).  
\end{table} 
Table 5: Rye grain and straw yields. data (showing that in the soil samples taken in 1931, the carbon content was 5.68 g kg\({}^{-1}\)) allowed for a realistic estimate of the carbon sequestration in both soils. The topsoil (Ap) of the long-term manured (Ca + M) loamy, sandy soil accumulated approximately 200 kg C ha\({}^{-1}\) y\({}^{-1}\), whereas for the mineral fertilization system (CaNPK), it remained almost constant. This means that plant residues remaining in the soil fertilized only with mineral fertilizers might have kept the content of the SOC in the soil at a relatively constant level. Nitrogen supplied annually with mineral fertilizers can intensify the mineralization processes of the soil organic matter, thus not promoting carbon accumulation in the soil of the CaNPK treatment. The obtained results corresponded with the data from several long-term European experiments. [PERSON] et al. [36] analyzed the data from 20 long-term European experiments in different soil, climatic, and agro-technical conditions. The sites varied in average annual temperatures (from 8.1 to 15.38 \({}^{\circ}\)C), annual precipitation (from 450 to 1400 mm), and soil clay content (from 3 to 31%). Predominately, the content of the SOC in the manured soils was higher than in the mineral-treated soils.