## 3 Results and Discussion
### Physicochemical Characterisation of Biosolids
From the above, the results established in the literature is confirmed in the sense that biosolids not only contribute organic matter to soils, but also macro and micronutrients that can be used by crops. However, the results obtained from all micronutrients in the evaluated biosolids were significantly different (Fe, F = 314.456, \(p\) = 0.000; B, F = 22.683, \(p\) = 0.002; Mn, F = 144.483, \(p\) = 0.000; Zn, F = 405.291, \(p\) = 0.000; Cu, F = 21.570, \(p\) = 0.003) at different seasons of the year. Confirming the importance of analysing the amount of each of these micronutrients present in biosolids and their evolution over time at the site that has been generated (e.g., UWWTP), as well as after being incorporated depending on the dose of application to the soil. In addition, the quantity of each of these elements required in the soil, as well as in the crops, must also be considered, taking into account the needs of each species to be cultivated in order to maintain a balance of micronutrients suitable both for the soil and for the plants. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multicolumn{4}{c}{**Biosolids Analysed for Each Season of the Year**} \\ \cline{2-5}  & **Spring** & **Summer** & **Autumn** & **Winter** \\ \hline pH & 6.10 \(\pm\) 0.17 a & 6.20 \(\pm\) 0.40 a & 6.17 \(\pm\) 0.17 a & 6.41\(\pm\)0.83 a \\ EC (dS m\({}^{-1}\)) & 5.71 \(\pm\) 1.93 a & 3.38 \(\pm\) 1.25 a, b & 1.60 \(\pm\) 0.01 b & 1.65 \(\pm\) 0.18 b \\ TOC (\%) & 37.25 \(\pm\) 4.37 c & 57.94 \(\pm\) 1.25 a & 50.25 \(\pm\) 0.96 b & 36.90 \(\pm\) 1.17 c \\ TN (\%) & 6.67 \(\pm\) 0.98 a & 6.78 \(\pm\) 0.82 a & 6.59 \(\pm\) 0.47 a & 6.35 \(\pm\) 0.42 a \\ C/N & 5.64 \(\pm\) 0.78 b & 8.64 \(\pm\) 1.18 a & 7.65 \(\pm\) 0.56 a, b & 5.83 \(\pm\) 1.38 b \\ P (\%) & 2.65 \(\pm\) 0.17 a & 1.48 \(\pm\) 0.14 b & 1.76 \(\pm\) 0.03 b & 2.28 \(\pm\) 0.13 a \\ K (\%) & 1.09 \(\pm\) 0.12 a & 0.69 \(\pm\) 0.07 b, c & 0.59 \(\pm\) 0.03 c & 0.86 \(\pm\) 0.04 b \\ Fe (g kg\({}^{-1}\)) \({}^{\intercal}\) & 16.10 \(\pm\) 0.40 c & 39.28 \(\pm\) 1.77 a & 20.43 \(\pm\) 0.59 b & 17.34 \(\pm\) 1.91 c \\ B (mg kg\({}^{-1}\)) \({}^{\intercal}\) & 143.33 \(\pm\) 12.01 b & 145.00 \(\pm\) 8.00 b & 172.62 \(\pm\) 2.13 a & 122.41 \(\pm\) 8.41 b \\ Mn (mg kg\({}^{-1}\)) \({}^{\intercal}\) & 130.00 \(\pm\) 8.00 c & 215.62 \(\pm\) 7.39 a & 166.30 \(\pm\) 4.59 b & 126.85 \(\pm\) 7.56 c \\ Zn (mg kg\({}^{-1}\)) \({}^{\intercal}\) & 778.67 \(\pm\) 13.50 b & 635.65 \(\pm\) 10.55 c & 602.76 \(\pm\) 2.34 d & 813.51 \(\pm\) 10.58 b \\ Cu (mg kg\({}^{-1}\)) \({}^{\intercal}\) & 133.64 \(\pm\) 12.01 a & 112.39 \(\pm\) 5.56 b & 95.22 \(\pm\) 2.84 b & 132.42 \(\pm\) 5.64 a \\ \hline \hline \end{tabular}
\begin{tabular}{l c c c c} \hline \hline EC = Electrical conductivity, TOC = Total organic carbon and C/N = carbon-nitrogen ratio. The values are the mean \(\pm\) standard deviation (3 replicates). Rows with different letters are significantly different according to [PERSON]’s analysis with \(p\leq 0.05\). \({}^{\intercal}\) The units correspond to biosolids on a dry basis.  
\end{table} 
Table 2: Physicochemical characteristics and nutrient content in biosolids collected and evaluated in the urban wastewater treatment plant (UWWTP) at different season of year.