## 3 Results and Discussion
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multicolumn{2}{c}{**Parameter**} & \multicolumn{6}{c}{**Mg Concentration of the Nutrient Solution (mg L\({}^{-1}\))**} \\  & **0** & **12** & **24** & **48** & **96** & **192** \\ \hline \multirow{4}{*}{Mg} & Total amount per plant & 51.11 \(\pm\) 4.78 & 57.95 \(\pm\) 8.79 & 56.74 \(\pm\) 5.05 & 62.90 \(\pm\) 4.13 & 60.36 \(\pm\) 3.62 & 67.84 \(\pm\) 14.21 \\  & (mg) & \(\epsilon^{1}\) & bc & bc & abc & a & a \\  & Use efficiency & 678.76 \(\pm\) 85.06 & 603.15 \(\pm\) 58.88 & 577.54 \(\pm\) 38.50 & 570.14 \(\pm\) 71.95 & 543.60 \(\pm\) 79.17 & 459.11 \(\pm\) 56.08 \\  & (mg d.w./mg Mg) & a & ab & b & b & c \\ \hline \multirow{4}{*}{Ca} & Total amount per plant & 452.23 \(\pm\) 29.74 & 424.06 \(\pm\) 66.37 & 413.49 \(\pm\) 40.40 & 415.99 \(\pm\) 40.79 & 402.01 \(\pm\) 52.79 & 365.95 \(\pm\) 30.06 \\  & (mg) & a & a & a & a & a & a \\  & Use efficiency & 76.21 \(\pm\) 5.01 & 82.71 \(\pm\) 11.31 & 79.15 \(\pm\) 1.35 & 86.55 \(\pm\) 12.23 & 81.56 \(\pm\) 6.09 & 84.11 \(\pm\) 12.42 \\  & (mg d.w./mg Ca) & a & a & a & a & a & a \\ \hline \multirow{4}{*}{K} & Total amount per plant & 331.83 \(\pm\) 15.79 & 318.01 \(\pm\) 35.32 & 298.51 \(\pm\) 18.83 & 337.67 \(\pm\) 29.20 & 311.50 \(\pm\) 19.79 & 209.84 \(\pm\) 25.46 \\  & (mg) & a & b & a & ab & b \\  & Use efficiency & 103.76 \(\pm\) 6.65 & 109.56 \(\pm\) 12.57 & 109.84 \(\pm\) 10.70 & 106.05 \(\pm\) 9.92 & 105.77 \(\pm\) 19.14 & 106.35 \(\pm\) 19.87 \\  & (mg d.w./mg K) & a & a & a & a & a & a \\ \hline \multirow{4}{*}{P} & Total amount per plant & 38.38 \(\pm\) 3.39 & 36.53 \(\pm\) 5.04 & 35.08 \(\pm\) 3.46 & 36.84 \(\pm\) 2.12 & 33.17 \(\pm\) 3.34 & 30.61 \(\pm\) 1.71 \\  & (mg) & ab & ab & ab & bc & bc & c \\  & Use efficiency & 902.10 \(\pm\) 93.76 & 955.95 \(\pm\) 107.57 & 937.03 \(\pm\) 90.52 & 975.18 \(\pm\) 146.43 & 990.64 \(\pm\) 138.35 & 1009.85 \(\pm\) 194.9 \\  & (mg d.w./mg P) & a & a & a & a & a & a \\ \hline \multirow{4}{*}{Mn} & Total amount per plant & 4290 \(\pm\) 290 & 3878 \(\pm\) 350 & 3129 \(\pm\) 443 & 3298 \(\pm\) 238 & 2846 \(\pm\) 372 & 2705 \(\pm\) 273 \\  & (\(\mu\)g) & a & b & cd & c & de & e \\  & Use efficiency & 8.08 \(\pm\) 1.09 & 9.01 \(\pm\) 1.41 & 10.63 \(\pm\) 1.73 & 10.91 \(\pm\) 1.71 & 15.85 \(\pm\) 1.54 & 11.51 \(\pm\) 2.37 \\  & (mg d.w./ mg K) & c & bc & ab & a & a & a \\ \hline \multirow{4}{*}{Zn} & Total amount per plant & 2199 \(\pm\) 91 & 2344 \(\pm\) 228 & 2404 \(\pm\) 80 & 2735 \(\pm\) 227 & 2485 \(\pm\) 58 & 2168 \(\pm\) 227 \\  & (mg) & ab & abc & bc & d & c & a \\ \cline{1-1}  & Use efficiency & 15.65 \(\pm\) 0.92 & 14.95 \(\pm\) 2.70 & 13.66 \(\pm\) 1.76 & 13.22 \(\pm\) 2.48 & 13.15 \(\pm\) 1.58 & 142.52 \(\pm\) 2.15 \\ \cline{1-1}  &Despite the wide range of Mg concentrations (0-192 mg L\({}^{-1}\)) administered to the plants through the nutrient solution, a great difficulty was observed in increasing the concentrations of Mg in the various plant organs, as well as the total amount of Mg absorbed by the plants. These data not only adequately explain the sensitivity of sweet orange plants to Mg deficiency, but also indicate the existence of a root mechanism that strictly controls the absorption of Mg. On the other hand, the fact that the change in the concentration of Mg in the nutrient solution had a more positive effect on the concentrations of Mg in the scion's tissues (mainly in the leaves) than in the rootstock's ones mitigates the difficulty of correcting the shortage of Mg in sweet orange trees by applying fertilizers to the soil. Lack of magnesium impacts nutrient uptake and concentrations in stems, leaves, and roots [19; 22]. According to other findings [23; 27; 45], Mg deficiency may increase the concentrations of other cations, such as Ca, K, and Mn. Our results also support the competitive effect of Mg on Ca uptake. More specifically, the tissues of the scion (leaves, stems) and the roots concentrated considerably less Ca at the presence of 192 mg Mg L\({}^{-1}\), compared to the other Mg treatments (Table 1).