3.2.2. Other Nutrients

*Phosphorus.* For P, amendments and time showed significant differences (Table 3). The P supply rate was significantly lower (−24%) in the willow treatment than in the miscanthus treatment and the control (Figure 7, left). In addition, the P supply rate varied over the lettuce growth period (Figure 7, right).

**Figure 7.** P supply rates as a function of amendment (**left**) and time (resin sampling period) (**right**). Different letters indicate significance at *p* < 0.05 using the *post hoc* Tukey HSD test.

*Potassium.* For K, only the PRS® probe sampling period showed a statistically significant difference, with a decrease over time (Table 3, Figure 8). From the beginning to the end of lettuce growth, K supply rates decreased by 30%.

**Figure 8.** K supply rates as a function of time (resin sampling period). Different letters indicate significance at *p* < 0.05 using the *post hoc* Tukey HSD test.

*Calcium.* For Ca, sampling zone, time, amendment X time, and sampling zone X time all showed significant differences (Table 3). Although the amendment X time interaction was significant, it was not relevant from a practical point of view, as, for example, the control in the first sampling period differed from the miscanthus in the fifth sampling period. Ca supply rates decreased by an average of 30% across amendments and sampling zones from the beginning to the end of lettuce growth (Figure 9). In addition, the average difference between root zone and bulk soil sampling was 10%; the decrease in the root

zone was significant for resin sampling periods 3 and 4, with differences of 18% and 17%, respectively, between the root zone and the bulk soil (Figure 9).

**Figure 9.** Ca supply rates as a function of sampling zone and time. Different letters indicate significance at *p* < 0.05 using the *post hoc* Tukey HSD test.

*Magnesium.* The behavior of Mg closely followed that of Ca. Sampling zone, time, amendment X time, and sampling zone X time all showed significant differences (Table 3). As mentioned above for Ca, the amendment X time interaction was significant but not relevant in practical terms. Mg supply rates decreased by an average of 18% across amendments and sampling zones by the end of lettuce growth (Figure 10). In addition, the average difference between root zone and bulk soil sampling was 12% and the decrease was significant for the third resin sampling period, with a 21% difference between the root zone and the bulk soil (Figure 10).

*Sulfur.* S supply rates differed significantly by amendment, sampling zone, time, and interaction between sampling zone and time (Table 3). The S supply rate increased significantly in both the miscanthus (+38%) and the willow (+59%) treatments (Figure 11, left). Overall, the S supply rate increased by 42% from the beginning to the end of lettuce growth and was 18% higher in the bulk soil than in the root zone. However, there was a significant interaction between the period and sampling zone, and the S supply rate was significantly higher in the bulk soil compared to the root zone in the fourth resin sampling period (Figure 11).

*Iron.* For Fe, sampling zone, time, and sampling zone X time all showed significant differences (Table 3). On average, Fe supply rates decreased by 43% across amendments and sampling zones from the beginning to the end of lettuce growth (Figure 12). In addition, the average difference between root and bulk soil sampling was 32%. The interaction between time and sampling zone showed that in the fourth period of resin sampling, the Fe supply rate was significantly higher (+244%) in the root zone as compared to the bulk soil (Figure 12).

*Manganese.* The behavior of Mn closely followed that of Fe. Sampling zone, time, and sampling zone X time all showed significant differences (Table 3). Mn supply rates had decreased by an average of 47% across amendments and sampling zones by the end of lettuce growth (Figure 13). In addition, the average difference between root zone and bulk soil sampling was 26%. The interaction between time and sampling zone showed

that in the fourth and fifth resin sampling periods, Mn supply rates in the root zone were, respectively, 125% and 93% higher than in the bulk soil (Figure 13).

**Figure 10.** Mg supply rates as a function of sampling zone and time. Different letters indicate significance at *p* < 0.05 using the *post hoc* Tukey HSD test.

**Figure 11.** S supply rates as a function of amendment (**left**) and interaction between sampling zone and time (**right**). Different letters indicate significance at *p* < 0.05 using the *post hoc* Tukey HSD test.

*Copper.* Cu supply rates differed significantly by sampling zone and time (Table 3). Overall, Cu supply rates were 24% higher in the root zone than in the bulk soil (Figure 14, left). In addition, a significant decrease (50%) was observed between the beginning and the end of lettuce growth (Figure 14, right).

*Zinc.* Zn supply rates differed significantly by sampling zone and time (Table 3). Overall, Zn supply rates were 96% higher in the root zone than in the bulk soil (Figure 15, left). In addition, a significant decrease (61%) was observed between the beginning and the end of lettuce growth (Figure 15, right).

**Figure 12.** Fe supply rates as a function of sampling zone and time. Different letters indicate significance at *p* < 0.05 using the *post hoc* Tukey HSD test.

**Figure 13.** Mn supply rates as a function of sampling zone and time. Different letters indicate significance at *p* < 0.05 using the *post hoc* Tukey HSD test.

**Figure 15.** Zn supply rates as a function of sampling zone (**left**) and interaction between sampling zone and time (**right**). Different letters indicate significance at *p* < 0.05 using the *post hoc* Tukey HSD test.
