## 3 Results and Discussion
### \(\gamma\)-rays Spectrometry and Penetrometry Surveys
Penetrometry ultrasound measurements were performed in soil depths ranging from 0 to 60 cm and results obtained in the ranges of 0-10 cm, 10-30 cm, 30-45 and 45-60 cm of depth were mapped separately. For the sake of brevity, only 0-10 and 45-60 cm maps have been reported herein (Figure 5C,D). The map of the most surficial layer (0-10 cm of depth) showed generally high cone index (CI) values (average CI value of 2.2 MPa), with 61% of measurements exceeding 2 MPa. These were mainly concentrated in site 1 (Figure 5C). Indeed, as shown by the map in Figure 5C, HZ1 (from A2 to A8 and from B2 to B8 points) had most of the highest CI values (5 MPa) of the layer, while HZ4b (site 2) had the lowest values, ranging from 1 to 2 MPa. Regarding higher depths, in the range of 10-30 cm, CI values increased very rapidly (mean CI value of 2.9 MPa), with 91% of the measurements exceeding 2 MPa. Meanwhile, at 30-45 cm, 99% of CI data exceeded 2 MPa and, among them, 28% of points reached the maximum CI value of 5 MPa. The deepest layer (45-60 cm) \begin{table}
\begin{tabular}{c c c c c c c c c} \hline  & K & U & Th & \(\gamma\)**-Rays Dose Rate** & \multicolumn{4}{c}{**CI**} \\  & \% & mg/kg & mg/kg & nGy/h & \multicolumn{4}{c}{**Mpa**} \\ \hline N. cases & 19 & 19 & 19 & 81 & 81 & 81 & 81 \\ Mean & 2.9 & 8.2 & 17.9 & 97.6 & 2.21 & 2.90 & 3.60 & 3.93 \\ St. Dev. & 0.4 & 1.2 & 2.2 & 11.2 & 0.60 & 0.69 & 1.00 & 1.13 \\ Min & 2.0 & 5.6 & 13.1 & 60.4 & 0.77 & 1.63 & 1.90 & 1.58 \\ Max & 3.6 & 10.4 & 23.0 & 121.9 & 3.46 & 5.00 & 5.00 & 5.00 \\ Coef. Var. \% & 14 & 14 & 12 & 11.5 & 27 & 24 & 28 & 29 \\ Skewness & \(-0.5\) & \(-0.3\) & 0.2 & \(-0.4\) & 0.0 & 0.6 & 0.3 & \(-0.3\) \\ Kurtosis & 0.1 & 0.1 & 1.2 & 0.9 & \(-0.6\) & 1.2 & \(-1.3\) & \(-1.6\) \\ \multicolumn{8}{c}{Pearson correlation coefficients} \\ U & 0.2 & & & & & & & \\ Th & 0.757 ** & 0.284 & - & & & & \\ \(\gamma\)-rays dose & 0.798 ** & 0.685 ** & 0.849 ** & - & \(-0.145\) & \(-0.078\) & 0.103 & \(-0.159\) \\ rate & & & & & & & & \\ \hline \end{tabular}
\end{table} 
Table 2: Descriptive statistics of \(\gamma\)-rays dose rate and penetrometry survey (Cone index (CI)) data at different depths (0–10, 10–30, 30–45 cm). showed a further increase of the CI mean values (3.9 MPa), although in 30% of points, a decrease of CI values was also detected. However, consistent with that observed for the most surficial layer, HZ4b of the 45-60 cm layer showed lower values of CI compared with the shallower areas. It is well known that the shear strength, penetration resistance and hydraulic properties of soils change according to the level of compaction. Both these mechanical and hydraulic properties influence the rate at which plant roots can grow to depth in a soil, and the flow and availability of water and nutrients for plant use. For a given CI, the amount of root growth reduction will vary among plant species and varieties as well as soil types [64]. However, CI classes were selected according to values reported in the literature for root reducing (1 MPa) and restricting (2 MPa) limits [65; 66], defined by study of the percentage of cotton tap roots penetrating 2.5 cm thick layers of soil compacted to different degrees of cone penetration resistance pressures (PR) in four soil types. The range of 1-2 MPa was identified as a state of reducing penetration, 2-3 MPa as a state of restricting penetration, and the 3-5 MPa range was considered a hardened soil, very difficult to penetrate, even for tree roots. Therefore, by the evaluation of the CI maps at different soil depths, a picture of  
Figure 5: \(\gamma\)-rays dose rate and penetrometry ultrasound maps. (**A**) Sampling scheme; (**B**) \(\gamma\)-rays dose rate map; (**C,D**) cone index (CI) maps at 0–10 cm and 45–60 cm. high compaction and degradation of soil physical properties was outlined for the whole studied area, starting from the topsoil.