GNGTS 2014 - Atti del 33° Convegno Nazionale

has determined a decrease in soil electrical resistivity especially in the first layer; conversely, for the deeper layers, lowest electrical resistivity values were observed and consistent with the ones recovered at ERT1 survey. The ERT 2 outcome permitted to provide the indication that 38 mm of water irrigation was suitable to satisfy the needs of the crop avoiding undesired waste water by infiltration. The percentage relative changes between resistivity sections ERT2 and ERT1, shown in the lower panel of Fig. 2, is negative in the first layer between 0 and 0.4 m, and positive in the deeper layers. This confirms that only a limited percolation of irrigation water occurred. Moreover, the transition from negative to positive resistivity change is observed in correspondence of the middle soil layer (0.5-0.6 m depth).We compared the radargrams obtained by GPR surveys with ERT images performed at the soil surface in transects longitudinal and parallel with the bean rows so to characterize the same soil profile. A SIR 2000 Radar System equipped with a monostatic antenna at 400MHz central frequency was deployed for the GPR surveys. GPR data were acquired in continuous mode, with a time range equal to 100 ns for the 400 MHz antenna. GPR datasets were first analysed using the REFLEX- Win Version 5.0.5 program (Sandmeier, 2001). Standard data processing has the aim to improving the “imaging” by correctly locating and focusing all the reflectors. The processing was performed according to several steps and the result of the standard data processing is shown in Fig. 3 for the same profile shown by the ERT images in Fig. 2. In Fig. 3a, the GPR radargram acquired with antenna of 400 MHz before irrigation, shows horizontal and parallel layers in the tilled shallower zone, between 0.0 m and 0.30 m depth. At about 0.30 m depth, radargram shows an horizontal and continuous reflector attributed to the presence of a more compacted soil layer and identified as plow layer created by repeated tillage at same depth. In the deeper layers, many distinguishable reflectors are visible, probably due to the presence at vary levels of stoniness; finally, the water table was observed at about 1.0 m depth. Fig. 2 – Soil section inverted electrical resistivity measured just before irrigation (ERT1) and 24 hours after irrigation (ERT2). Soil inverted resistivity section change between ERT2 and ERT1 (bottom). GNGTS 2014 S essione 3.3 231