A total of eighty pots filled with SAP-amended soil were prepared. Figure 1a,b show a schematization
and a picture of the experimental setup, respectively. As can be seen from Figure 1a, four sets of samples
were prepared: two sets were planted with chicory and two sets with tomatoes. Each set consisted of
20 pots (top schematization of Figure 1b). Each 20-pot set consisted of 10 pots filled with red soil and
10 pots filled with red soil (central schematization of Figure 1a). In turn, each subset of 10 samples was
subdivided in five pairs: a pre-established weight percentage of SAP (wSAP) was added to each pair of
samples, namely 0%, 0.2%, 0.5%, 1.0% and 1.5% of SAP. For each of these pair of samples, in one pot
the SAP was mixed with the surface/near-surface soil (psup); whereas in the other pot the SAP was mixed
deeper within the soil (pdeep), as depicted in the bottom schematization of Figure 1a.
The effect of SAP on the cultivations was then evaluated according to the following procedure.
Each sample was weighed before (i.e., in the dry state) and after watering with one liter of water.
Starting from the latter condition, the percentage water content (θs) of each sample was checked regularly
gravimetrically, and monitored over 78 days. During this period, further addition of water was performed
only when either of the following conditions occurred: