Since the addition of biochar had modified the water retention
characteristics of the soil under investigation, it was expected that
it might also affect the crop yields of durum wheat. In order to
verify this hypothesis, we estimated the impact of the biochar
addition on the simulated crop yield (CY), drainage (DR), water
content (SWC) and plant extractable water (PEW) of the soil, using
as data inputs the physical properties of the soil obtained from the
C0, C10 and C30 treatments in a similar way to the method used in
the sensitivity analysis. To run DSSAT, we used a dataset of inputs,
including weather, soil properties and plant parameters. To be
more precise, weather data (solar radiation, rainfall and temperatures)
recorded at the weather station of the Experimental Farm
of Foggia (between 1951 and 2013) in ten randomly selected years
(i.e., those with annual rainfall higher than 50% of the cumulative
empirical frequency distribution) were used to simulate the
cultivation of durum wheat. The DSSAT model had been previously
calibrated and validated in the test area for winter durum wheat
(Rinaldi, 2001), and then successfully applied in assessments
which mainly focused on the impact of climate change on crop
rotation (Ventrella et al., 2012a,b). The agricultural years when
drainage was zero were discarded. The soil properties that are
measured and calibrated and used in this analysis, as well as the
assumed data on the soil profile under free drainage, are
summarized in Table 4. Thus the variables under consideration
represent the simulated mean values for the whole crop season
between September and May for each of the considered years of
weather data.