*3.3. The Combination Variety-Rootstock Factor*

Regardless of the rootstock on which they were grafted, Marcona samples presented greater values of gross calorific value than Vayro samples. The rootstock that induced the highest calorific value in both cultivars was GF 305. As seen in Table 4 and Figure 3, the gross calorific value of Marcona on GF 305 is superior to Marcona on GF 677 and Marcona on GN Garnem respectively. This same pattern of behavior is repeated in Vayro variety. The highest carbon contents were found in the combination variety-rootstock Marcona-GF 305 (50.45%) followed by Marcona-GF 677 (48.80%), Marcona-GN Garnem (48.68%) and Vayro-GF 677 (48.73%). As shown in Table 3, which contains the Pearson correlation coefficients, the carbon content is much more influenced by the grafted variety than by the rootstock. All variety-rootstock combinations presented similar values on the hydrogen content except for Vayro-GF 305, which was lower. This result coincides with the one obtained in the individualized study of the rootstocks (Figure 2). The lowest nitrogen content was identified in the Vayro-GN Garnem combination.

**Table 4.** Influence of the interaction variety-rootstock factor in residual biomass characteristics (*n* = 108; mean value ± standard deviation; mean values with different minor letters (a–e) differ significantly).


In the same column, mean values with different minor letters differ significantly (*P* < 0.1).

**Figure 3.** Dispersion diagram for gross calorific values (J·g<sup>−</sup>1) according to the carbon and nitrogen content for each variety-rootstock combination.
