**3. Results and Discussion**

An overview of the chemical composition of almond tree biomass was conducted in order to describe the biomass potential of this species and how the selection of the vegetal material (variety and rootstock) and managemen<sup>t</sup> practices can influence the properties of the obtained biofuel.

Table 2 presents the values of proximate analysis, elemental composition and gross calorific value of the studied samples. All variables, except the percentage of hydrogen, present standard kurtosis and standard skewness between −2 and +2, ANOVA analysis can be performed, as they all follow normal distributions. The average gross calorific value obtained in our analysis shows similar results to those obtained in almond hulls and shells by Nhuchhen [44] or by Fernández-González [19] or Yin [26] for biomass. The results are also close to those found for other *Prunus* species, such as *Prunus Avium* L. [45] or *Prunus armeniaca* L. [46]. As can be observed, the concentrations of C and H were 48.11% and 5.77%, respectively, which are the same as those observed by Jenkins [47] for almond residues. Percentages of C, H, N are in the range of published data for other biomass groups (C = 42–71%; H = 3–11%; N = 0.1–12%) [48]. Low concentration of N, as is the case, is a positive characteristic, as high N produces a negative impact on the environment due to nitrogen dioxide emissions [19]. The greatest disadvantage of biomass when it is used as fuel is its high moisture content, which is inversely correlated with its calorific value [49]. Almond trees presented an average moisture content (8.40%) much lower than the average for woody species (20%) [50], which therefore makes it convenient for energetic uses.


The dependence of the studied variables is shown in Table 3. It has been proved in other studies that moisture content and percentages of C and H have a high influence on gross calorific value [45,51]. However, in our study, we observed that the variables that mostly influence the gross calorific value are not the composition of C, H, N, but variety, rootstock and, above all, variety-rootstock interaction. We found that the variable that influenced the percentage of N the most was the treatment applied. This result is consistent with other research [52,53] that concludes that fertilizers and pesticide doses are highly important for some elements, such as the nitrogen content.

Given the obtained results, a variance analysis was carried out in order to compare the influence of the different factors analyzed in this study.


