# Evaluation of Conifer Wood Biochar as Growing Media Component for Citrus Nursery
## 3 Results and Discussions
### Evolution of Plant Growth  
The seedlings height was significantly greater for G (control) than for B (Figure 1A). This agrees with previous results which report maximum growth and stem diameter for citrus seedlings in media containing a lower amount of peat (peat + sand 1:4) [51]. At the end of the trial, the grafted plants all reached similar heights (Figure 1A). The values of stem diameter were significantly greater in C than in B, E, and F. Seedlings cultivated in all biochar growing media were similar to control G (Figure 1B). In the grafted plants, stem diameter was greater in growing media C than in F. Also, seedlings in growing media containing biochar were comparable to G (Figure 1B). The destructive analyses (Figure 2) during winter for all growing media show that the dry matter accumulated in leaves, stems, and taproots were similar for all mixtures. The differences did occur in root systems development. The highest dry matter accumulation was shown in A, with accumulation in B, C, D, and E being significantly lower. The root system in A and G growing media represented  
Figure 1: (**A**) Seedling height and (**B**) stem diameter at soil level measured on rootstocks in various growing media just before grafting and five months after grafting. For each parameter and period ANOVA and mean separation by [PERSON]’s HSD test (\(p\leq 0.01\); bars represent standard deviation). \({}^{\mathrm{a}}\) Growing media was 50% sandy soil + 50% of the following: A = black peat and perlite 1:1; B = biochar 1; C = black peat, perlite, and biochar 0.5:10.5; D = black peat and biochar 1:1; E = black peat, compost, and biochar 0.5:0.5:1; F = black peat, perlite, compost, and biochar 0.5:0.5:0.5:0.5; G = black peat and lapillus 1:1 (control, mixture adopted by the hosting nursery). 20% of the total dry weight; whereas in the biochar growing media, except for F, the root systems accounted for 11% (B), 10% (C), 10.19% (D), and 13% (E) of total dry weight. These values do not completely agree with the findings of [PERSON] and colleagues [52] who found higher values of dry weights for one-year-old roots of Pera sweet orange tree grafted on Rangpur lime grown in commercial inert substrates. Therefore, the substrate and the slow-release fertilization did not affect the seedlings' growth rate. In spring, there were no significant differences between growing media for dry matter content of leaves and stems. However, the roots of A and G (control) differed significantly from D. The taproot dry matter in B was significantly lower than in A and G at the end of the trial. In spring, A, F, and G (control) showed a drastic reduction in root dry matter (13.62%, 12.91%, and 14.49%, respectively), while the other growing media showed a slight increase (Figure 2). In spring, the root/stem ratio ranged from 0.18 for D to 0.25 for G. The root dry mass reduction in spring was is in line with the findings of [PERSON] and [PERSON] [53] who reported that in citrus trees, and in Carrizo citrange in particular, even in non-limiting soil and climatic conditions, roots' growth rate decreased during the period when shoot growth was particularly rapid. Therefore, root dry matter content reductions in spring in G (control), A, and F, were probably due to a greater degradation of secondary roots and hairs between winter and spring resulting in alternating patterns of root and shoot growth. The lower root growth than aerial growth indicates an acceptable root system efficacy. However, the significant low root growth within the deepest layers of the pot could be caused by the reduction of substrate quality. As observed, this is due to the collection of small particles in the ground level of the pot thus reducing the porosity (not shown). With an increase in bulk density, the macroporosity is decreased,  
Figure 2: Dry matter distribution recorded in winter (February 2015) and spring (April 2015) of Carrizo citrange seedlings potted in different growing media.