3.2. Root system morphology characteristics
Most of the root morphometric parameters were strongly determined by the soil depth (Figure 2). The highest root biomass was characterized for the upper soil layer (0‑5 cm), representing 54% of RDMD for the whole investigated soil layer. The RDMD percentages for the deeper soil layers, 5‑10, 10‑15 and 15‑20 cm, were 19, 14 and 13%, respectively. Similar proportions were calculated for the RLD parameters, at 57, 19, 12 and 12%, respectively. The most numerous RLD diameter fractions were 0.002-0.005 mm, with 43% of the total RLD value (Figure 3). The root diameter fraction in the range of 0.1-0.2 mm was also characterized by a high share (20.1%) of the root biomass. The effect of the different soil amendment applications on the RLD values was observed for all diameter fractions in equal proportions.
The MRD was not significantly affected by the soil depth. The MRD in the particular soil layers varied from 0.0770‑0.0837 mm. The treatments used changed some of the root morphometric parameters, i.e., the RLD, MRD, RSA and RSR (Table 5). The RDMD, RVD and SRL were not significantly different for any treatments used in this trial. The CTR was characterized by the lowest RLD value (16.9 cm cm-3). Straw and biochar application resulted in higher RLDs, with the highest value for WBL (34.7 cm cm-3). A similar relationship was observed for the RSA. The lowest value was calculated for the CTR (0.382 cm2 cm-3) and the highest for WBL (0.838 cm2 cm-3). Organic amendment resulted in higher MRDs. The CTR and MCTR were characterized by low MRDs below 0.08 mm, but MRD was at the same level with WS. The MRD increased when straw or biochar were applied, with the highest root diameter (0.0904 mm) with MBL. Whether there was a relationship between the root morphometric parameters and the aboveground shoot biomass was assessed. Only the MRD was correlated with plant yield (Table 6). However, Pearson’s correlation coefficient was significant only for the 1st cut (Figure 4).
The RSR was found to be a more sensitive root morphometric parameter. The RSR was affected not only by the soil depth but also by the treatments used in this trial. Low values of the RSR, which were below 0.7, were observed for the CTR, MS and WS treatments. When biochar was applied, the RSR increased to values above 0.7. The RSR was at a similar level with the MCTR treatment (0.842). A higher RSR was obtained for the treatments with biochar applied at a higher rate (5 t ha-1) than for treatments with biochar applied at a lower rate (2.25 t ha-1).
The differences for most of the root morphometric parameters were noticed mainly between the CTR, without any amendments, and other treatments where straw or biochar produced from miscanthus or wheat were applied. However, there were no differences between the feedstock type (miscanthus vs. wheat), materials (straw vs. biochar) or amendment rates (5 vs. 2.25 t ha-1).