Enhancing faba bean (Vicia faba L.) productivity and improving soil fertility using organic amendments in alkaline soil

The present investigation aimed to evaluate the effectiveness of various organic soil amendments in promoting the growth and productivity of faba beans (Vicia faba L.) grown in alkaline soil conditions. Eleven treatments were applied on a new faba bean cultivar called Sakha 5 with four separate replicates by using a completely randomized (CRD) experimental design, under a greenhouse pot experiment condition at the Experimental Farm of Sakha Agricultural Research Station, Kafr El-Sheikh, Egypt, during two consecutive seasons from 2021/22 to 2022/23. The amendments included rice husk biochar (RHB), wood vinegar (WV), biogas digested residues (BDR), and molasses (M), applied individually and in six pairwise combinations (WV + RHB, WV + BDR, WV + M, RHB + BDR, RHB + M, and BDR + M). All pots received basal mineral fertilization as calcium superphosphate (to supply 60 g P pot⁻¹), potassium sulfate (to supply 15 g K pot⁻¹), and ammonium nitrate (as an N source, applied in split doses). The data obtained indicated that all soil amendment treatments significantly improved plant growth, seed yield, and protein content in comparison to the unaltered control. Among all treatments, WV + RHB showed the strongest response, raising chlorophyll to 48 and 55 SPAD (control: 42 and 46; ~14–20% increase), root dry weight to 9.67 and 8.30 g plant⁻¹ (control: 5.33 and 3.00; ~56–177% increase), root volume to 10.0 and 13.0 cm³ plant⁻¹ (control: 6.33 and 6.20; ~58–106% increase), and nodulation to 67 and 65 nodules plant⁻¹ (control: 30; ~117–123% increase), while also achieving the highest nutrient uptake (N 3.98–3.68, P 42.10–42.30, K 2.58–2.55 g plant⁻¹; Fe 14.00–14.48, Mn 2.96–2.50, Zn 2.30–2.70 g plant⁻¹) and the maximum seed yield (≈ 37 g pot⁻¹). In conclusion, this research demonstrates that the simultaneous use of rice husk biochar and wood vinegar constitutes a successful and sustainable strategy for improving the productivity of alkaline soils, offering a promising, eco-friendly approach to enhance faba bean crop performance.