Morphological features of perennial legumes root systems in the context of their agroecological impact on soil

The morphological and quantitative features of the underground architectonics of six perennial legume species (Medicago sativa L., Trifolium pratense L., Onobrychis arenaria Kit., Melilotus albus Medik., Lotus corniculatus L., Galega orientalis Lam.) were investigated during the first two years of the growing season, and their direct impact on the ecological and agrochemical parameters of grey forest soil in the Ukrainian forest-steppe was evaluated. It was established that during the second year of vegetation, a rapid multiplicative increase in individual linear plant parameters occurs; Melilotus albus (260 cm) and Medicago sativa (258 cm) lead in taproot penetration depth, while Lotus corniculatus leads in the accumulation of regeneration buds (51 units). It was found that from a coenotic perspective, the peak agroecological effect per hectare occurs specifically during the second year of vegetation. During this period, Galega orientalis forms a record fresh biomass of underground organs (322.40 t/ha), ensuring the highest rates of humus accumulation in the soil (up to 2.05% compared to the baseline 2.0%). The study proved the existence of clear functional links between the architecture of the underground sphere of grasses and the transformation of nutrients: The deep branching and thick central root of Onobrychis arenaria (7 mm) maximize the content of available phosphorus (413 mg/kg) and potassium (84 mg/kg), while the powerful lateral roots of Melilotus albus (3.0 mm) stimulate calcium accumulation (135 mg/kg). Two-year cultivation of legumes optimizes soil acidity, reducing hydrolytic acidity by 24.5-28.3% and shifting the pH toward neutral values (7.2-7.3). The results reveal the phytomorphological mechanisms of fertility restoration and the improvement of the soil chemical profile in agroecosystems.