The Development and Condition of Selected Legume Species Depending on the Rate of Superabsorbent Application Under Conditions of Limited Irrigation

The aim of the study was to assess the effect of superabsorbents on the condition of selected legume species grown with different watering frequencies. Three two-factor pot experiments were conducted in MICRO-CLIMA phytotrons. The objects of the study were three legume species: faba bean, pea and soybean. The first factor was the superabsorbent (SAP) rate (0, 2, 4, and 6 g·kg−1 of substrate), while the second factor was the watering frequency (the subjects were watered every 1, 3, 6, and 9 days). The study showed that faba bean and pea plants were significantly taller after superabsorbent application (by 17 and 11%, respectively) and developed greater root mass. The application of SAPs at a rate of 6 g·kg−1 increased the dry weight of the underground parts of faba beans and peas (by 56.8% and 85.9%, respectively) compared to the control. The highest SAP dose reduced the Fv/Fm index in soybean and the PI index in faba bean and soybean (by 5 and 29%, respectively). The lowest SPAD index in peas was recorded in the control treatment (without SAPs) and in soybeans at the highest dose of SAPs (6 g·kg−1). In all species, the best results for growth and biomass of the aboveground parts were obtained with daily watering, which increased plant height by an average of 26.5–60.9% and the dry mass of the aboveground parts by 42.6–60.6% compared to less frequent watering. Higher values of the Fv/Fm index were observed in soybean, and higher values of the PI index were observed in faba bean, pea, and soybean in the least frequently watered treatments. In all species studied, the SPAD index was higher under conditions of the greatest water deficit (watering every 9 days) compared to plants watered every 1, 3, and 6 days.