Effects of Polymer Application Rates on Yield and Photosynthesis in Faba Bean and Pea

Climate change exacerbates soil moisture deficits, necessitating efficient water retention strategies. Superabsorbent polymers (SAPs) offer a potential solution to enhance water availability for crops during dry periods. Faba bean (Vicia faba L.) and pea (Pisum sativum L.) were selected as model legumes due to their high nutritional value, agricultural importance in temperate regions, and sensitivity to drought stress This study evaluated the effects of different SAP application rates on the yield and physiological performance of two legume species: faba bean (cv. Granit) and pea (cv. Batuta). The two-year (2017–2018) field experiments employed a randomized block design with four replicates. Treatments included three SAP doses: 0 (control, SAP0), 20 (SAP20) and 30 (SAP30) kg·ha−1. The study was conducted over two years with contrasting weather: 2017 was wetter but had uneven rainfall distribution, while 2018 was drier and characterized by moisture deficits during critical growth stages. SAP application significantly increased seed yield in faba bean and pea, with the most favorable effect observed at 20 kg ha (average yield increase of 23.6% and 17.3%, respectively). SAP did not affect yield components in faba bean. However, in peas, an increase in pod number and seed number per plant was observed with the SAP30 dose compared to the SAP20 dose. Application of superabsorbent at a dose of 20 kg ha−1 significantly increased photosynthesis rate in faba bean, the Fv/Fm index in the tested species, and the PI in peas compared to the control. However, the superabsorbent did not affect transpiration rate or the WUE coefficient in the tested legume species. Significantly higher yields in faba bean and pea and all tested plant structure parameters in pea were recorded in 2018 compared to 2017. The tested parameters of gas exchange and chlorophyll fluorescence were higher in pea in 2018 (except for transpiration intensity) and in faba bean in 2017. The findings suggest that SAPs can be a useful tool to mitigate water stress effects in legumes, although their effectiveness depends on environmental conditions. Therefore, SAP application may be a promising agronomic strategy in regions prone to irregular rainfall or moderate drought.