Soil amendments and microbial inoculants can affect plant growth, water retention, and crop resilience. This study investigated the effects of two amendments, extracellular polymeric substances (EPS) and biochar, with and without bacterial inoculation, on maize (Zea mays) growth, irrigation needs, and physiological responses. Maize was cultivated in soil with 2.5 % and 5 % (w/w) of wet EPS (Kaumera®) or biochar and inoculated with a bacterial consortium consisting of Arthrobacter nicotinovorans EAPPA and Rhodococcus sp. EC35.

EPS-treated plants exhibited significantly higher shoot biomass, larger stem thickness, while soil plant analysis development (SPAD) values suggest improved nutrient availability and photosynthetic efficiency. In non-inoculated plants, EPS supplementation increased shoot dry biomass by 78 % and stem thickness by 9 % compared to control plants grown without amendments. This enhancement strongly correlated with nutrient uptake, especially in plants supplemented with 5 % of EPS. Particularly, Mg and Ca concentrations increased by 195 % and 73 %, respectively, compared to non-amended controls. Inoculation further amplified these benefits, underscoring its key role in plant development and resilience. In contrast, biochar-treated plants exhibited reduced growth, suggesting stress effects at the tested addition doses. Electrolyte leakage, a key indicator of plant stress, was significantly lower in soils amended with EPS, suggesting that EPS provides a protective effect to the plants. EPS also demonstrated remarkable water retention benefits, reducing irrigation requirements by 30 % with 5 % of EPS application, compared to 9 % reduction with biochar. The use of EPS, combined with microbial inoculants, represents a sustainable agricultural strategy for optimizing maize production in water-limited environments.

Extracellular polymeric substances (EPS) recovered from aerobic granular sludge (AGS) produced in wastewater treatment plants (WWTP) offer valuable biomaterials with multiple applications, including in agriculture. This study evaluated the potential of EPS derived from AGS collected from two full-scale WWTP in Utrecht (EPS_U) and Faro (EPS_F) and one laboratory-scale reactor (EPS_R), as soil amendments. A 49-day greenhouse experiment assessed the effects of two wet EPS doses (0.5% and 1% w/w) on maize (Zea mays L.) growth, nutrient uptake and use efficiency, and soil enzymatic activities. EPS amendments were compared to vermicompost at equivalent doses and a non-amended control. Overall, EPS outperformed vermicompost amendments, although the source and dose greatly influenced their performance. Notably, applying 1% of EPS, regardless of the source, consistently increased maize chlorophyll content, with EPS_R_1% increasing it by 62% and 105% compared to 1% vermicompost and the control, respectively. The EPS doses applied had a marginal influence on biometric traits, but 1% of EPS_R significantly increased shoot fresh weight and thickness. Magnesium and potassium contents in shoots increased by 46% and 34% in EPS_R_1% and EPS_F_1% amendments, respectively, over the control. The soil enzyme activities differed across EPS amendments, with soils containing EPS_U_1% showing higher urease (+ 41%) and fluorescein diacetate hydrolysis (+ 31%) activities, whereas EPS_R_1% stimulated acid phosphatase (+ 35%) activity, demonstrating EPS contribution to microbial activity and nutrient cycling in the rhizosphere. EPS amendments have great agronomic potential, providing superior benefits to vermicompost while supporting waste sludge valorization and embracing sustainable agriculture practices.