Hydrogel capsules as carriers for PGPB consortia enhance compost efficacy and nutrient uptake in Oat (Avena sativa) fertilization

Abstract Aims The incorporation of Plant Growth-Promoting Bacteria (PGPB) into compost is a promising strategy to enhance the potential of organic fertilizers. This study investigates in a pot experiment the potential of hydrogel capsules containing a PGPB consortium to improve compost efficiency, promote crop growth, and increase nutrient uptake. Methods Three PGPB strains ( Rhizobium leguminosarum T88, Herbaspirillum frisingense AP21, and Azospirillum brasilense D7) were encapsulated in hydrogel capsules made from amidated pectin via ionic gelation. Additives like skim milk, whey protein, and Gelita® EC were included. The capsules were characterized using scanning electron microscopy (SEM), moisture content analysis, and particle size measurement. Greenhouse experiments in pots assessed the impact of PGPB-enriched compost on oat growth ( Avena sativa var. Altoandina), nutrient uptake, and photosynthetic pigments. Results Encapsulated PGPB prototypes P1, P2, and P3 significantly increased shoot and root biomass, compared to the organic fertilization (O.F.) + 50% mineral fertilization (M.F.) treatment with P1 improving root biomass by 74%. In contrast, non-encapsulated treatments showed no significant effects. Encapsulated P1 and P2 enhanced root biomass by 48% and 39% compared to free-living cultures. Nutrient uptake, particularly of N, Ca, and Mg, improved with PGPB encapsulation, with P3 showing the highest increases, N by 81%, Ca by 66%, Mg by 77%. Photosynthetic pigments also rose, with chlorophyll-a increasing by 21% in P3, and chlorophyll-b by 58% in P2. Conclusions Encapsulated PGPB significantly enhances compost efficiency, boosting oat biomass, nutrient uptake, and photosynthetic pigment production, supporting sustainable agriculture.