Erosion and tillage changes negatively the soil physical structure, which directly impacts agricultural systems and consequently food security. To mitigate these adverse modifications, different polymeric materials from synthetic and natural sources, have been used as soil conditioners to improve the hydro-mechanical behavior of affected soils. One of the most interesting and used natural polymers is the alginate hydrogel. Although commercially available alginate hydrogels are primarily sourced from algal, they can also be sourced from bacteria. The gelation capacity of these hydrogels is determined by their molecular properties, which, in turn, are influenced by the production conditions. Bacterial alginate hydrogel production offers the advantage of precise control over environmental conditions during cultivation and extraction, thereby maintaining and enhancing their molecular properties. This, in turn, results in higher molecular weight and improved gelation capacity. In this study, we compared the effects of bacterial alginate (BH) and algal alginate (AH) hydrogels over the mechanical, hydraulic, and structural behavior of coarse quartz sand as a model soil. Mechanically, it was observed that the treatment with the lowest concentration of bacteria alginate hydrogel (BH1) reached higher values of yield strength, Young’s modulus (E), shear modulus (G) and strain energy (U) than those treatments with algal alginate hydrogel (AH). Furthermore, the increase in the aggregate stability could be associated with the improvement of mechanical parameters. On the other hand, a greater water retention capacity was observed in the BH treatments, as well as a greater decrease in hydraulic conductivity with respect to the AH and control treatments. All these changes could be explained by the formation of bridge-like structures between the sand particles and the hydrogel, and this alteration may result in a shift in the mechanical and wettability characteristics of the treated soils. Finally, our findings emphasize the superior impact of bacterial alginate hydrogel on enhancing the mechanical and hydraulic properties of coarse quartz sand compared to traditional algal alginate. Besides, the use of bacterial alginate hydrogel could be useful to counteract erosion and water scarcity scenarios in agricultural systems.

Background/Objectives: The physiological disorder known as “orange spot” in Juglans regia L. cv. Chandler is an emerging kernel quality issue of increasing concern for the Chilean walnut industry. Characterized by a localized orange discoloration of the embryo, its etiology remains unknown. This study aimed to determine whether orange spot is associated with bacterial infection and to elucidate the metabolic alterations underlying its development, testing the hypothesis that it results from oxidative imbalance and lipid disorganization. Methods: Untargeted metabolomic profiling and fatty acid methyl ester (FAME) analysis were applied to compare affected (orange) and unaffected (white) walnut kernels collected from a commercial orchard in Melipilla, Chile, during the 2018 and 2022 seasons. Bacterial DNA was screened by PCR amplification of the 16S rRNA gene (799F/1193R). Results: Orange spot incidence reached 31–34% across seasons. No bacterial-sized amplicons were detected in either kernel type, indicating the absence of detectable bacterial DNA under the analyzed conditions. Metabolomic analyses revealed significant alterations in glyoxylate and dicarboxylate metabolism, glutamate-related pathways, and glycerophospholipid metabolism. Affected kernels exhibited reduced levels of L-glutamic acid and antioxidant-associated metabolites, alongside increased gluconic, citric and quinic acid, consistent with the redox imbalance and membrane oxidative degradation. FAME analysis showed higher total fatty acid content in affected kernels, suggesting intensified lipid turnover associated under oxidative stress. Conclusions: Orange spot is a physiological, non-infectious disorder linked to premature oxidative stress and lipid disorganization, negatively affecting walnut kernel quality.