Lettuce seedlings often require the use of fertilizers for their cultivation management to achieve appropriate yield. However, for eco-sustainable chemical-fertilizers-free agronomy, the implementation of totally organic farming often cannot support lettuce productivity, therefore new natural biostimulants able to increase lettuce yield could be considered of great interest. In this preliminary work, the foliar spray application of a Chlorella vulgaris extract in lettuce seedlings was investigated in order to achieve better yield performance. Its biostimulant effect was evaluated by monitoring the morphobiometric parameters, chlorophylls, carotenoids, total protein contents, and several enzymatic activities involved in primary and secondary metabolisms of the plant. The experimental trials were carried out by growing lettuce seedlings on inert substrate (pumice) with a 16 h photoperiod for 21 days. The treatment consisted of three consecutive applications by foliar spraying using a concentration of the C. vulgaris extract, corresponding to 1 mg C_org L⁻¹, which were performed one week apart. The results showed that the C. vulgaris extract positively influenced the growth of lettuce seedlings, by increasing the fresh and dry weights, chlorophylls, carotenoids, protein content, and ashes at shoot level. From a biochemical point of view, primary and secondary metabolisms of shoots, in particular nitrogen metabolism, were positively influenced. At the root level, the extract increased dry matter, proteins, and ash content.

The pollution of water caused by the excessive presence of organic and inorganic compounds, such as nitrates, phosphates, heavy metals, antibiotics, agrochemicals, etc., is one of the major environmental problems in many countries. Various approaches to remediate wastewater are available, and this review mainly provides the state of the art about the possible adoption of microalgae-based treatments (phycoremediation), which may represent a good alternative to conventional purification methods. Because of its composition, wastewater can provide several nutritional compounds (e.g., carbon, nitrogen, and phosphorus), which represent the essential nutrients for microalgae growth. Microalgae are also attracting the interest of worldwide researchers due to their multipurpose applications; in particular, microalgae cells can represent a useful feedstock for various sectors, among these, the agricultural sector. This review proposes a detailed description of the possible application of microalgae in the process of remediation of wastewaters of different sources, highlighting their possible advantages. Moreover, the review aims to report the application of the microalgae biomasses and their extracts in agriculture, as microalgae-based products can represent a valid alternative to traditional agrochemicals, offering sustainable solutions to improve agricultural technologies. Therefore, since the recently developed wastewater depuration technology based on phycoremediation may directly provide valuable microalgae biomasses, it can be used as a powerful starting means to produce agricultural products able to improve yield and quality of crops (biostimulants, biofertilizers), as well as induce pest and disease resistance (biopesticides).

Climate change has reshaped global weather patterns and intensified extreme events, with drought and soil salinity negatively impacting the yield and quality of crop production. To mitigate the detrimental effects of drought stress, the introduction of beneficial plant growth-promoting rhizobacteria (PGPR) has proven to be a promising approach. In this study, we evaluated a synthetic microbial community (SynCom) comprising bacterial strains belonging to the species Bacillus velezensis, Pseudomonas simiae, P. salmasensis, Glutamicibacter halophytocola, and Leclercia sp., which have been demonstrated to promote tomato growth both individually and collectively. The SynCom and most of its individual bacterial strains were shown to mitigate the detrimental effects of polyethylene glycol (PEG)-induced drought stress in vitro in Arabidopsis thaliana seedlings, either by reducing alterations in xylem elements or promoting the formation of new xylem strands. In a greenhouse trial, soil drenching with the SynCom and two individual strains, B. velezensis PSE31B and P. salmasensis POE54, improved the water stress response in soilless-grown tomato plants under a 40% reduced irrigation regime. Additionally, bacterial treatments positively influenced the diversity of rhizosphere bacterial communities, with distinct changes in bacterial composition, which suggest a treatment-specific interplay between the introduced strains and the native microbiome. These findings highlight the potential of microbial consortia and individual PGPR strains as sustainable tools to improve plant resilience to abiotic stresses.

The cultivation of microalgae using urban wastewater as a nutrient substrate represents a promising bio-refinery concept that can serve multiple purposes; indeed, it allows for the generation of biomass, which can be used for various applications while meanwhile removing nutrients from wastewater. In this study, the potential of urban wastewater collected at two different time periods in a farmhouse as a nutrient substrate for microalgal growth was assessed. Wastewater samples were treated on a laboratory scale, inoculating reactors with two common species, Chlorella vulgaris (CV) and Scenedesmus quadricauda (SQ), and with an autochthonous strain of Klebsormidium sp. K39 (Kleb), directly isolated from effluents of the same system. The main aim of the study was to compare the microalgae’s performances in terms of wastewater re-mediation and biomass productivity. In the first case study, which involved an effluent with a lower pollutant level, microalgal cultivation showed removal efficiencies in the range of 57–63% for total nitrogen, 65–92% for total phosphorous, 94–95% for COD, and 100% for E. coli. In the second case study, involving an effluent with a higher pollutant level, the remediation performances of the three microalgae strains ranged from 93 to 96% for total nitrogen, from 62 to 74% for total phosphorous, from 96 to 97% for COD, and 100% for E. coli. At the end of the experimental trials, treated waters showed values of pollutants suitable for irrigation use, in accordance with environmental and national legislation, which established specific thresholds for irrigation purposes.

Municipal waste biomass could be valorized as an alternative feedstock to produce compounds beneficial for agricultural applications. The foliar spray application of biostimulants emerges as a promising and innovative technique due to its environmental safety and ability to enhance crop yields. In recent years, the exploitation of biopolymers obtained through alkaline hydrolysis of the solid anaerobic digestate from municipal biowastes has attracted researchers’ interest. The aim of this study is to investigate the effects on lettuce growth of a product obtained through alkaline hydrolysis from municipal biowaste, Biopolymers (BPs), and of a derivate subjected to a further oxidation process, Biopolymers Oxidate (BPs OX). The effects of the treatments at various concentrations were evaluated by monitoring plant growth and observing the trends in the activities of the main enzymes involved in the nitrogen metabolic pathway of lettuce. Results suggest that the best treatments in terms of fresh weight were achieved by using BPs at 10 mg/L and BPs OX at 100 mg/L, increasing yield by around 28% and 34%, respectively. The innovative aspect of this work was to make easier for farmers the biopolymers application by testing a foliar spray methodology for BPs and BPs OX, which has never been tested before in any crop.

This study investigates bio-acidification as a method to decrease the pH of animal manure in dairy farms through the application of coffee silverskin (i.e., a coffee torrefaction waste) and acetic acid. The aim was to focus on the preliminary analysis needed to assess the suitability of using this mitigation strategy. This analysis was carried out by developing a three-step methodology. The first step included the identification of the appropriate proportions of coffee silverskin and acetic acid at the laboratory scale; in the second step, the best treated proportions were analysed in field conditions to compare the statistical differences among the pH of the control and treated samples. In the third step, territorial evaluation was carried out to verify the availability of the coffee waste in the territory based on the use of a Geographic Information System (GIS). Based on the results, a reduction of 38% and 31% in pH was observed in samples treated with acetic acid and coffee silverskin at the laboratory scale and in field conditions, respectively. The territorial analysis showed that it is possible to valorise this agro-industrial waste while minimising environmental impacts due to transportation if the coffee industry is located within a 75 km distance.