Nutrients and non-essential elements in edible crops following long-term mineral and compost fertilization of a Mediterranean agricultural soil

Counteracting action of Bacillus stratosphericus and Staphylococcus succinus strains against deleterious salt effects on Zea mays L

The salinization of soil is the process of progressive accumulation of salts such as sulfates, sodium, or chlorides into the soil. The increased level of salt has significant effects on glycophyte plants, such as rice, maize, and wheat, which are staple foods for the world's population. Consequently, it is important to develop biotechnologies that improve crops and clean up the soil. Among other remediation methods, there is an environmentally friendly approach to ameliorate the cultivation of glycophyte plants in saline soil, namely, the use of microorganisms tolerant to salt with growth-promoting features. Plant growth-promoting rhizobacteria (PGPR) can improve plant growth by colonizing their roots and playing a vital role in helping plants to establish and grow in nutrient-deficient conditions. Our research aimed to test in vivo halotolerant PGPR, isolated and characterized in vitro in a previous study conducted in our laboratory, inoculating them on maize seedlings to improve their growth in the presence of sodium chloride. The bacterial inoculation was performed using the seed-coating method, and the produced effects were evaluated by morphometric analysis, quantization of ion contents (sodium, potassium), produced biomass, both for epigeal (shoot) and hypogeal (root) organs, and by measuring salt-induced oxidative damage. The results showed an increase in biomass and sodium tolerance and even a reduction of oxidative stress in seedlings pretreated with a PGPR bacterial consortium (Staphylococcus succinus + Bacillus stratosphericus) over the control. Moreover, we observed that salt reduces growth and alters root system traits of maize seedlings, while bacterial treatment improves plant growth and partially restores the root architecture system in saline stress conditions. Therefore, the PGPR seed-coating or seedling treatment could be an effective strategy to enhance sustainable agriculture in saline soils due to the protection of the plants from their inhibitory effect.

Metagenomic Analysis of Bacterial Community Structure and Dynamics of a Digestate and a More Stabilized Digestate-Derived Compost from Agricultural Waste

Recycling of different products and waste materials plays a crucial role in circular economy, where the anaerobic digestion (AD) constitutes an important pillar since it reuses nutrients in the form of organic fertilizers. Knowledge about the digestate and compost microbial community structure and its variations over time is important. The aim of the current study was to investigate the microbiome of a slurry cow digestate produced on a farm (ADG) and of a more stabilized digestate-derived compost (DdC) in order to ascertain their potential uses as organic amendments in agriculture. The results from this study, based on a partial fragment of 16S bacterial rRNA NGS sequencing, showed that there is a greater microbial diversity in the DdC originated from agricultural waste compared to the ADG. Overall, the existence of a higher microbial diversity in the DdC was confirmed by an elevated number (1115) of OTUs identified, compared with the ADG (494 OTUs identified). In the DdC, 74 bacterial orders and 125 families were identified, whereas 27 bacterial orders and 54 families were identified in the ADG. Shannon diversity and Chao1 richness indexes were higher in DdC samples compared to ADG ones (Shannon: 3.014 and 1.573, Chao1: 68 and 24.75; p < 0.001 in both cases). A possible association between the microbiome composition at different stages of composting process and the role that these microorganisms may have on the quality of the compost-like substrate and its future uses is also discussed.

Influence of the Choice of Cultivar and Soil Fertilization on PTE Concentrations in Lactuca sativa L. in the Framework of the Regenerative Agriculture Revolution

Evaluating the relative weight of the choice of cultivar and soil fertilization on potentially toxic elements (PTEs) accumulation is crucial in promoting informed decisions in the framework of regenerative agriculture. To this end, 11 PTEs (Cd, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, Zn) were determined in both leaves and roots of six cultivars (Stylist, Xanadu, Aljeva, Bacio, Analena, Vincenzo) of lettuce (Lactuca sativa L.) grown side by side on mineral fertilized or biowaste compost amended soils, under greenhouse conditions. The use of multivariate and linear modelling approaches indicated that the organ and cultivar primarily account for the variability in PTE concentrations. In terms of PTE partitioning between organs, Cd and Mg were preferentially accumulated in leaves, whereas Cu, Pb, K and Zn in roots. As for the cultivar, Xanadu showed the highest concentrations of several PTEs, with Cd reaching concerning levels. Fertilization had a detectable contribution only on Cd accumulation, slightly increased in leaves by compost. Findings highlight the key role of cultivar choice in guaranteeing food safety and grant the possibility to adopt biowaste compost in regenerative agriculture without concerns about PTE accumulation enhancements in lettuce, but demand a cautionary approach in the case of Cd.

Reference intervals for trace elements in the general Danish population and their dependence on serum proteins

Reference intervals that indicate the anticipated results of clinical chemistry parameters in a healthy background population are essential for the proper interpretation of laboratory data. In the present study, we analysed major trace elements in blood samples from 400 randomly selected members of the general Danish population. Reference intervals were established for trace elements in both whole blood and serum, and associations with major plasma transport proteins were investigated. In the case of a statistically significant correlation, a corresponding protein-adjusted reference interval was established for comparison with the unadjusted interval. While several trace elements correlated with albumin, ferritin and transferrin, the overall impact of transport proteins was minor and resulted in only marginal changes in the reference intervals. In conclusion, the updated reference intervals for trace elements can be employed without adjusting for plasma protein concentrations.

Effects of Compost Amendment on Glycophyte and Halophyte Crops Grown on Saline Soils: Isolation and Characterization of Rhizobacteria with Plant Growth Promoting Features and High Salt Resistance

Soil salinization and desertification due to climate change are the most relevant challenges for the agriculture of the 21st century. Soil compost amendment and plant growth promoting rhizobacteria (PGP-R) are valuable tools to mitigate salinization and desertification impacts on agricultural soils. Selection of novel halo/thermo-tolerant bacteria from the rhizosphere of glicophytes and halophytes, grown on soil compost amended and watered with 150/300 mM NaCl, was the main objective of our study. Beneficial effects on the biomass, well-being and resilience, exerted on the assayed crops (maize, tomato, sunflower and quinoa), were clearly observable when soils were amended with 20% compost despite the very high soil electric conductivity (EC). Soil compost amendment not only was able to increase crop growth and biomass, but also their resilience to the stress caused by very high soil EC (up to 20 dS m−1). Moreover, compost amendment has proved itself a valuable source of highly halo-(4.0 M NaCl)/thermo tolerant rhizobacteria (55 °C), showing typical PGP features. Among the 13 rhizobacterial isolates, molecularly and biochemically characterized, two bacterial strains showed several biochemical PGP features. The use of compost is growing all around the world reducing considerably for farmers soil fertilization costs. In fact, only in Italy its utilization has ensured, in the last years, a saving of 650 million euro for the farmers, without taking into account the environment and human health benefits. Furthermore, the isolation of halo/thermo-tolerant PGPR strains and their use will allow the recovery and cultivation of hundreds of thousands of hectares of saline and arid soils now unproductive, making agriculture more respectful of agro-ecosystems also in view of upcoming climate change.

Compost and Sewage Sludge for the Improvement of Soil Chemical and Biological Quality of Mediterranean Agroecosystems

Conventional fertilization practices in agroecosystems concern the supply of bioavailable nutrients, such as mineral fertilizers. A consolidated alternative to restoring the long-term fertility of agricultural soils is their amendment with organic fertilizers. Soil amendment with biowaste compost or sewage sludge represents a sustainable strategy to avoid the landfilling of organic matter derived from urban waste and sewage sludge. This study aims at validating the use of quality biowaste compost and sewage sludge from secondary sedimentation (alone or in combination with mineral fertilizers) in a Mediterranean agroecosystem and their effects on soil chemical and biological quality, with a view to verifying the maintenance of soil fertility and functionality. In particular, the dynamics of soil organic matter, pH, potentially toxic elements and microbial community functionality were assessed, in experimental mesocosms, during 6 months of incubation. The research showed that, while soil amendment with biowaste compost induces positive effects on soil organic matter and phosphorous concentrations, as well as on microbial community functionality, the amendment with the selected sewage sludge does not determine any benefit to the microbial community or any danger in relation to soil potentially toxic element concentrations and toxicity. The quantity of sewage sludge employed, chosen according to regional directives, was thus not enough to stimulate the edaphic microflora activity.

Agricultural waste

The management of agricultural waste has become very important because the inappropriate disposal yields negative effects on the environment. The resource recovery from agricultural waste which converts waste into available resources can reduce the waste and new resource consumption. This review summarizes the 2018 researches of over three hundred scholar papers from several aspects: agricultural waste, and, waste chemical characterization, agricultural waste material, adsorption, waste energy, composting, waste biogas, agricultural waste management, and others.