###### Abstract  
Soil salinization and desertification due to climate change are the most relevant challenges for the agriculture of the 21 st 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 quinao), 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 \({}^{\circ}\)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. s 2021 2 February 2021 24 February 2021 24 February 2021 27 February 2021 2  
of this resource not only leads to its depletion, but also to another relevant problem: the salinization of soils [1]. All soils contain salt and nutrients whose quantity depends on the pedo-climatic conditions of the territory [2], but when their amount exceeds the critical threshold crops are negatively affected and the soil is classified as saline. Salinization is a process typical of environments where rainfall is not sufficient to eliminate salts contained in the soil determining their increase [3]. It is estimated that worldwide about 20% of total cultivated lands and 33% of irrigated agricultural lands are afflicted by high salinity, and, moreover, 50% of the arable lands will be affected by high level of salts by 2050 [4]. Salinization inhibits plant growth since it limits their ability to supply water, causes nutritional imbalances and induces toxicity phenomena [5]. Saline soils can be classified into three classes based on salinity and sodium values, estimated by electrical conductivity (EC) and sodium adsorption ratio (SAR) or exchangeable sodium percentage (ESP): saline, saline- sodium and sodium. Soil is defined as saline when the EC is slightly greater than 4 deci-Siemens per meter (dS m\({}^{-1}\)), mild between 4 and 8 dS m\({}^{-1}\), moderate between 8 and 16 dS m\({}^{-1}\), and high above 16 dS m\({}^{-1}\)[6]. Values above 4-8 dS m\({}^{-1}\) reduce the growth of many crops except for halophytes (i.e., plants that tolerate or live on soils rich in salts) and only a few cultivated species have a high tolerance to salinity (e.g., beet). To solve the problem of soil salinization, several agronomic techniques can be adopted such as: reducing the excess of water that infiltrates the soil, the use of crop mutants, organic amendments, but also of microorganisms tolerating salinity [7]. Organic fertilizers intended also as soil amendments such as high-quality compost, obtained from the differentiated waste collection, or biochar, produced by means of pyrolysis processes, are able to promote soil health and stability, and reduce, in some cases, human health risks [8].