## 1 Introduction  
Coarse-textured soils, characterized by a high proportion of sand and low organic matter content, often show loose structure, inadequate water retention capacity, rapid drainage, high susceptibility to accelerated nutrient leaching, and erosion vulnerability, which can limit their productivity and ecological resilience [1]. Defined by the Soil Science Glossary [2] as \"...any material such as lime, gypsum, sawdust, compost, animal manures, crop residue or synthetic soil conditioners that is worked into the soil or applied on the surface to enhance plant growth...\", soil amendments could enhance the physical, chemical, and biological properties of these soils, making them more suitable for productive use [3, 4]. The reason is that adding amendments to coarse soils can be expected to induce improvements in the bulk density [5], water retention [6], water use efficiency [7], aggregate stability [8], porosity [9], and hydraulic conductivity [10] of the soil. A recent trend envisions the transformation of organic waste into high-value soil organic amendments as a cornerstone of sustainable agricultural practices within the circular economy framework [11]. This shift aims to reduce environmental burdens associated with waste disposal while enhancing soil fertility, promoting carbon sequestration, and fostering microbial diversity, thereby contributing to long-term ecosystem resilience and agricultural productivity [1; 12]. Organic soil amendments refer to a wide variety of materials, including animal manure, crop residue, plant leaves, grass clippings, food processing by-products, and sewage sludge, all of which may arise as the residue or by-products of agricultural and industrial processes [13]. Compost, vermicompost, and biochar are organic amendments that can be expected to improve the physico-chemical properties of coarse soils [8; 14; 15]. For example, [PERSON] et al. [16] showed that a compost amendment increased the plant available water capacity (_PAWC_) of a sandy-loam, soil since organic matter incorporation primarily increased the micropore volume and decreased the macroporosity. Co-composted mixtures of maize, sewage sludge, and biochar significantly enhanced the water retention capacity of loamy sand soils, with the observed benefits being influenced by both the compost application rate and the specific type of feedstock used in the composting process [17]. The impact of compost and vermicompost amendments on the soil structure, water retention, and water use efficiency was investigated by [PERSON] et al. [10] on a sandy and a loamy soil. These authors found that these organic amendments enhanced the soil water-holding capacity, promoted macro-aggregate formation, and reduced bulk density, even when they were applied at low rates. Similar results were obtained by [PERSON] et al. [18], since the application of vermicompost to a sandy soil reduced bulk density, increased porosity, enhanced soil water and air permeability, and improved soil aggregation. [PERSON] et al. [19] evaluated the effects of biochar amendment on sandy-loam soils and they observed a significant promotion of macro-aggregate formation, an improvement in saturated soil hydraulic conductivity, an increase of saturated water content, and a decrease of residual water content. Biochar can also represent a sustainable approach to mitigate drought conditions and reduce the irrigation needs of desert sandy soils by improving soil porosity, water retention, aggregate stability, and plant-available water [20]. Despite the extensive literature on organic amendments, significant gaps remain in understanding how to optimize their use, warranting further investigation and more detailed studies. Exhaustive research on the effects of the applied rate of a given amendment and comparisons among different source materials are rare [21]. For example, to the best of our knowledge, no study has simultaneously considered and compared the effects of compost, vermicompost, and biochar on the physical quality of coarse-textured soils.