Healthy soils are fundamental to agriculture, supporting food security and environmental health. They play a key role in carbon storage, water regulation, and biodiversity preservation, making them vital allies in combating climate change. Assessing soil health involves examining properties like texture, structure, consistence, and nutrient levels. This analysis is crucial for understanding ecosystem status and guiding agricultural practices.

Improving soil health is essential for reducing greenhouse gas emissions and enhancing carbon sequestration, which increase resilience to climate change. FENIX project focuses on developing soil improver products designed to rejuvenate soil health. These products aim to improve soil structure and fertility and boost water retention, addressing climate change and drought challenges. By offering cost-effective solutions that reduce the need for chemical fertilizers, these soil improvers support a transition to eco-friendly farming, promoting long-term sustainability and profitability.

Biochar, a charcoal derived from pyrolysis, a renewable gas production technology, has gained significant attention for its potential in enhancing soil fertility, nutrient retention, and its gradual release. Further, biochar also serves as a potential mean for carbon sequestration and storage, reducing greenhouse gas emissions in the atmosphere.

However, it has not been fully demonstrated how biochar should be applied to soil. Issues such as the application technique, interaction with other components, impact on soil microorganisms, long-term effects, etc. have not yet been assessed consistently. This evaluation is crucial to avoid issues that could worsen the soil quality in the long-term.

The aim of Project FENIX is to find the most effective types of biochar, combine them with digestates (another renewable gas production byproduct) and evaluate the best formulation targeted to different soils.

To prove its efficacy and mid-long-term benefits, tests will be conducted in five distinct areas to assess their effectiveness in enhancing soil fertility, water retention, but also mitigating the growing problem of land desertification due to climate change.

Digestate is a subproduct we obtain from anaerobic digestion, a renewable gas production technology to turn bio-waste into clean energy. Digestate is rich in minerals, nitrogen, and various elements essential for plant growth. So, instead of being waste, it becomes a valuable source of plant nutrients and proves to be an effective component for enhancing crop development.

Despite its potential benefits, digestates are often considered low-value by-products in many regions, generating disposal costs rather than revenues. In FENIX, to make digestates more valuable, we plan to mix them with biochar to formulate an amendment product. We plan to collect digestates from a biogas plant located in France, test different formulations and analyse their characteristics, including mineral composition and nutrient content to ensure a comprehensive understanding of the benefits they can offer. By doing so, digestates can provide more effectively essential nutrients (N,P,K) and organic matter to the soil.

Therefore, the FENIX project aims to improve soil quality through the adoption of sustainable farming practices, thereby increasing agricultural productivity.

In the last decades, overuse of agrochemicals together with unsustainable agricultural practices have pose a risk in the health of soils, resulting on serious ecological problems, decrease of the quality of soil and the consequently increase of production costs. This issue is also very interrelated to global warming, biodiversity loss, toxic contamination, and the phenomenon of erosion, which will increasingly lead to arable soil resources loss every year.

Being one the main challenges of modern agriculture, several research has been made looking for alternative practices and products to decrease the risk of land erosion. Known from centuries, natural soil amendments can be an effective solution.

Project FENIX will explore the synergies out of the combination of two types of organic matter obtained from renewable gas production (biochar and digestates) to obtain a regulated/labelled soil amendment product targeted to poor soils. The nutrient rich mixture is expected to improve soil fertility, water-holding capacity, nutrient uptake and stimulating microbial activity at the same time it provides economic returns to the agricultural sector.

Although many studies have been carried out to characterize and quantify the effects of the application of biochar or digestate alone on soil physical properties, relatively little is known about their effects in case of combined applications. For example, the effect of biochar depends on several factors including soil type, climatic conditions, additional fertilizer application, feedstock type and processing conditions. Furthermore, the method of mixing the biochar and the digestate should also be considered as it may significantly affect the release of nutrients and the gaseous losses after the application.

FENIX will propose a methodology to optimize this agricultural combination. This includes both the selection and the processing conditions, the formulation of the biochar-digestate mixture and the preparation method and application in the field. The agronomic and environmental performances of the formulated product will be tested from lab to pilot scale, and under contrasting pedoclimatic conditions. Numerical models will be adapted to simulate the long-term agronomic and environmental effects of different scenarios of use of the product.

The soils in the southern Spain are frequently basic, nutrient-poor, and in some cases, have suffered from severe erosion processes. The Mediterranean climate and certain crops have degraded some soils to the point where they have had to be abandoned. In FENIX project we have selected three soils with different properties and uses. Two of them are cultivated soils (one with olive trees and the other with avocados). The olive soil is the most balanced of the three, although its organic carbon and nutrient content, such as phosphorus, could be increased. The avocado soil has a sandy loam texture. Its cation-exchange capacity is low, as is its ability to retain available water. Both properties could be significantly improved. The third soil selected is an old cereal crop that was abandoned about 40 years ago. It is now a wasteland with low water retention capacity and low nutrient content, especially phosphorus and potassium.

The soils selected in Greece for the FENIX project, used for cereal cultivation, have a balanced texture. It has a low content of calcium carbonate; however, despite this, its pH is alkaline. The cation exchange capacity in soils depends on the clay and organic matter contents. Although this Greek soil has the highest cation exchange capacity among the selected soils, this is primarily due to its clay content, as it has a very low organic carbon content. The available phosphorus content is also very low, as is the enzymatic activity of phosphoric monoester hydrolases which play an important role in the phosphorus cycle.

Increasing the organic carbon content could significantly improve the properties of this soil. First, it would improve the cation exchange capacity, thus enhancing the soil’s ability to retain nutrients in exchangeable positions, making them easily accessible to crops but protected from loss through leaching. Second, it would improve other properties, such as water retention capacity.

The soil selected in France for being analysed in the FENIX project is used for cereal cultivation. The texture is dominated by fine fractions: coarse silt, fine silt, and clay, with sand being a very minor component. This texture favours the retention of available water, especially if the soil is located in a humid climate that allows for the replenishment of the water reserve. It is a soil very poor in organic carbon, which, along with the low clay content, results in a very low cation exchange capacity, the lowest of all the selected soils between France, Greece and Spain. Despite this low cation exchange capacity, the soil has a base saturation degree slightly above 50% (the threshold separating saturated soils from unsaturated ones), as it contains very low amounts of sodium, calcium, and magnesium in the exchange complex. As a result, its pH is acidic (pH = 6). Increasing the organic carbon content and pH of this soil could significantly improve its fertility.

In the framework of soil organic products from recycled bio-waste, in producing soil products from biogas, all input materials must comply with the EU Fertilising Products Regulation (FPR, EU Reg. 1009/2009) ensuring their safety and authorization. For example, biochar must be tested for moisture, ash content, volatile matter, aromatic compounds, dioxins, carbon, hydrogen, heavy metals and pathogens to ensure safety. To meet legal requirements, it is required REACH certification, which includes toxicity and eco-toxicity tests. However, joining the biochar consortium or obtaining a letter of access can simplify this process by leveraging existing its certification, avoiding redundant tests.

Biochar itself is highly insoluble in water and cannot enter living cells due to its large particle size, meaning it poses no risk of bioaccumulation. Potential risks are associated with contaminants such as heavy metals or PAHs. However, as long as contamination levels are kept low, biochar is considered safe for use and does not pose significant environmental or biological risks.

Traditional methods of managing biowaste and green waste, such as burning biomass in fields, are still widely used, particularly in conventional agriculture. This practice releases significant amounts of greenhouse gases (GHG) and harmful pollutants, contributing to air quality degradation and climate change. While innovative alternatives are available, they are not yet widely adopted due to economic, practical constraints, and limited public awareness.
The FENIX EU Project offers an innovative way to turn biowaste and green waste into biochar using a process called pyrolysis. This method heats the biomass at high temperatures without oxygen, preventing combustion and transforming it into biochar—a stable, carbon-rich material—and syngas.

Biochar provides two major benefits that are especially relevant for farmers. First, it offers a long-term solution for carbon storage, as it remains stable in soils for many years, capturing carbon and reducing GHG emissions. Second, it improves soil health by increasing water retention and capturing nutrients, making it an excellent tool for enhancing soil fertility and productivity.