The application of biochar and sewage sludge (biosolids) as soil amendments can significantly influence soil physical, chemical, and biological properties, leading to enhanced soil fertility and crop productivity. These amendments interact with soil systems through distinct yet complementary mechanisms, which vary depending on soil type and cropping systems.

Physical Properties: Biochar improves soil structure by increasing porosity, water retention, and aggregation, particularly in sandy or degraded soils. Its porous nature enhances aeration and reduces soil compaction, facilitating root penetration and water infiltration. Sewage sludge, rich in organic matter, also improves soil structure by increasing aggregation and water-holding capacity, especially in clayey soils. However, excessive application of sludge can lead to soil compaction over time, highlighting the need for balanced use.

Chemical Properties: Biochar enhances soil chemical properties by increasing cation exchange capacity (CEC), which improves nutrient retention and reduces leaching of essential nutrients like potassium, calcium, and magnesium. It also stabilizes soil pH, making it particularly beneficial in acidic soils. Sewage sludge provides a direct source of macronutrients (nitrogen, phosphorus, and potassium) and micronutrients, which are readily available for plant uptake. However, its application must be monitored to avoid heavy metal accumulation and nutrient imbalances, especially in sensitive soils.

Biological Properties: Both amendments stimulate microbial activity, but through different mechanisms. Biochar provides a stable habitat for beneficial microbes due to its porous structure, promoting the growth of microorganisms involved in nutrient cycling, such as Rhizobium and Bacillus. These microbes enhance nitrogen fixation, phosphorus solubilization, and hormone production, directly benefiting plant growth. Sewage sludge, being rich in organic matter, serves as an immediate energy source for soil microbes, leading to a temporary surge in microbial biomass and activity. Over time, however, the effects of sludge may diminish unless supplemented with additional organic inputs.

Mechanisms for Enhancing Soil Fertility and Crop Productivity:

In my research, I observed that the integration of biochar with beneficial microbes like Rhizobium and Bacillus significantly improved the growth and yield of Capsicum. The porous structure of biochar provided a habitat for these microbes, enhancing their survival and activity. Rhizobium increased nitrogen availability, while Bacillus solubilized phosphorus and produced growth hormones, leading to healthier plants and higher yields. Sewage sludge, while beneficial in the short term, required careful management to avoid nutrient imbalances. Overall, the synergistic effects of biochar and microbial inoculants proved more sustainable for long-term soil health and crop productivity across different soil types

The application of biochar and sewage sludge can significantly influence soil physical, chemical, and biological properties in both beneficial and potentially adverse ways. Here’s a breakdown:

1. Physical Properties

• Soil Structure & Aggregation: :Biochar enhances soil aggregation by improving soil porosity and reducing bulk density. Sewage sludge contributes organic matter, improving soil structure and aeration.
• Water Retention & Infiltration: Biochar increases water-holding capacity, particularly in sandy soils. Sewage sludge enhances moisture retention due to its high organic matter and humic substances.
• Bulk Density & Compaction: Biochar reduces bulk density, making the soil lighter and more aerated. Sewage sludge can sometimes increase bulk density in heavy applications but generally helps loosen compacted soils.

2. Chemical Properties

• Soil pH: Biochar, especially from alkaline feedstocks, increases soil pH, benefiting acidic soils. Sewage sludge may either increase or decrease pH depending on its composition.
• Nutrient Availability: Biochar improves cation exchange capacity (CEC), helping retain nutrients like potassium (K), calcium (Ca), and magnesium (Mg). Sewage sludge provides essential nutrients such as nitrogen (N), phosphorus (P), and micronutrients.
• Soil Organic Carbon (SOC):Biochar is highly recalcitrant and contributes long-term carbon sequestration. Sewage sludge adds labile organic matter, enhancing microbial activity and short-term carbon dynamics.
• Heavy Metals & Contaminants: Sewage sludge may introduce heavy metals (Cd, Pb, Zn, etc.), requiring careful management. Biochar can adsorb heavy metals and reduce their bioavailability, mitigating potential risks.

3. Biological Properties

• Enzyme Activities y & Diversity: Biochar creates microhabitats that can promote microbial diversity and activity. Sewage sludge provides organic substrates that stimulate microbial growth and enzyme activities.
• Enzyme Activities: Both amendments enhance enzymatic activities related to nutrient cycling (e.g., phosphatase, urease, dehydrogenase).
• Soil Respiration & Carbon Cycling: Biochar stabilizes organic matter, reducing microbial respiration rates. Sewage sludge increases microbial respiration due to its readily decomposable organic fractions.
• Pathogen Risks: Sewage sludge may contain pathogens, but proper treatment (e.g., composting) can mitigate risks. Biochar can help suppress certain soil-borne pathogens by modifying the soil microbiome.

Overall Impacts

• Synergistic Benefits: Combining biochar with sewage sludge can enhance nutrient retention, improve soil structure, and promote microbial activity while reducing heavy metal bioavailability.
• Potential Risks: Over-application of sewage sludge may lead to heavy metal accumulation and organic pollutant concerns. Biochar can counteract some of these risks, but its effects depend on feedstock and pyrolysis conditions.

Taking in to account the above mentioned synergistic functions of biochar and sewage sludge, studying their effect on the volatilization of Nutrient Nitrogen (the most dynamic and deficient nutrient) is also crucial.

Bonsoir!

• La fertilisation chimique ou biochimique ne semble pas tout à fait faire l'unanimité. Il est connu que la fertilisation (N,P,K) est incontournable,
• Elle contribue à augmenter la production agricole, toutefois il faut être attentif concernant leur usage (choix de leur composition, leur provenance, etc.....).
• D'autre part les scories (éléments métalliques fournissant des éléments comme le Na+, le Mg++, le Ca++),
• Certaines d'entre elles peuvent comporter d'autres substances toxiques qui nuisent aux cultures on peut dire!
• On ne pourra jamais le répéter assez donc attention à ces usages utiles non réglementés qui porteront malheureusement préjudice aux sols et à l'agriculture en général.