Soil is a vital living system with the capacity to sustain plant and animal productivity, regulate water and air quality, and support ecological balance. Agricultural practices have a direct and long-lasting impact on soil health. This article examines the effects of fertilizer application, tillage practices, organic amendments, and biochar on soil physical, chemical, and biological properties.
1. Impact of Fertilizer Application on Soil Health
1.1 Effects on Soil Physical and Chemical Properties
Chemical fertilizers, especially nitrogen (N), phosphorus (P), and potassium (K), can enhance soil fertility in the short term. However, long-term excessive nitrogen input disrupts soil carbon-nitrogen (C:N) balance and leads to the decline of soil organic matter. This results in the breakdown of large soil aggregates into smaller ones, causing soil compaction and reduced nutrient-holding capacity.
Excessive nitrogen use also promotes soil acidification through nitrification and leaching of base cations. Acidified soils increase the availability of trace metals like Zn, Fe, Mn, and Cu, but also elevate harmful elements such as cadmium (Cd) and aluminum (Al), posing food safety risks. Additionally, high nitrogen input raises greenhouse gas emissions, especially nitrous oxide (N₂O), while reducing methane (CH₄) absorption due to inhibited methanotroph activity.
1.2 Effects on Soil Microbial Communities
Excess nitrogen reduces microbial diversity and weakens the stability of nitrogen-cycling microbial groups. Long-term application alters microbial structure due to changes in soil pH, C:N:P ratio, and osmotic pressure. Fungal-to-bacterial and Gram-negative-to-Gram-positive ratios decline, while lower pH and nutrient imbalance further suppress sensitive microbial groups. Microbial responses vary by soil type, with fungi generally more sensitive to nitrogen than bacteria.
2. Impact of Tillage Practices on Soil Health
2.1 Effects on Soil Physical and Chemical Properties
Conservation tillage practices, such as no-till, reduced tillage, and crop residue mulching, improve soil structure and reduce erosion. These methods increase water infiltration, storage, and aggregate stability. Crop residues supply carbon for aggregate formation, enhancing water retention and reducing greenhouse gas emissions.
However, long-term conservation tillage may lead to shallower root zones and reduced nutrient availability due to higher soil bulk density. In contrast, conventional plowing can break down soil structure, accelerate organic carbon loss, and increase N₂O emissions through intensified nitrification and denitrification.
2.2 Effects on Soil Microbial Communities
Conservation tillage increases microbial biomass, especially in the topsoil, by minimizing physical disturbance. Residue cover improves water and temperature regulation, stimulating microbial activity. Higher organic matter input promotes microbial diversity and nutrient cycling. Residue decomposition encourages the growth of copiotrophic fungi while reducing oligotrophic bacterial groups.
3. Impact of Organic Fertilization on Soil Health
3.1 Effects on Soil Physical and Chemical Properties
Organic fertilizers offer balanced nutrition and long-lasting effects. They improve soil porosity, water-holding capacity, and nutrient availability. During decomposition, organic matter produces humus, fungal hyphae, and polysaccharides that bind soil particles into stable aggregates. Organic acids released in the process enhance mineral weathering and nutrient release, while trace elements like S, Mg, Fe, Mn, Cu, Zn, and B help alleviate micronutrient deficiencies.
3.2 Effects on Soil Microbial Communities
Organic fertilization boosts microbial activity by supplying nutrients and substrates. It increases microbial biomass carbon and nitrogen and introduces beneficial microbes and enzymes. However, excessive use may disturb the soil C:N balance, lowering enzyme efficiency. Combining organic and chemical fertilizers can complement each other and support long-term ecosystem functioning.
4. Impact of Biochar Application on Soil Health
4.1 Effects on Soil Physical and Chemical Properties
Biochar improves soil structure by increasing porosity, reducing bulk density, and enhancing aeration and water retention. It promotes aggregate formation through interaction with native organic matter and cations like Ca²⁺ and Mg²⁺. Its alkaline nature neutralizes soil acidity and improves nutrient retention by reducing leaching.
4.2 Effects on Soil Microbial Communities
Biochar’s porous structure offers favorable microhabitats for microbial colonization. It promotes the growth of beneficial organisms such as arbuscular mycorrhizal fungi and actinomycetes. Biochar also increases the stability of microbial habitats, supports nutrient cycling, and alters microbial community composition by raising soil pH. It enriches nitrifiers, nitrogen fixers, and cellulose degraders, enhancing overall soil microbial function.
Soil health is shaped by the interactions between agricultural inputs and biological processes. While chemical fertilizers and traditional tillage can degrade soil quality over time, conservation practices like organic amendments and biochar application offer sustainable solutions. A balanced approach that combines these strategies is essential to maintain productive, resilient, and environmentally sound agricultural systems.
