Soil gets fertilized primarily through the addition of nutrients, both naturally and artificially, that are essential for plant growth. This occurs through the decomposition of organic matter and/or the application of inorganic fertilizers.
Natural Fertilization Processes
The primary method of natural soil fertilization involves the decomposition of organic materials:
- Decomposition of Organic Matter: Plant debris (leaves, stems, roots) and animal waste are broken down by microorganisms (bacteria, fungi) in the soil. This process, known as mineralization, releases inorganic nutrients into the soil.
- Nitrogen Fixation: Certain bacteria, such as Rhizobium in legume root nodules, convert atmospheric nitrogen into ammonia, a form plants can use.
- Animal Activity: Earthworms, insects, and other soil organisms improve soil structure, aeration, and nutrient cycling through their burrowing and feeding activities. Animal waste also contribute to fertilization.
- Weathering of Rocks: Over long periods, the weathering of rocks releases minerals into the soil, enriching it with nutrients. However, this is a very slow process.
Artificial Fertilization Processes
Artificial fertilization involves the application of commercially produced fertilizers:
- Inorganic (Chemical) Fertilizers: These fertilizers contain concentrated nutrients (nitrogen, phosphorus, potassium, and micronutrients) in readily available forms. They provide a quick boost to plant growth.
- Organic Fertilizers: These fertilizers are derived from natural sources such as manure, compost, bone meal, and blood meal. They release nutrients slowly and improve soil structure, water retention, and microbial activity.
- Green Manure: Planting cover crops (e.g., legumes) and plowing them back into the soil adds organic matter and nutrients.
- Lime Application: While not a fertilizer in the traditional sense, lime (calcium carbonate) is often added to acidic soils to raise the pH, making nutrients more available to plants.
Nutrient Cycling
Fertilization is fundamentally about enhancing the natural nutrient cycle within the soil. The process follows this cycle:
- Nutrient Input: Nutrients are introduced through natural or artificial processes.
- Plant Uptake: Plants absorb nutrients from the soil solution through their roots.
- Biomass Production: Nutrients are incorporated into plant tissues.
- Decomposition: When plants die or shed parts, the organic matter decomposes, returning nutrients to the soil.
- Nutrient Loss: Some nutrients can be lost through leaching, erosion, or volatilization. Effective fertilization strategies aim to minimize these losses.
The goal of fertilization is to provide plants with the nutrients they need in the right amounts and at the right time to optimize growth and yield, while maintaining soil health and minimizing environmental impacts.
