Soil quality is essential for agriculture and food production. However, there are several factors that can degrade and destroy soil quality over time. In this article, we will examine the main causes of poor soil quality and how they negatively impact the land.
Erosion is one of the biggest threats to soil quality worldwide. It removes the topsoil, which contains most of the organic matter and nutrients needed for plant growth. There are several types of erosion:
- Wind erosion: Strong winds can blow away topsoil, especially in flat, dry areas. This is a common problem in arid and semi-arid regions.
- Water erosion: Water from rainfall, flooding, or excessive irrigation can wash away topsoil. Sloped areas are particularly susceptible.
- Tillage erosion: Traditional plowing and tilling methods disturb the soil and make it prone to erosion.
As erosion strips away the topsoil, the underlying subsoil is exposed. Subsoil tends to have less organic matter, fertility, and capacity to store water. This makes it much harder for farmers to grow crops there.
Loss of organic matter
Soil organic matter consists of decayed plant and animal residues. It is incredibly important for soil health because it:
- Stores nutrients and makes them available to plants gradually
- Helps bind soil particles into stable aggregates
- Increases the water holding capacity of soil
- Provides food for soil microbes
Regular tillage, erosion, lack of cover crops, overgrazing, and monocropping can all decrease soil organic matter over time. This deterioration leads to poorer soil structure, fewer nutrients, and increased compaction.
Growing crops remove substantial nutrients from the soil, especially nitrogen, phosphorus, and potassium. Without replenishment, soils can become depleted of nutrients. Signs of depletion include:
- Lower yields and poorer crop quality
- Stunted, yellowish plants
- Increased pest and disease damage
Nutrient depletion can be avoided by using fertilizer, compost, manure, and cover crops. Rotating different types of crops can also help by varying nutrient uptake.
Salinization is the buildup of soluble salts in soil. It most often occurs in arid regions where irrigation water evaporates and leaves salts behind. Salts can also rise up naturally from groundwater. Salinization makes it very difficult for plants to absorb water and nutrients. Even salt-tolerant crops suffer reduced yields at higher salt levels.
Soil acidity refers to the concentration of hydrogen ions. A pH below 7 is acidic. Acidic conditions have several detrimental effects:
- Reduces availability of essential nutrients like phosphorus, calcium and magnesium
- Promotes aluminum, iron, and manganese toxicity
- Impairs root growth and function
Common causes of soil acidification include use of acid-forming fertilizers, heavy cropping without liming, and nitrogen fixation by legumes. Liming is commonly used to counteract acidification.
Compacted soil has been compressed, reducing pore space. This creates a dense, hard layer that restricts root growth and water infiltration. Machinery and livestock trafficking are major causes of compaction. It can be alleviated by subsoiling, avoiding traffic on wet soils, and using cover crops with deep root systems.
Chemical contamination of soils has occurred due to industrial activity, waste disposal, mining, agriculture, and more. Petroleum, metals, and solvents are common soil contaminants. Even at relatively low concentrations, most contaminants degrade soil quality and pose health risks. Remediation can be challenging and expensive.
Loss of biodiversity
Healthy soils have an immense diversity of microorganisms like bacteria, fungi, protozoa, and nematodes. These organisms are vital for:
- Decomposing organic matter and releasing nutrients
- Building soil structure and stabilizing aggregates
- Supporting plant health and nutrient uptake
- Detoxifying pollutants
Loss of soil biodiversity has been linked to practices like monocropping, tillage, pesticides, and excessive inputs. It can degrade key soil functions and health.
Desertification is the degradation of drylands into desert-like conditions. It involves extreme soil erosion and loss of organic matter, nutrients, and vegetation. Desertification can occur due to drought, climate change, overgrazing, and unsustainable farming. Vast regions including the Mediterranean, Central Asia, and Sub-Saharan Africa are threatened by desertification.
Soil quality declines over time when managed poorly. Practices like monocropping, over-tilling, excessive inputs, and failing to control erosion take a toll. Loss of organic matter, biodiversity, and nutrients makes soils unproductive. Conservation farming techniques such as no-till, cover crops, crop rotation, and wise inputs can protect and enhance soils.