Several common practices damage the land, but the most widespread are monoculture farming, overgrazing, deforestation, improper irrigation, mining, and urban development. Between 2015 and 2019 alone, the global proportion of degraded land rose from 11.3 to 15.5 percent, affecting the well-being of an estimated 3.2 billion people. Understanding how each practice harms the soil helps explain why land degradation is accelerating and why recovery is so slow: it takes 500 to 1,000 years for just one inch of topsoil to form naturally.
Monoculture Farming
Growing the same crop on the same land year after year, known as monoculture, is one of the most common practices that degrades soil. A 50-year study comparing monoculture rye fields to rotated cropland confirmed what scientists have long recognized: monocultures cause measurable soil degradation over time. Crop yields decline even with optimal fertilization, and the soil’s biological health suffers.
One telling indicator is earthworm populations. In that same long-term study, fields using crop rotation with row crops had 2.2 to 11.1 times more earthworms than monoculture plots. Earthworms are essential for soil health because they break down organic matter, create channels for water and air, and help maintain soil structure. When their populations collapse, the soil becomes more compacted and less fertile. Rotation with perennial grasses and periods of uncultivated soil substantially boosted earthworm numbers, while monoculture and intensive tillage suppressed them.
Pesticide and Chemical Use
Synthetic pesticides don’t just kill target pests. They also reduce populations of beneficial soil organisms that plants depend on. A large meta-analysis of pesticide impacts found that across studies, pesticide-treated soils showed significant declines in multiple categories of microbial life, including fungi that form symbiotic relationships with plant roots (called arbuscular mycorrhizal fungi). These fungi help plants absorb water and nutrients, so losing them weakens the entire growing system.
Pesticides also reduced the activity of key soil enzymes responsible for breaking down organic matter and cycling nutrients like nitrogen and phosphorus. Fungicides were particularly damaging because fungi share biochemical pathways with the organisms these chemicals are designed to kill. Over time, repeated chemical application creates soil that looks normal on the surface but has lost much of its living infrastructure.
Deforestation and Soil Erosion
Removing trees strips the land of its most effective erosion defense. A study in western Iran measured this directly: forested hillslopes lost about 5 to 6 metric tons of soil per hectare each year, while nearby land cleared for vineyards lost 26 to 33 metric tons per hectare annually. That’s roughly five times the erosion rate. Tree roots hold soil in place, and the canopy breaks the force of rainfall before it hits the ground. Without them, rain washes topsoil downhill, carrying nutrients and organic matter with it.
Because topsoil forms at roughly one inch per millennium, the math is sobering. A single generation of deforestation can strip away soil that took thousands of years to develop, and replanting trees doesn’t reverse the damage on any human timescale.
Overgrazing by Livestock
Overgrazing isn’t simply about too many animals on too little land. It’s defined by timing. If livestock graze a pasture, the plants begin to regrow, and then the animals graze those same plants again before they’ve recovered, that’s overgrazing. The critical factor is continuous grazing pressure without adequate rest periods.
The damage follows a chain reaction. Repeated hoof traffic compacts the soil, reducing the pore space that normally holds air and water. Compacted soil absorbs less rainfall, which increases runoff and erosion. Meanwhile, plants that are constantly regrazed can’t rebuild their root systems or produce enough leaf area to photosynthesize effectively. Eventually, vegetation thins out entirely, leaving bare soil exposed to wind and water. In severe cases, this process leads to desertification, where formerly productive rangeland becomes barren.
Improper Irrigation and Salt Buildup
Irrigation keeps much of the world’s farmland productive, but done poorly, it poisons the very soil it’s meant to nourish. The problem is salt. All irrigation water contains dissolved minerals, and when water evaporates or is absorbed by plant roots, those salts stay behind in the soil. Healthy irrigation systems flush salts below the root zone periodically, but inefficient systems let them accumulate.
Over-irrigation raises the water table, which brings deeper salts up into the root zone. Under-irrigation fails to leach salts that build up from the water itself. Both extremes cause damage. Once soil salinity passes a certain threshold, most food crops simply can’t extract enough water from the soil to survive. At advanced stages, salt crystals become visible on the soil surface, groundcover disappears entirely, and the exposed soil erodes rapidly. Mismatching the crop type, soil type, and irrigation method accelerates the problem.
Mining and Heavy Metal Contamination
Strip mining and other extractive operations remove topsoil entirely, but the contamination they leave behind is often worse than the physical destruction. A comprehensive assessment of non-ferrous metal mining sites worldwide found that mercury and cadmium are the two metals posing the greatest soil pollution risk across all mining types. Arsenic and copper ranked close behind.
The severity varies by mine type. Copper mines in China, Russia, and Portugal showed the most extreme arsenic contamination. Lead-zinc mines across Tunisia, China, Ireland, Spain, and several other countries had the worst cadmium levels. Gold mines in Iran, China, Myanmar, Brazil, and Nigeria produced the highest mercury contamination. These metals don’t break down. They persist in the soil indefinitely, entering the food chain through plants that absorb them and the animals that eat those plants.
Landfills and Waste Disposal
Landfills concentrate a cocktail of toxic substances in one location, and those substances don’t stay put. As rainwater filters through waste, it picks up heavy metals like lead, cadmium, chromium, copper, and nickel, along with aromatic hydrocarbons, pesticide residues, phenols, and plasticizers. This toxic liquid, called leachate, seeps into surrounding soil and water.
Studies around unlined landfill sites have found contamination in surface water and groundwater within a 1-kilometer radius. Vegetables and rice grown near these sites absorbed enough lead and nickel to pose carcinogenic risk to people eating them. The health risk index for toxic heavy metals in crops near landfills was classified as high, meaning the contamination wasn’t just detectable but genuinely dangerous.
Urban Sprawl and Soil Sealing
When cities expand, they cover soil with concrete, asphalt, and buildings. This process, called soil sealing, is essentially permanent. Paving over soil blocks the exchange of gases, water, and energy between the ground and the atmosphere. The soil beneath can no longer filter rainwater, store carbon, support plant life, or host the microbial ecosystems that make land fertile.
A 15-year study of urban expansion in China documented how converting natural and agricultural land to impermeable surfaces was the leading cause of soil function loss in the region. Unlike other forms of land degradation, soil sealing is nearly impossible to reverse without enormous cost. Even if pavement is removed, the soil underneath has often been so compacted and depleted that it can take decades to regain basic function. Every new parking lot or subdivision represents a permanent withdrawal from a resource that took centuries to form.