Terracing is a method of reshaping sloped land into a series of flat, step-like platforms that run across a hillside. Each “step” creates a level surface for farming, slows the flow of rainwater, and prevents soil from washing downhill. It’s one of the oldest and most effective techniques for turning steep, erosion-prone terrain into productive farmland, and roughly 853,000 square kilometers of cropland worldwide (about 5.1% of all global cropland) is terraced today.
How Terracing Works
Picture a staircase carved into a hillside. Each step has a flat or gently sloped surface where crops grow, and a vertical or near-vertical wall (called a riser) that holds the soil in place below it. When rain falls on a smooth slope, water picks up speed as it flows downhill, carrying topsoil with it. Terraces interrupt that process by catching water on each flat step, giving it time to soak into the ground instead of rushing away.
The results are dramatic. Field studies in Rwanda found that terracing reduced water runoff by 70% to 85% depending on the site, and cut soil loss by as much as 93%. Even in steep mountainous areas, well-built terraces cut soil erosion roughly in half. That combination of holding water and holding soil is the fundamental reason terracing has been used for thousands of years across every inhabited continent.
Common Types of Terraces
Not all terraces look the same. The design depends on how steep the land is, what crops will grow there, and how much water needs to be managed.
- Bench terraces are the classic staircase design, with clearly defined flat platforms separated by steep risers. They’re typically built on slopes between 7 and 25 degrees. On gentler slopes (up to about 20 degrees), machines can build them; steeper terrain requires hand construction.
- Level bench terraces are a specialized version designed for crops like rice that need standing water. They include small raised edges (dykes) to hold water on each platform, with no slope at all across the surface.
- Contour terraces follow the natural curves of a hillside rather than cutting perfectly straight lines. They’re common on gentler slopes where full bench construction isn’t necessary, and they work well with standard farm equipment.
In the United States, the Natural Resources Conservation Service specifies that farmable terrace slopes should be no steeper than 5 to 1 (five feet horizontal for every one foot of vertical rise) so tractors and other equipment can operate safely. Non-farmable slopes, like the risers between platforms, can be as steep as 2 to 1.
What Terracing Does for Soil
Beyond simply preventing erosion, terracing changes the character of the soil itself over time. Terraced cropland holds onto finer particles like clay and silt that would otherwise wash away on an open slope. Those fine particles are important because they store nutrients and help soil retain moisture.
Terracing also increases the amount of organic carbon stored in soil. Research on China’s Loess Plateau found that terraced fields contained about 57% more organic carbon than comparable sloped fields (7.7 grams per kilogram versus 4.9). The effect is strongest in the top 30 centimeters of soil, where roots and decomposing plant material accumulate. Older terraces perform even better, because organic matter builds up gradually year after year. A terrace that has been in place for decades stores significantly more carbon than one built recently.
There’s a trade-off during construction, though. Building new terraces strips away existing topsoil, and it takes years for organic matter to rebuild. Freshly constructed terraces often have lower fertility than the original slope until the soil ecosystem reestablishes itself. Over the long term, the improved water retention and reduced erosion create conditions that favor steady carbon accumulation and healthier soil biology.
Ancient Engineering Still in Use
Terracing isn’t a modern invention. The Inca civilization built terraces across the Andes that are still studied by engineers today. At Machu Picchu, researchers from the University of Wisconsin found that the subsurface of the terraces follows a precise layering system: large stones at the bottom, then gravel, then sandy material, and finally topsoil on the surface. This layering provides structural strength while ensuring water drains at a controlled rate rather than pooling and destabilizing the walls. The terraces were also built with a slight outward slope to direct excess runoff into drainage channels that carried water safely away from the city.
Similar ancient terrace systems exist across Southeast Asia, the Mediterranean, and East Africa. Many are still actively farmed, which speaks to how durable the technique can be when properly maintained.
Maintenance That Keeps Terraces Working
Terraces are not a build-it-and-forget-it solution. Without regular upkeep, they can fail, sometimes catastrophically. The most common failure mode is overtopping, where water rises above the terrace ridge during a heavy storm and pours over the edge, eroding the structure from the top down. Standard engineering practice calls for terraces to handle at least a 10-year storm event (the kind of heavy rainfall you’d expect once a decade) without overtopping.
Routine maintenance includes inspecting the terraces after major rainstorms, repairing any damage to the ridges or risers, and removing sediment that accumulates in the drainage channels. Over time, sediment buildup reduces a terrace’s capacity to hold water, which increases the risk of overtopping. Burrowing animals can also compromise structural integrity by creating tunnels through the earthen walls. If the terrace includes underground drainage outlets, the inlets need regular cleaning and should be checked for damage from farm equipment. For terraces with vegetated slopes, seasonal mowing and control of trees and brush keeps roots from destabilizing the structure.
Costs and Practical Considerations
Building terraces is a significant investment. Construction costs vary widely depending on location, slope, soil type, and whether the work is done by hand or machine. As a reference point, one study estimated construction costs for a specific terrace design at roughly $6,300 per hectare (about $2,550 per acre), though real-world costs can range well above or below that figure depending on conditions.
The payoff comes gradually. Reduced erosion means less fertilizer washed away each season. Better water retention means crops survive dry spells that would stress plants on untreated slopes. Over years and decades, the improved soil quality compounds those benefits. For smallholder farmers on steep land in tropical regions, terracing can mean the difference between productive fields and land that degrades to the point of being unusable. For large-scale operations on moderate slopes, contour terraces that work with existing equipment offer erosion control without dramatically changing farming practices.