Contour planting is a foundational agricultural method designed to protect soil on sloping land. The practice involves performing all farming operations, including plowing, seeding, and cultivating, along the natural curves of the land’s elevation. This technique is an effective, low-cost strategy for soil conservation, mitigating water erosion on hillsides.
Defining Contour Planting
Contour planting involves aligning crop rows and tillage furrows perpendicular to the direction of the steepest slope. The rows follow the land’s contour lines, which are imaginary lines connecting points of equal elevation across the field. This creates a pattern of curving rows that wrap around the hillside, contrasting with straight-line planting common on flat fields.
The fundamental concept is that every plowed furrow and planted row is level, or very nearly level, running horizontally across the slope. Following these precise elevation lines ensures water is managed across the field’s surface. This precise layout is typically achieved through a topographic survey to establish a baseline contour line that all subsequent rows parallel.
The Mechanics of Erosion Control
The primary function of contour planting is to intercept and slow down the flow of water runoff from rainfall. When rows are planted up and down a slope, they create natural channels that allow water to rapidly gain speed and volume, leading to severe erosion. Contour rows, conversely, act as hundreds of miniature dams or reservoirs that break the water’s path.
The furrows and ridges created by tillage and planting operations hold rainfall in place, preventing it from rushing downhill. This reduction in water velocity prevents soil particles from being detached and carried away in the runoff, significantly decreasing sheet and rill erosion. Studies show that implementing contour farming alone can reduce soil loss by as much as 50 percent compared to traditional methods.
Slowing the water also provides a secondary benefit by greatly increasing the time available for infiltration. The water is held in the furrows, allowing more moisture to soak into the soil profile. This enhanced water retention conserves the topsoil and improves the overall soil moisture available for crop growth.
Ideal Implementation Conditions
Contour planting is most effective and appropriate on moderately sloping land where water erosion is a concern. The technique is typically recommended for slopes that range between 2 and 10 percent gradient. On land with a slope less than 2 percent, the risk of erosion is low, and the practice offers minimal benefit.
The effectiveness of the contour rows decreases significantly on steeper slopes, generally those exceeding 10 percent, because the volume and velocity of runoff can overwhelm the capacity of the small contour ridges. Furthermore, the practice works best on uniform slopes; fields with highly irregular or complex topography are poorly suited because it is difficult to maintain a consistent contour line.
Soil permeability is also a factor. Soils with slow infiltration rates may require a slight grade in the rows to ensure positive drainage and prevent excessive ponding that could damage crops.
Contextualizing Related Conservation Methods
Contour planting is one tool within a broader system of soil conservation practices, often used in conjunction with other methods. It is frequently compared to contour strip cropping, which is a more intensive practice.
Contour strip cropping alternates strips of cultivated crops with strips of dense, close-growing vegetation, such as hay or forage grasses, all planted along the contour. The sod strips in this method provide additional barriers and trap sediment, making it more effective than simple contour planting, especially on longer slopes.
Another related method is terracing, reserved for much steeper slopes that exceed the effective range of contour farming. Terracing involves the physical construction of level or nearly level benches across the slope, dramatically altering the land’s shape to create flat areas for cultivation. Unlike contour planting, terracing requires significant earth-moving but reduces soil loss by a greater margin on highly erodible land.