Ploughing across a slope, along lines joining points of equal height, to check soil erosion is called:

Contour ploughing (or contour farming) is the practice of ploughing and planting across a slope, following the contour lines (imaginary lines joining points of equal height), instead of ploughing up and down the slope.

How contour ploughing reduces erosion:

• The furrows and ridges created by ploughing along the contours act as small barriers that slow down the flow of rainwater down the slope.
• This reduces the speed of runoff, so less soil is washed away.
• More water soaks into the soil, improving soil moisture and groundwater recharge.

Where it is used:

• On gently sloping land in hilly and undulating regions, where water erosion is a problem.
• In India, it is used in parts of the Western Ghats, the Shivaliks, the Chota Nagpur plateau, and the ravine-affected areas of central India.

Other soil conservation methods:

Strip cropping: growing strips of crops (such as grains) alternately with strips of close-growing grasses or legumes across the slope. The grass strips trap soil and slow down wind and water.

Terrace farming: cutting broad, flat steps (terraces) into steep hill slopes to create level fields. Common in the Himalayas and north-eastern India.

Contour bunding: building small earthen embankments (bunds) along the contours to hold water and soil.

Gully plugging and check dams: blocking gullies to stop them from growing.

Afforestation: planting trees to bind the soil with their roots.

Zero tillage (no-till farming): sowing seeds directly without ploughing, which reduces erosion and fuel use.

Types of erosion:

• Sheet erosion: removal of a thin, uniform layer of topsoil.
• Rill erosion: small channels formed by running water.
• Gully erosion: deep channels; extensive gullying creates badlands, such as the Chambal ravines.
• Wind erosion: common in arid areas like the Thar Desert.

Why not the other options?

• ✗Strip cropping alternates strips of different crops across a slope.
• ✗Terrace farming creates step-like fields on steep slopes.
• ✗Zero tillage means sowing without ploughing.