Soil and Water Conservation and Land Management
Core concepts
Understand soil erosion types-sheet, rill, gully, and wind erosion-and the factors in the Universal Soil Loss Equation (rainfall erosivity, soil erodibility, slope length and steepness, cover management, and support practice). Know conservation structures and practices: contour farming, terracing, strip cropping, grassed waterways, check dams, mulching, and conservation tillage. Grasp the hydrologic cycle components (infiltration, percolation, runoff, evapotranspiration) and how land use alters them. Understand soil moisture conservation, irrigation scheduling, drainage, and salinity/sodicity management (leaching requirement, gypsum for sodic soils).
Traps in questions
Distinguish rill erosion (small channels removable by tillage) from gully erosion (channels too deep to cross with ordinary tillage). Do not confuse soil erosion (detachment and transport) with soil loss tolerance. Remember that contour farming reduces slope-length effect, not slope steepness itself. Watch for questions confusing sodic soils (high exchangeable sodium, treated with gypsum) with saline soils (high soluble salts, treated by leaching).
Worked example
A field has a 6% slope and 120 m slope length. Converting slope percent to degrees: degrees ≈ arctan(0.06) ≈ 3.4°. Rule of thumb: slope percent = rise/run × 100; slope degrees = arctan(slope fraction). A 100% slope equals 45°, a common trap where examinees confuse percent with degrees.
Rule of thumb
Match the practice to the erosion process: vegetative cover for sheet and wind, structural measures (terraces, waterways) for concentrated flow.