UPMSP Soil Conservation (Vocational) flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Soil texture triangle

A USDA diagram that classifies soil into 12 textural classes from the percentages of sand, silt and clay. Boundaries are read by following the three axes to their intersection point.

Bulk density

The oven-dry mass of soil divided by its total volume, including pore space. Expressed in g/cm³, it rises with compaction and falls with organic matter; porosity is derived from it.

Jenny's soil formation equation

S = f(climate, organisms, relief, parent material, time). These five state factors control the direction and rate of soil development and explain differences between profiles on the same landscape.

Eluviation and illuviation

Eluviation is the removal of clay, iron or organic matter from an upper horizon, forming an E horizon. Illuviation is their deposition in a lower B horizon, producing clay-enriched Bt horizons.

Universal Soil Loss Equation

A = R × K × LS × C × P. It estimates long-term average annual soil loss from sheet and rill erosion on a slope, with rainfall, soil, topography, cover and support practice as factors.

Rill versus gully erosion

Rills are small concentrated-flow channels under about 30 cm deep that are smoothed by normal tillage. Gullies are deeper channels that tillage cannot obliterate and need structural treatment.

Saltation

The bouncing transport of sand-sized particles by wind, lifted briefly and dropped back to dislodge others. It accounts for most wind-eroded soil mass and drives surface creep and dust suspension.

Rainfall erosivity (R)

A USLE factor expressing the erosive power of rainfall, computed as storm kinetic energy multiplied by the maximum 30-minute intensity (EI30). It is highest in regions of intense convective storms.

Contour bund

An earth embankment built along a contour to intercept runoff and hold it on the slope. Suited to rainfall of about 500–800 mm and slopes up to 6–8 percent.

Vertical interval

The elevation difference between successive conservation structures such as bunds or terraces. It is estimated from slope and strip width and converted to horizontal spacing for field layout.

Strip cropping

An agronomic measure in which alternating strips of erosion-resistant cover and row crops are laid along the contour. Strips filter runoff and trap sediment before it concentrates.

Grassed waterway

A vegetated channel that carries concentrated runoff down a slope at a non-erosive velocity. It is the safe outlet for terraces, bunds and diversions and must be maintained free of bare patches.

Watershed divide

The ridge line separating two drainage basins, drawn perpendicular to contours through the highest ground. It defines the boundary used to compute watershed area and layout conservation works.

Rational method

Q = C·I·A/3.6, giving peak runoff in m³/s from runoff coefficient C, rainfall intensity I in mm/h and catchment area A in km². Used for small catchments and structure design.

First flush

The initial portion of roof runoff, carrying dust, bird droppings and debris. Discarding the first 1–2 mm of rainfall protects stored water quality and reduces tank sediment.

Farm pond capacity

The volume of a dugout or embankment pond, computed from base area, top area, depth and side slopes. The prismoidal formula gives the most accurate earthwork and storage estimate.

Cation exchange capacity

The total exchangeable cations a soil can hold, in cmol(+)/kg. It is high in smectite clays and humus, low in kaolinite and sands, and governs nutrient retention and lime requirement.

Law of the minimum

Yield is limited by the nutrient in shortest supply relative to crop need, not by total nutrient abundance. Correcting the most deficient nutrient gives the largest yield response.

Integrated nutrient management

The combined use of mineral fertilizers, organic manures, green manure and biofertilizers to meet crop nutrient needs while maintaining soil organic matter and reducing nutrient losses.

Soil health card

A report of soil test values including pH, electrical conductivity, organic carbon, available nitrogen, phosphorus, potassium, sulphur and micronutrients, with crop-wise fertilizer recommendations.

Field capacity

The water content remaining in soil after free drainage has ceased, held at about −33 kPa. It is the upper limit of plant-available water and the target after irrigation.

Available water capacity

The water held between field capacity and permanent wilting point, expressed in mm per metre of soil depth. It is larger in loams and clays than in sands and sets irrigation intervals.

Drip irrigation

A method delivering water slowly through emitters to the root zone. It saves 30–50 percent water over surface flooding, limits evaporation and allows fertigation with precise placement.

Mulching

Covering the soil surface with crop residue, straw or plastic film to reduce evaporation, moderate soil temperature, suppress weeds and protect the surface from raindrop impact.

Land equivalent ratio

LER = sum of (yield of each crop in intercrop / its sole-crop yield). A value above 1 means intercropping uses land more efficiently than separate sole crops.

Alley cropping

An agroforestry practice with hedgerows of fast-growing trees or shrubs between crop alleys. Prunings supply mulch and nitrogen while roots and stems reduce runoff and soil loss.

Land capability class

A classification from I to VIII reflecting increasing limitations for use. Classes I–IV are arable, V–VII suit pasture or forestry, and VIII is reserved for protection and recreation.

Conservation agriculture

A farming system based on minimum soil disturbance, permanent organic soil cover and crop species diversification. It reduces erosion, conserves moisture and improves soil structure over time.

Reduced level

The elevation of a survey point relative to a benchmark. It is computed as height of instrument minus staff reading, with the instrument height set from the benchmark backsight.

Contour interval

The vertical distance between adjacent contour lines on a map. It is chosen from map scale and terrain relief; closer intervals depict gentler slopes and finer landform detail.

Trapezoidal rule

An area formula for equally spaced offsets: A = d[(O1 + On)/2 + O2 + … + O(n−1)]. It approximates the boundary as straight segments between measured offsets.

Check dam

A small barrier built across a gully or stream to slow flow, reduce bed gradient and trap sediment. Materials include gabion, loose boulder, brushwood and masonry, each needing a safe spillway.