UPMSP Soil Conservation (Vocational) cheat sheet

Soil is a three-phase system: mineral and organic solids (about 50% of volume), pore space split between water and air; a mineral soil at field capacity is roughly 25% water and 25% air by volume.

Texture classes follow the USDA triangle by sand (2.0–0.05 mm), silt (0.05–0.002 mm) and clay (<0.002 mm) percentages; the 12 textural classes are read from the triangle's band boundaries, not from a single dominant fraction.

Stokes' law governs sedimentation analysis (hydrometer method): settling velocity v = (2/9)·(ρs − ρw)·g·r²/μ, so a 0.002 mm particle settles about 100 times slower than a 0.02 mm particle.

Bulk density Db = oven-dry mass / total volume; particle density is taken as 2.65 g/cm³ for most mineral soils, so porosity (%) = (1 − Db/2.65) × 100.

Soil formation is described by the factorial model S = f(cl, o, r, p, t): climate, organisms, relief, parent material and time; Jenny's equation treats these as independent state factors.

Weathering sequence: physical (freeze–thaw, insolation, abrasion) produces fragments; chemical (hydrolysis, oxidation, carbonation, chelation) alters primary minerals; 2:1 clays form in moderate leaching, 1:1 kaolinite and oxides under strong leaching.

Soil profile horizons: O (litter), A (topsoil, maximum biological activity), E (eluvial loss), B (illuvial accumulation of clay, iron or carbonate), C (weathered parent material), R (hard bedrock).

Master horizons are subdivided (Ap, Bt, Bk, Bw) using subordinate symbols; a Bt horizon indicates clay illuviation, a Bk horizon indicates secondary carbonate accumulation in subhumid to arid climates.

Four soil-forming processes: additions (organic matter, dust, alluvium), losses (erosion, leaching, volatilization), translocation (eluviation/illuviation, bioturbation) and transformation (humification, mineral weathering).

Water erosion sequence by form: splash (raindrop impact detaches particles) → sheet (thin uniform removal) → rill (concentrated flow, <30 cm deep, obliterated by tillage) → gully (not obliterated by tillage) → stream-bank and mass movement.

The Universal Soil Loss Equation: A = R × K × LS × C × P, where A is soil loss (t/ha/yr), R rainfall erosivity, K soil erodibility, LS slope length–steepness, C cover-management and P support-practice factor; all factors are dimensionless except R and K.

Rainfall erosivity R = EI30, the product of storm kinetic energy and its 30-minute maximum intensity; K is measured on a standard 9% slope, 22.1 m long continuous-fallow plot.

Wind erosion requires three conditions together: an erodible dry surface, wind above the threshold velocity (about 5–6 m/s at 30 cm height for dry fine sand) and insufficient surface cover; transport modes are saltation (50–80% of mass), suspension and surface creep.

Slope steepness effect is non-linear: doubling slope steepness roughly doubles to triples soil loss, and LS rises with slope length to a power of about 0.4–0.5 (m = 0.5 for slopes above about 9%).

Erosion is accelerated when vegetative cover falls below about 30%; the C factor for continuous bare fallow is 1.0, for dense pasture about 0.01, so cover is the largest single lever in the USLE.

Gully classification by depth: shallow (<1 m), medium (1–3 m), deep (>3 m); by shape: V-shaped (young, active headcut), U-shaped (mature) and sapping gullies fed by subsurface seepage.

Mass wasting types on hill slopes: creep (slow, imperceptible), slump (rotational failure along a curved plane), debris flow and landslide; triggers are saturation, undercutting and loss of root reinforcement.

Erosion mapping indicators: exposed roots and pedestals, rills, sediment fans at slope bases, soil colour change, stone pavement lag and truncated horizon boundaries.

Contour bunds are recommended for rainfall of about 500–800 mm on slopes up to 6–8%; graded bunds are used where runoff must be safely diverted; bench terraces are used above about 15–16% slope or for irrigated horticulture.

Bund cross-section design: top width, side slopes (1:1 earth, 1.5:1 for unstable soils), depth and spacing from the vertical interval VI = (S × W)/(100 − S × W), with S slope % and W the horizontal width of the strip.

Vertical interval is also estimated with the formula VI (m) = 0.3 × slope % + 0.6 for bench terrace riser spacing; the horizontal interval HI = VI × 100 / slope %.

Terraces: bench (level, inward-sloping) for steep land and orchards; bench terraces are cut-and-fill with a riser protected by grass or stone pitching; outward-sloping bench terraces are not used on deep permeable soils.

Agronomic measures ranked by cost: contour ploughing and sowing, strip cropping (alternating strips of dense and row crops along the contour), mulching, cover cropping, crop rotation, vegetative barriers (vetiver, khus, napier) and minimum tillage.

Grassed waterways carry concentrated runoff at non-erosive velocity; permissible velocity depends on soil and cover (about 0.6 m/s for sandy soil, 1.2 m/s for clay, up to 1.8 m/s for grassed channels).

Check dams in gullies: brushwood, loose boulder, gabion and masonry; they reduce channel gradient and trap sediment; spacing is set by the height of the structure and the bed slope so that the upstream toe of one dam meets the crest of the next.

Contour trench and staggered trench are used on non-arable land above 15–20% slope for afforestation and pasture development, not for cropland.

Permanent structures must be combined with vegetation: a bund without a grassed back slope or a terrace without a riser cover fails by overtopping in a single high-intensity storm.

Watershed is the area draining to a common outlet; delineate on a topographic map by drawing ridge lines perpendicular to contours, starting at the outlet and closing on the highest ridge.

Morphometric parameters: area, perimeter, stream order (Strahler), bifurcation ratio, drainage density Dd = total stream length / area, and form factor = area / (basin length)²; a high drainage density indicates rapid runoff response.

Time of concentration Tc governs peak flow design; empirical Kirpich equation: Tc (min) = 0.0195 · L^0.77 · S^−0.385, with L channel length in metres and S channel slope.

Peak runoff by the rational method: Q = C·I·A/3.6 (Q in m³/s, I in mm/h, A in km²); C is about 0.1–0.2 for forest, 0.3–0.5 for cultivated land, 0.7–0.9 for paved surfaces.

Rainwater harvesting components: catchment (roof or treated ground), conveyance (gutters, channels), first-flush device, filter, storage tank or recharge pit; first flush discards the first 1–2 mm of rainfall.

Storage volume estimate: V = R × A × Cr, where R is annual or design rainfall, A catchment area and Cr runoff coefficient; a 100 m² roof with 800 mm rainfall and Cr 0.8 yields about 64 m³ per year.

Farm pond design: side slopes 1:1 to 2:1, depth 2–3 m, embankment freeboard 0.3–0.5 m, and a surplus weir for safe overflow; the pond capacity is computed by the prismoidal or trapezoidal formula.

Trapezoidal pond volume: V = (d/6)·[(A_base + A_top + 4·A_mid)] or equivalently V = d·(A_base + A_top)/2 when side slopes are uniform; use the prismoidal formula for accurate earthwork.

Recharge structures: percolation tank, check dam, recharge shaft, dug well recharge and contour trench; they are placed on permeable formations and avoid clay-rich strata that clog.

Essential nutrients: 17 elements; macro (N, P, K, Ca, Mg, S) plus C, H, O; micro (Fe, Mn, Zn, Cu, B, Mo, Cl, Ni); the law of the minimum states that yield is limited by the most deficient nutrient.

Soil pH controls availability: most nutrients are most available at pH 6.0–7.0; P is fixed by Al and Fe in acid soils and by Ca in alkaline soils; micronutrients (Fe, Mn, Zn) become deficient at high pH.

Cation exchange capacity (CEC) in cmol(+)/kg: kaolinite soils 3–15, illite 15–40, montmorillonite 80–150, humus 150–300; base saturation = (exchangeable bases / CEC) × 100.

Organic carbon and organic matter: soil organic matter ≈ soil organic carbon × 1.724 (Van Bemmelen factor); soil organic carbon above 0.75% in the plough layer is generally rated medium-to-high for Indian conditions.

Fertilizer grade expresses N–P2O5–K2O percentages; urea is 46-0-0, DAP 18-46-0, single superphosphate 0-16-0 plus 11% S and 19–21% Ca, muriate of potash 0-0-60.

Converting oxide to elemental: P = P2O5 × 0.436; K = K2O × 0.830; a 50 kg bag of urea supplies 23 kg N.

Soil test interpretation classes (low, medium, high) determine the fertilizer adjustment: high-testing soils receive a reduced dose, low-testing soils receive a built-up dose above the recommended dose.

Integrated nutrient management combines organic sources (FYM, compost, green manure, vermicompost, biofertilizers) with mineral fertilizers so that organic sources supply roughly 25–50% of the N requirement without yield loss.

Soil health card parameters: pH, electrical conductivity, organic carbon, available N, P, K, S and micronutrients (Zn, Fe, Cu, Mn, B); sampling depth 0–15 cm for cultivated land, 0–30 cm for plantation crops.

Soil moisture constants: field capacity is the water held at about −33 kPa, permanent wilting point at −1500 kPa; available water capacity = FC − PWP, expressed in mm per metre depth.

Available water depends on texture: sandy soil about 60–80 mm/m, loam 140–180 mm/m, clay 160–200 mm/m; irrigation scheduling uses the allowable depletion (commonly 50% of AWC for field crops).

Depth of irrigation water to apply: d = (FC − current moisture) × root-zone depth; gross depth = net depth / application efficiency (surface 60–70%, sprinkler 70–80%, drip 85–95%).

Drip irrigation design: emitter discharge 2–4 L/h, lateral spacing matched to crop rows, and irrigation interval set by crop evapotranspiration; drip saves 30–50% water versus surface flooding.

Sprinkler uniformity is measured by the Christiansen uniformity coefficient; a value above 85% is acceptable; operating pressure must match the nozzle rating or distribution degrades.

Surface methods: basin (orchard), border (close-growing crops), furrow (row crops, ridge-and-furrow); check basin is suited to permeable soils and small gradients.

Soil moisture conservation in situ: mulching (straw, plastic, crop residue), conservation tillage, contour furrows, deep ploughing once in 2–3 years to break the plough pan, and summer ploughing to store monsoon rainfall.

Evapotranspiration reference (ET0) via pan evaporation: ET0 ≈ Kp × Epan with pan coefficient Kp about 0.65–0.85; crop ET = Kc × ET0.

Antitranspirants and windbreaks reduce evaporative demand; a windbreak reduces wind speed for a distance of 10–20 times its height on the leeward side.

Cropping intensity (%) = (sum of cropped area in the year / net sown area) × 100; multiple cropping needs assured moisture, short-duration varieties and timely turnaround.

Cropping system types: sole cropping, multiple cropping (sequential and relay), intercropping (row, strip, mixed), and alley cropping; intercropping advantage is measured by the land equivalent ratio, LER = Σ(Yi mixed / Yi sole), with LER > 1 indicating advantage.

Crop rotation breaks pest and disease cycles and balances nutrient uptake; legumes fix 50–150 kg N/ha depending on species and conditions, contributing to the following cereal.

Agroforestry systems: agrisilviculture (crops + trees), silvopasture (trees + pasture/livestock), agrisilvopasture, homegarden, alley cropping, windbreak and shelterbelt, and riparian buffer.

Tree–crop interactions: competition for light, water and nutrients versus complementarity through hydraulic lift, nutrient pumping, shade and litter fall; root pruning and shoot pruning manage the competition.

Multipurpose tree selection criteria: deep root system, nitrogen fixation, fast growth, coppicing ability, low water demand and useful products; typical species include Leucaena, Gliricidia, Acacia, Dalbergia and subabul.

Sustainable land use capability classes I–VIII: I–IV are arable with increasing limitation, V–VII are suited to pasture, forestry or wildlife, VIII is for recreation and watershed protection; class and subclass (e.g. IIIe for erosion limitation) define the use.

Conservation agriculture has three principles: minimum mechanical soil disturbance, permanent organic soil cover, and species diversification through rotation; it reduces erosion and improves infiltration.

Shelterbelt design: rows perpendicular to the prevailing wind, height and porosity of about 40–50%, and spacing of 20–30 times tree height between belts.

Chain survey: measure the baseline and offsets; a perpendicular offset is set by the 3-4-5 method or an optical square; the offset length is recorded with its chainage.

Leveling: reduced level RL = height of instrument (HI) − staff reading; HI = RL of benchmark + backsight; the rise-and-fall method records backsight and foresight differences directly as rises or falls.

Contour interval depends on scale: 0.25–0.5 m for 1:500, 0.5–1 m for 1:2000, 1–2 m for 1:5000 and larger for reconnaissance maps; closer intervals show gentler landform detail.

Slope (%) = (vertical difference / horizontal distance) × 100; slope in degrees = arctan(V/H); a 1 in 10 slope equals 10% or about 5.7°.

Plane table surveying is used for small-scale watershed and farm maps; the three-point problem resolves the instrument station by resection using two known points and the intersection of rays.

Global positioning system and total station survey: total station records horizontal angle, vertical angle and slope distance, and computes coordinates and RL; accuracy is expressed as ±(2 mm + 2 ppm).

Area computation: trapezoidal rule A = d[(O1 + On)/2 + O2 + … + O(n−1)] for equally spaced offsets; Simpson's rule requires an odd number of ordinates and is more accurate for curved boundaries.

Earthwork volume by the prismoidal formula V = (L/6)(A1 + 4Am + A2); the mean sectional area method V = L(A1 + A2)/2 is acceptable for short reaches with little change in section.

Map scale: a representative fraction of 1:5000 means 1 cm on the map equals 50 m on the ground; a contour crossing a stream forms a V pointing upstream, which identifies the drainage direction.

Tillage tools: mouldboard plough (inversion, primary tillage), disc plough (scouring in sticky soils), cultivator and harrow (secondary tillage), rotavator (combined primary and secondary tillage in one pass).

Draft of a tillage implement scales with soil resistance and width of cut; specific draft (N/cm²) increases with clay content and moisture at the plastic limit; tillage at field capacity minimizes draft.

Terraces and bunds are built with a bund former, ridger, or scraper; a laser land leveler reduces water use by 15–25% and improves uniformity of basin irrigation.

Check dam materials: gabion (wire mesh with boulders, flexible, permeable), loose boulder, brushwood, and masonry (rigid, requires a sound foundation and a spillway).

Farm pond and dugout construction: excavator or scraper for earthwork; the embankment must be compacted in 15–20 cm layers at optimum moisture and protected with a grass cover.

Spillway design: the surplus weir passes the design peak flow; the weir length L = Q/(C·H^1.5), with C about 1.7 for a broad-crested weir in SI units.

Safety and maintenance of tools: replace cracked handles, keep cutting edges sharp, guard the PTO shaft of a rotavator, and never clear a jammed implement with the engine running.

Conservation structures need an outlet: a bund without a safe outlet or a grassed waterway fails by breaching; the structure is designed for the runoff from its own catchment, not the whole watershed.

Measurement of implement performance: field capacity (ha/h) = (width in m × speed in km/h)/10 × field efficiency; field efficiency is typically 70–85% for tillage.

Cost estimation for a conservation work = quantity of earthwork × unit rate + material + labour + contingency (typically 5–10%); earthwork volume is computed from cross-sections, not from area alone.

A soil conservation enterprise can be a custom-hiring centre for laser levelers, rotavators and bund formers; break-even point = fixed cost / (selling price per unit − variable cost per unit).

Record keeping for a farm enterprise: input costs, labour days, machine hours, yield and price; gross margin = gross return − variable cost; net profit also deducts fixed costs.

Subsidy and credit routes for watershed and conservation works: bank term loans under agricultural schemes, watershed development programmes and cooperative credit; the beneficiary share is normally defined in the project guidelines.

Safety: pesticide handling requires gloves, mask and eye protection; observe the pre-harvest interval on the label; store chemicals away from food and water sources.

Environmental risks of soil conservation works: sediment trapping behind check dams can silt up storage, and runoff diversion can deprive downstream users; design must consider the whole catchment.

Contour ploughing across a steep slope can concentrate water in furrows and cause gully initiation; furrows must be graded to a safe outlet on slopes above about 2%.

Burning crop residue destroys organic matter and soil biology and is a major source of particulate pollution; residue retention or incorporation is the conservation alternative.

Waterlogging and salinity from over-irrigation are managed by drainage, gypsum for sodic soils, leaching of salts and a switch to tolerant crops; prevention costs less than reclamation.