UPHESC Assistant Professor Agronomy PYQs

Concept: USSL (Richards, 1954) classification uses EC_e (dS/m), ESP and pH.

1. Saline: EC > 4, ESP < 15, pH < 8.5.
2. Saline-alkali: EC > 4, ESP > 15.
3. Alkali (sodic): EC < 4, ESP > 15, pH > 8.5 – matches the question.

Short trick: High EC = saline; high ESP = alkali; both high = saline-alkali.

Concept: Saline soils contain excess neutral soluble salts – chlorides and sulphates of Na, Ca, Mg (white crust, 'white alkali', Solonchak).

1. Alkali soils have excess exchangeable Na and Na₂CO₃ (black alkali, Solonetz).
2. Acid soils have excess H⁺ and Al³⁺.

Short trick: Neutral salts → saline (white); Na on exchange complex → alkali (black).

Concept: Standard lime-requirement table (ground limestone to raise pH of the plough layer from 5.5 to 6.5): warm-temperate/tropical (warm humid) clay loam needs about 2.0 tons/acre ≈ 5.0 t/ha.

1. Lime need rises with clay and organic matter (higher buffer capacity): sand < loam < clay loam < muck.
2. Warm humid soils need less than cool-temperate soils of the same texture (kaolinitic clay, lower CEC).
3. 2 tons/acre × 2.5 ≈ 5 t/ha.

Short trick: Clay loam, warm humid, pH 5.5 → 6.5 ≈ 5 t/ha limestone.

Concept: Na⁺ is a large hydrated monovalent ion; it expands the diffuse double layer and disperses (deflocculates) clay.

1. Dispersed clay clogs pores → poor infiltration, poor aeration, hard surface crust.
2. Ca²⁺ (gypsum) does the opposite – flocculation.

Short trick: Na disperses, Ca flocculates – hence gypsum for sodic soils.

Concept: Saline soil: EC of saturation extract > 4 dS/m, ESP < 15, pH < 8.5.

1. EC < 4 dS/m is the normal/sodic range.
2. 3.0 and 2.0 dS/m are below the salinity limit.

Short trick: Saline = 'more than 4'.

Concept: Salinity of irrigation water is caused by neutral soluble salts, chiefly chlorides (and sulphates) of Na, Ca and Mg; high Cl^- water raises soil EC.

1. Excess sodium (high SAR/RSC) causes sodicity (alkali soil), not salinity.
2. Calcium is the ameliorant; phosphorus is not a salinity factor.

Short trick: Chloride → salinity; Sodium → sodicity; Carbonate/bicarbonate → RSC.

Concept: Active acidity = H⁺ and Al³⁺ in the soil solution; it is what pH measures.

1. Exchangeable (salt-replaceable) acidity – H/Al held on exchange sites.
2. Reserve (residual) acidity – bound in OM/clay; Total = active + exchangeable + reserve.

Short trick: Solution = active; colloid surface = exchangeable/reserve.

Concept: Meteorological drought (IMD): seasonal rainfall deficient by more than 25% of the normal (long-period average).

1. Deficit 26–50% = moderate, >50% = severe.
2. Hydrological – depletion of surface/ground water; Agricultural – soil moisture insufficient for crop.

Short trick: Rain deficit → meteorological; reservoirs → hydrological; crop → agricultural.

Concept: The moisture index (Thornthwaite's index, used by Krishnan for delineating India's dry-farming/climatic zones) is $\mathrm{MI}=\frac{P-PE}{PE}\times 100$, where P = precipitation and PE = potential evapotranspiration.

1. Every printed option, in both languages, has the product P × PE (or only PE) in the numerator – none has the difference P − PE.
2. Option (A) would be correct only if its '×' were read as '−'; as printed, $\frac{P\times PE}{PE}\times 100$ simply equals 100P, which is not a moisture index. (B) equals 100PE, (C) and (D) are dimensionally meaningless as an index.
3. So no option is correct as printed and the question is treated as a bonus.

Short trick: MI = (P − PE)/PE × 100 – water surplus or deficit as % of demand; negative = dry (arid < −66.7).

Concept: Specific heat (cal g^-1 °C^-1): water 1.0, organic matter (humus) ≈ 0.5, dry mineral soil ≈ 0.2.

1. So humus-rich and wet soils warm up slowly.
2. 0.2 is the value for mineral soil, 1.0 for water.

Short trick: Water 1 : humus ½ : mineral soil ⅕.

Concept: Light compensation point: light intensity at which gross photosynthesis = respiration, so net CO₂ exchange is zero.

1. Saturation point – intensity beyond which photosynthesis no longer rises.
2. Shade plants have low compensation points.

Short trick: Compensation = 'balance' (P = R); Saturation = 'no more rise'.

Concept: CAM plants open stomata at night and close them by day, giving the highest water-use efficiency.

1. Transpiration ratio: CAM ≈ 50–100, C₄ ≈ 250–350, C₃ ≈ 450–950 g water/g DM.
2. Examples: pineapple, agave, cacti.

Short trick: CAM = night-shift stomata = desert survivors.

Concept: Broad Bed and Furrow (BBF), developed at ICRISAT, is meant for deep Vertisols (black soils).

1. Beds ~1.0 m wide with 0.5 m furrows on 0.4–0.8% grade drain excess water safely and conserve moisture.
2. Black soils have low infiltration when wet, so surface drainage is essential.

Short trick: BBF – ICRISAT – Black cotton soil.

Concept: Abscisic acid (ABA), the 'stress hormone', is synthesised in roots under drying soil and signals stomatal closure.

1. Betaine is an osmolyte (osmotic adjustment), not the sensor/signal.
2. Cytokinin declines under stress; ethylene is mainly a ripening/senescence hormone.

Short trick: ABA = Anti-transpirant Big Alarm – closes stomata.

Concept: Neutron moisture meter: fast neutrons from Am-Be source are slowed by hydrogen of soil water; counts of slow neutrons give volumetric moisture in situ, repeatedly at the same spot.

1. Gravimetric – standard but destructive, not in situ.
2. Tensiometer and gypsum blocks measure tension/resistance and need calibration; limited range.

Short trick: Hydrogen slows neutrons → neutron probe = advanced in-situ method (TDR is newer still).

Concept: ${\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6+6{\mathrm{O}}_2\to 6{\mathrm{CO}}_2+6{\mathrm{H}}_2\mathrm{O}$, ΔG ≈ −686 kcal per mole (≈ 2870 kJ).

1. About 38 ATP (×7.3 kcal ≈ 277 kcal) are conserved – ~40% efficiency.
2. The rest is lost as heat.

Short trick: Glucose = 686 kcal = 38 ATP.

Concept: Conveyance efficiency $E_c=\frac{W_f}{W_d}\times 100$ (water reaching field ÷ water delivered at source).

1. $E_c=\frac{3,60,000}{5,00,000}\times 100$
2. = 0.72 × 100 = 72%.
3. 28% is lost in seepage/evaporation in the channels.

Short trick: Conveyance = received ÷ released.

Concept: Percolation: downward movement of water through saturated soil under gravity, below the root zone.

1. Infiltration – entry of water into the soil surface.
2. Seepage – lateral/downward loss from channels; Interflow – lateral subsurface flow.

Short trick: Infiltration = entry; Percolation = going deeper.

Concept: Drip systems are low-pressure systems working at about 1–3 kg/cm² (≈ 15–45 psi) at the head, against 2.5–5 kg/cm² for sprinklers.

1. 1 kg/cm² ≈ 14.2 psi, so 1–3 kg/cm² ≈ 14–43 psi.
2. Pressure-compensating emitters work within this range.

Short trick: Drip ≈ 1–3 bar ≈ 15–45 psi.

Concept: Fisher's rule of thumb: an experiment should have at least 12 error degrees of freedom for a reliable estimate of error.

1. In RBD error df = (t − 1)(r − 1).
2. E.g. 4 treatments need at least 5 replications: 3 × 4 = 12.

Short trick: Error df ≥ 12 decides the minimum replications.