UPHESC Assistant Professor Agricultural Chemistry & Soil Science PYQs

Concept: In routine soil-testing flame photometers (LPG–air flame), the compressor air pressure for the atomiser is kept at about 0.4–0.6 kg cm^-2 (6–8 psi) for K and Na.

1. This gives a stable, non-luminous blue flame. Too high a pressure blows the flame off; too low a pressure gives poor aspiration.
2. K is read at 766–768 nm and Na at 589 nm.

Short trick: Flame photometer air: 0.4–0.6 kg/cm².

Concept: Jackson's tri-acid mixture for wet digestion of plant samples is HNO₃ : H₂SO₄ : HClO₄ = 10 : 1 : 4.

1. HNO₃ first oxidises the easily oxidised organic matter; HClO₄ completes the oxidation; a little H₂SO₄ raises the boiling point.
2. The digest is used for P, K, Ca, Mg, S and micronutrients. The di-acid mixture is HNO₃ : HClO₄ = 9 : 4.

Short trick: Tri-acid = 10 : 1 : 4 (nitric : sulphuric : perchloric).

Concept: ICP-OES uses an argon plasma (about 6,000–10,000 K) sustained by a radio-frequency induction coil.

1. Argon is inert, cheap and has a high ionisation energy, so it efficiently atomises and excites most elements.
2. Many elements can then be read at once from their emission lines.

Short trick: ICP torch = argon.

Concept: Bragg's law: $n\lambda =2d\sin \theta$. X-rays diffracted by crystal planes reinforce each other when this is satisfied.

1. An X-ray diffractometer measures θ and calculates the basal spacing d. For example, kaolinite is 0.72 nm, illite 1.0 nm, smectite 1.4–1.8 nm (glycolated) and chlorite 1.4 nm. This identifies clay minerals.
2. AAS works on atomic absorption; HPLC on chromatography; mass spectrometry on m/z separation.

Short trick: Bragg = $2d\sin \theta$, i.e. XRD.

Concept: Compare the K content of the pure compounds (K = 39.1).

1. K₂CO₃ (M = 138.2): 78.2 ÷ 138.2 = 56.6% K = 68% K₂O.
2. KCl (74.6): 52.4% K = 63% K₂O (commercial MOP 60% K₂O).
3. K₂SO₄ (174.3): 44.9% K = 54% K₂O (commercial SOP 48–50% K₂O).
4. KNO₃ (101.1): 38.7% K = 46% K₂O (commercial 44% K₂O).
5. So potassium carbonate (about 66–68% K₂O) has the most K. MOP is the richest common potash fertilizer, but it has less K than K₂CO₃.

Short trick: The lighter the partner anion (CO₃ is shared by 2 K), the higher the % K.

Concept: Barber's three mechanisms of nutrient supply to roots are root interception, mass flow and diffusion.

1. Diffusion supplies most of the P (about 90%) and K (about 75–80%), because their solution concentrations are low and they are strongly buffered.
2. N (NO₃⁻), S, Ca and Mg reach the root mainly by mass flow.

Short trick: Diffusion = P and K; mass flow = N, Ca, Mg, S.

Concept: Higher plants, especially hyperaccumulators, take up heavy metals from soil through their roots and store them in their shoots.

1. Examples: Thlaspi caerulescens (Zn, Cd), Brassica juncea (Pb, Cd, Cr), Alyssum (Ni), Pteris vittata (As).
2. This is the basis of phytoextraction, the most widely used phytoremediation technique for metal-contaminated soils.

Short trick: Phyto-extraction = higher plants accumulate metals.

Concept: Climate-smart agriculture practices are grouped as water-, energy-, nutrient-, carbon-, weather- and knowledge-smart.

1. Knowledge-smart practices include capacity development, ICT-based advisories, seed/fodder banks and new crop rotations or diversification.
2. Crop residue management (incorporation or retention instead of burning) is a carbon-smart practice, so it is not knowledge-smart.

Short trick: Residues are about soil carbon, so they are carbon-smart.

Concept: D.J.D. Nicholas (1961) proposed the term 'functional or metabolic nutrient': any element that functions in plant metabolism, whether or not its action is specific.

1. This broadened Arnon and Stout's (1939) strict criteria of essentiality.
2. E. Gris (1844) first showed that Fe is essential; de Saussure studied plant ash and the uptake of CO₂.

Short trick: Arnon = essential element; Nicholas = functional nutrient.

Concept: Doran and Zeiss (2000) wrote that the term 'soil health' portrays soil as a finite, non-renewable and dynamic living resource.

1. They defined soil health as the capacity of soil to function as a vital living system.
2. Karlen et al. (1997) and Doran and Parkin (1994) are associated with definitions of soil quality.

Short trick: 'Living resource' = Doran & Zeiss (2000).

Concept: Soil resilience (Lal, Szabolcs) is the ability of a soil to recover its functional and structural integrity after a disturbance.

1. Soil resistance is the ability to withstand change during the disturbance itself.
2. Soil quality is the capacity to function; soil productivity is the capacity to produce crops.

Short trick: Resist = not bend; Resilience = bounce back.

Concept: Humic and fulvic acids and other organic ligands form chelates (ring complexes) with Zn, Cu, Fe and Mn.

1. Chelation keeps the metals in a protected form that resists leaching and precipitation while still being available to roots.
2. Fixation reduces availability rather than conserving the nutrient in an available form.

Short trick: Chelate = 'claw' that holds the metal.

Concept: Glomalin is a sticky glycoprotein produced by arbuscular mycorrhizal fungi (Glomus).

1. Residue addition and reduced tillage favour AM fungi, so glomalin-related soil protein rises.
2. Glomalin glues micro-aggregates into water-stable macro-aggregates (>250 µm).

Short trick: Glomalin = 'super glue' of soil (from Glomus).

Concept: The Soil Health Card scheme was launched by the Prime Minister on 19 February 2015 at Suratgarh (Sri Ganganagar, Rajasthan).

1. Cards report 12 parameters (N, P, K, S, Zn, Fe, Cu, Mn, B, pH, EC, OC) with fertilizer recommendations, renewed every 2 years.
2. 5 December is World Soil Day; 19 February is observed as Soil Health Card Day.

Short trick: Suratgarh, 19-02-2015.

Concept: NBSS&LUP (Sehgal et al., 1990–92) divided India into 20 agro-ecological regions (AERs).

1. These were further divided into 60 agro-ecological sub-regions (AESRs) using soils, climate (length of growing period) and physiography.
2. The Planning Commission separately recognised 15 agro-climatic zones.

Short trick: 20 regions, 60 sub-regions (NBSS&LUP); 15 agro-climatic zones.

Concept: Watersheds are classified by size.

1. Macro > 50,000 ha; sub-watershed 10,000–50,000 ha; milli-watershed 1,000–10,000 ha; micro-watershed 100–1,000 ha; mini-watershed 1–100 ha.

Short trick: Milli = 1,000s of ha; Micro = 100s; Mini = below 100.

Concept: In the land capability classification (USDA, as adopted in India):

1. Class II has moderate and Class III severe limitations.
2. Class IV has very severe limitations: steep slopes, severe erosion (past or hazard), poor drainage, shallow soil. It can be cultivated only occasionally with intensive conservation.
3. Class V is nearly level, not erosion-prone, but too wet or stony for cultivation.

Short trick: Severe erosion + poor drainage = last arable class = IV.

Concept: Slope limits commonly used with land capability classes:

1. Class I: 0–1%; Class II: 1–3%; Class III: 3–8%; Class IV: 8–15%; Class VI: 15–35%; Class VII: 35–50%; Class VIII: >50%.
2. So Class IV has 8–15% slope.

Short trick: 1-3-8-15-35: classes II, III, IV, VI in order.

Concept: Land capability classes rest on permanent limitations: erosion (e), wetness or inundation (w), soil limitations such as salinity, depth and stoniness (s), and climate (c).

1. Saline, inundated and organic soils are placed in classes with s or w subclasses.
2. Low fertility is a correctable limitation (fertilizers and manures), so it is not a basis for capability classes.

Short trick: Correctable by fertilizer = ignored in LCC.

Concept: Watershed management as a national programme took shape in the Seventh Five Year Plan (1985–90).

1. NWDPRA (National Watershed Development Project for Rainfed Areas) was conceived in the Seventh Plan and launched in 1990–91.
2. Earlier schemes (soil conservation in river valley catchments 1962, DPAP 1973, DDP 1977) were area programmes, not a watershed programme as such.

Short trick: 7th Plan, then NWDPRA.