CUET Agriculture cheat sheet

CUET Agriculture: Core Agronomy and Soil Science

• Law of Minimum (Liebig): crop yield is limited by the nutrient in shortest supply relative to need; adding other nutrients does not raise yield until that deficit is corrected.

• Soil pH ranges: strongly acid <5.5, moderately acid 5.5-6.5, neutral 6.6-7.3, alkaline 7.4-8.4, strongly alkaline >8.5; most field crops perform best at pH 6.0-7.5.

• Cation exchange capacity (CEC) in cmol(+)/kg: sandy soils <5, loams 10-20, clay and organic soils >25; higher CEC means greater nutrient-holding capacity and slower leaching.

• Essential macronutrients from soil: N, P, K, Ca, Mg, S; micronutrients: Fe, Mn, Zn, Cu, B, Mo, Cl, Ni; C, H, O come mainly from air and water.

• Nitrogen fixation: Rhizobium forms nodules on legumes (symbiotic); Azotobacter and Azospirillum are free-living; BGA (blue-green algae) and Azolla fix N in paddy fields.

• Critical period for irrigation: flowering and grain/fruit filling are most sensitive to water deficit; avoid irrigation at maturity to prevent lodging and quality loss.

• Seed rate formula: seed rate (kg/ha) = (plant population/ha × test weight in g) ÷ (1000 × germination % × purity % × field establishment %).

• Crop rotation rule: alternate deep-rooted with shallow-rooted crops and legume with non-legume; avoid growing crops of the same family in consecutive seasons to break pest and disease cycles.

• Weed control: pre-emergence herbicides (e.g., pendimethalin, atrazine) act before weed emergence; post-emergence herbicides (e.g., 2,4-D, glyphosate) act on emerged weeds; rotate herbicide modes of action to delay resistance.