Plant Nutrition and Irrigation
Plant nutrition and irrigation connect nutrient supply to water management. The exam tests essential elements, deficiency symptoms, fertilizer placement, and irrigation scheduling.
Essential elements and deficiency
Seventeen elements are essential: C, H, O, N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu, B, Mo, Cl, Ni. Macronutrients are needed in larger amounts. Mobile nutrients (N, P, K, Mg) show deficiency first in older leaves; immobile nutrients (Ca, Fe, B, Mn) show it in young leaves. Nitrogen deficiency causes pale green leaves; phosphorus deficiency causes purplish leaves; potassium deficiency causes marginal scorch; iron deficiency causes interveinal chlorosis; zinc deficiency causes khaira in paddy; boron deficiency causes hollow stem and poor fruit set.
Irrigation scheduling
IW/CPE ratio compares irrigation water depth to cumulative pan evaporation. A ratio of 0.8 means irrigate when cumulative evaporation reaches irrigation depth ÷ 0.8. Drip irrigation wets the root zone and saves water; sprinkler irrigation suits close-growing crops. Critical stages include tillering and panicle initiation in paddy, tasselling in maize, and pegging in groundnut.
Worked example
Irrigation depth = 40 mm; IW/CPE = 0.8; pan evaporation = 5 mm/day. Cumulative evaporation needed = 40 ÷ 0.8 = 50 mm. Interval = 50 ÷ 5 = 10 days. If rainfall occurs, subtract effective rainfall before irrigating.
Traps that cost marks
Do not apply the mobile/immobile rule backwards. Iron chlorosis in high-pH soil is not corrected by adding nitrogen. Boron has a narrow safe range; over-application is toxic. Drip is not a substitute for proper scheduling.