Soil Fertility and Plant Nutrition
Soil Fertility and Plant Nutrition
This domain tests the 17 essential elements, their functions, deficiency symptoms, and fertilizer calculations. Odisha questions often involve urea, DAP, MOP, soil-test-based recommendations, and the difference between nutrient and fertilizer grades.
Core rules and concepts
- Essential elements: carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, sulphur, iron, manganese, zinc, copper, boron, molybdenum, chlorine and nickel. The first nine are needed in larger amounts; the rest are micronutrients.
- Nitrogen promotes vegetative growth and is mobile in the plant, so deficiency appears first in older leaves. Phosphorus supports root development and energy transfer. Potassium regulates water relations and enzyme activity.
- A fertilizer grade such as 46-0-0 means 46% N, 0% P₂O₅ and 0% K₂O. Urea is 46% N; DAP is about 18% N and 46% P₂O₅; MOP is about 60% K₂O.
- Soil testing avoids blanket doses; split nitrogen application improves recovery and reduces losses.
Worked example
A recommendation is 80 kg N/ha for 1.5 ha. Total N needed = 80 × 1.5 = 120 kg N. Urea contains 46% N, so urea required = 120 ÷ 0.46 = 260.9 kg. The reasoning is to multiply the per-hectare dose by area, then divide by the nutrient fraction in the fertilizer.
Traps that cost marks
Do not treat 80 kg N/ha as 80 kg urea/ha. Do not add P₂O₅ and P as if they were the same; P₂O₅ × 0.44 gives P. Luxury consumption is excess nutrient uptake without yield increase, not a deficiency. Organic manures release nutrients slowly, so their immediate effect is smaller than their total nutrient content suggests.