Soil Fertility
Essential plant nutrients, deficiency and toxicity symptoms, NPK fertilizers, secondary and micronutrient management, soil testing and fertilizer recommendations, integrated nutrient management practices.
Frequently Asked Questions
What is Liebig's Law of Minimum and why is it important for exams?
Liebig's Law of Minimum states that plant growth is limited by the scarcest essential nutrient, not by the total amount of resources available. Even if all other nutrients are abundant, the plant will only grow as fast as the most deficient nutrient allows. For exams: this principle underpins soil testing and fertilizer recommendations — you must correct the limiting nutrient first.
What are the nutrient percentages in common fertilizers?
Key fertilizer compositions tested in exams: Urea — 46% N (highest N content among solid fertilizers). DAP (Di-Ammonium Phosphate) — 18% N + 46% P₂O₅. MOP (Muriate of Potash) — 60% K₂O. SSP (Single Super Phosphate) — 16% P₂O₅ + 12% S. CAN (Calcium Ammonium Nitrate) — 25% N. Ammonium Sulphate — 20.6% N + 24% S.
What are the critical levels for major nutrients in soil?
Critical nutrient levels below which crops show deficiency: N < 280 kg/ha (low), P < 10 kg/ha (Olsen P < 10 ppm), K < 150 kg/ha. For micronutrients: Zn < 0.6 ppm (DTPA-extractable), B < 0.5 ppm, Fe < 4.5 ppm, Mn < 2.0 ppm, Cu < 0.2 ppm. Zinc deficiency is the most widespread micronutrient deficiency in Indian soils.
What is the difference between soil fertility and soil productivity?
Soil fertility is the inherent capacity of soil to supply essential nutrients in adequate amounts and proper balance for plant growth. Soil productivity is the capacity of soil to produce a crop of specified quality under a defined set of management practices. A fertile soil may not be productive (e.g., waterlogged fertile soil) and a productive soil may not be naturally fertile (e.g., soils with heavy fertilizer inputs).
What is INM (Integrated Nutrient Management) and what exams test it?
INM is the combined use of chemical fertilizers, organic manures, and biofertilizers to maintain soil health and meet crop nutrient requirements sustainably. Key principles: use minimum chemical fertilizer, substitute 25–50% N through organic sources, apply biofertilizers for N fixation and P solubilization. Heavily tested in IBPS AFO, NABARD Grade A, ICAR JRF, and state PSC Agriculture Officer exams.
Which nutrient deficiencies show symptoms in which plant part?
Mobile nutrients (N, P, K, Mg) show deficiency in older/lower leaves first — the plant remobilizes these to new growth. Immobile nutrients (Ca, S, Fe, Zn, B, Cu, Mn) show deficiency in new/young leaves first — the plant cannot remobilize them. Key examples: N deficiency = yellowing from lower leaves upward; Fe deficiency = interveinal chlorosis on young leaves; Ca deficiency = tip burn on youngest leaves.