৪৯তম বিসিএস ⎯ কৃষিবিজ্ঞান [৮০১]

Essentiality of Nutrient:
- Can't complete its life cycle in absence of the element
- Can’t be replaced by another element.
- It directly participates in plant metabolism.

Zinc is required for the synthesis of tryptophan, a precursor of auxin (Indole-3-acetic acid, IAA). Auxins regulate cell elongation and plant growth. 
​Interveinal chlorosis is not a function but a symptom of Zn deficiency (seen in young leaves).
​Component of chlorophyll is the role of Magnesium (Mg), not Zinc.

Urea - Urea is a fertilizer form; it must first be hydrolyzed by soil enzymes into NH₄⁺ before plants can use it.
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​N₂ gas- Atmospheric nitrogen cannot be used directly by most plants. Only nitrogen-fixing bacteria can convert it into usable forms.
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NH₄⁺ and NO₃^⁻ - Plants absorb nitrogen mainly as ammonium (NH₄⁺) or nitrate (NO₃⁻) ions from the soil. These are soluble and readily available for metabolism.

NO₂^- - Nitrite is usually an intermediate in the nitrogen cycle and toxic to plants in high amounts.

Compost is a decomposed organic matter that serves as a rich soil amendment including nitrogen (N), phosphorus (P), and potassium (K), as well as essential micronutrients.

Urea is a synthetic organic compound primarily used as a nitrogen (N) fertilizer.

Muriate of Potash is a common name for potassium chloride (KCl), a salt used as a potassium (K) fertilizer. 
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Ammonium Nitrate is a chemical fertilizer that supplies nitrogen (N) in two different forms: ammonium and nitrate. Both are contain N 

Ammonium Nitrate: Contains about 33–34% N.

Ammonium Sulphate: Contains about 21% N.

Diammonium Phosphate (DAP): Contains about 18% N and 46% P₂O₅.

Urea: Contains about 46% N, which is the highest nitrogen content.

A starter solution is a dilute solution of fertilizers containing N, P, K in the ratio of 1:2:1 or 1:1:2, applied to transplanted seedlings at the time of planting.

​Purpose / Use

To help seedlings establish quickly after transplanting.
Supplies readily available N, P, K near the root zone.
Reduces transplanting shock.
Ensures quick early growth of crops.
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​Advantages

Quick and effective nutrient supply.
Better root development.
Improved crop stand in early growth.
Reduces nutrient loss compared to broadcasting.

Limitations

Only suitable for transplanted crops.
Supplies only a small part of total crop nutrient requirement.
Preparation and handling require more care.

(Antagonism: Excess of one nutrient reduces the uptake, availability, or utilization of another nutrient.).
Excess phosphorus reduces the uptake and utilization of zinc (Zn), leading to zinc deficiency in plants.
This is one of the most common examples of nutrient antagonism in crop nutrition.
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​Antagonistic Nutrient Pairs

Phosphorus (P) ↔ Zinc (Zn) = Excess P reduces Zn uptake → Zn deficiency.
Potassium (K) ↔ Magnesium (Mg
Calcium (Ca) ↔ Magnesium (Mg)
Sulphur (S) ↔ Molybdenum (Mo)
Nitrogen (N) ↔ Sulphur (S)
Iron (Fe) ↔ Manganese (Mn)
Copper (Cu) ↔ Molybdenum (Mo)

Zn deficiency produces whitish streaks on leaves and the young central leaves become almost white — this is called white bud symptom, a classic indicator of Maize. 
​Bronzing of leaves: Related to Zinc toxicity or sometimes Iron deficiency.
​Stunted ear development is the symptom of Boron deficiency in maize
Rolling of leaves is the common symptom of water stress or drought, not zinc deficiency.

Broadcasting : Spreading fertilizers uniformly over the soil surface; it is simple and cheap but less efficient due to nutrient losses and uneven distribution.
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​Band placement: Fertilizer is placed in narrow bands near the plant roots to improve nutrient uptake.

Side dressing: Fertilizer is applied along the side of growing plants to meet nutrient requirements during critical growth stages.

Foliar application: Fertilizer is sprayed directly onto leaves for quick absorption.

Nitrogen is a primary macronutrient that plays a vital role in:
Protein and enzyme synthesis (for cell growth and metabolism)
Chlorophyll formation (for photosynthesis)
Nucleic acids (DNA & RNA) (for cell division and elongation)
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When nitrogen is deficient:
Plants cannot synthesize enough proteins and chlorophyll.
Photosynthesis is reduced → less energy for growth.
Shoots become stunted and weak, with small pale-yellow leaves.
Roots may continue to grow slowly (sometimes relatively longer to search for nutrients), but shoot growth is more severely affected.

প্রশ্নটাতে একটু সমস্যা আছে। আসলে এখানে সবগুলো antagonism pair. তবে অপশন গুলোর মধ্যে বেশী appropriate হবে Ca and MG. কারণ এই দুটি খুবই সামান্য antagonism effect দেখায়। তাই অধিক গ্রহণযোগ্য উত্তর হিসেবে গ) Ca vs Mg সঠিক উত্তর রাখা হয়েছে। 

(Antagonism: Excess of one nutrient reduces the uptake, availability, or utilization of another nutrient.).
Excess phosphorus reduces the uptake and utilization of zinc (Zn), leading to zinc deficiency in plants.
This is one of the most common examples of nutrient antagonism in crop nutrition.
​
​Antagonistic Nutrient Pairs

Phosphorus (P) ↔ Zinc (Zn) = Excess P reduces Zn uptake → Zn deficiency.
Potassium (K) ↔ Magnesium (Mg
Calcium (Ca) ↔ Magnesium (Mg)
Sulphur (S) ↔ Molybdenum (Mo)
Nitrogen (N) ↔ Sulphur (S)
Iron (Fe) ↔ Manganese (Mn)
Copper (Cu) ↔ Molybdenum (Mo)

Potassium Functions:
1. Activates many enzymes.
2. Regulates stomatal opening and closing.
3. Enhances fruit size, quality, sugar, and starch accumulation.
4. Protein production and tuber development enhanced.
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​When K⁺ enters guard cells → water follows osmotically → guard cells swell → stomata open.

When K⁺ exits → water leaves guard cells → stomata close.

Basal application: Basal application is the practice of applying fertilizer to the soil before or at the time of planting. Seeds or seedlings can access nutrient immediately for strong early growth

Molybdenum (Mo) Deficiency Symptoms
​Whiptail in cauliflower → leaf blades do not develop properly,
• Stunted growth due to poor nitrogen utilization.
• Poor nodulation in legumes → reduced nitrogen fixation.
• Marginal scorching of older leaves in severe cases.

Chlorosis of younger leaves first: This is a symptom of a deficiency in an immobile nutrient, such as iron, zinc, or calcium.
Necrosis of leaf tips only: While nitrogen deficiency can lead to necrosis (tissue death), it's not typically limited to the leaf tips.
Wilting of roots: Wilting is usually a sign of dehydration or root damage, not a nutrient deficiency.

​So the correct answer is Chlorosis of older leaves first.

The Integrated Nutrient Management principle is known as the 4R Nutrient Stewardship:

Right Source: Use the appropriate fertilizer or nutrient source.

Right Rate: Apply the correct amount according to crop needs.

Right Time: Apply at the crop’s critical growth stages.

Right Place: Place nutrients where roots can efficiently access them.

Purpose: Maximize nutrient use efficiency, increase yield, and reduce environmental impact.

Functions of Phosphorus (P):
1. Promotes root development and seed formation.
2. Increases flowering and fruiting.
3. Improves drought and disease resistance.
4. Legumes- helps to stimulate rhizobial activity and nodule formation.
5. Cereals- increase the strength of straw to prevent lodging.
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​Phosphorus is a key component of ATP, ADP, AMP, nucleic acids, and phospholipids.
It is directly involved in energy transfer, storage, and utilization inside plant cells.

Alkaline soils (high pH) increase ammonia volatilization from surface-applied nitrogen fertilizers like urea.
Deep placement involves placing fertilizer below the soil surface, near the root zone. This reduces contact with the air, minimizes nitrogen loss, and improves nutrient use efficiency.

Color change upper leaves (terminal bud dies)- Ca, B.
Color change upper leaves (terminal bud remain alive)- S, Fe, Mn, Cu, Mo, Cl.
Color change in lower leaves- N, P, K , Mg.

Rhizobium lives symbiotically in the root nodules of leguminous plants and fixes atmospheric nitrogen into ammonia.
​Azotobactor independently fixation Nitrogen. They don't produce nodule. 

Toxicity of Nitrogen:
1. Excessive vegetative growth, delayed flowering and maturity.
2. Lodging of cereals (weak stems).
3. Reduced uptake of P and K.
4. Increased susceptibility to diseases.

Deficiency of Boron:
1. Death of growing points (apical meristem necrosis).
2. Thick, brittle, cracked leaves.
3. Hollow stem in cauliflower, internal cork in apple, brown heart in sugar beet.
4. Poor pollination

Sodium nitrate (NaNO₃) and Calcium nitrate [Ca(NO₃)₂] supply nitrate (NO₃⁻) as the nitrogen form.
Along with nitrate, they release basic cations (Na⁺ or Ca²⁺) into the soil.
These cations neutralize soil acidity and make the soil reaction more alkaline (basic).
That’s why sodium nitrate and calcium nitrate are classified as basic fertilizers.

Ammonium sulphate → acidic fertilizer (produces H⁺ during nitrification).

Sodium nitrate & Calcium nitrate → basic fertilizers (supply Na⁺ or Ca²⁺, neutralize acidity).

Urea → considered neutral fertilizer in its immediate effect. When first applied, it is neutral.
But after hydrolysis and nitrification, it may slightly acidify the soil in the long term.

Plants absorb nutrients from the-
​Atmosphere → CO₂ (C), O₂
Water → H, O
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​Soil - The remaining nutrients. 
​Plants uptake the Nitrogen from the soil as ionic form. 

Muriate of potash (MoP) is the most widely used potassic fertilizer.
It contains about 60–62% K₂O and is chemically KCl (potassium chloride).

Sulfate of potash (K₂SO₄) → for chloride-sensitive crops.

Potassium nitrate (KNO₃) → supplies both K and N.

​​Rice requires alluvial, fertile, and high-water zones like the Ganges Floodplain

​Coastal plains near the Bay of Bengal have saline soils, suitable for salt-tolerant crops like certain rice varieties.

Khaira disease is Caused by Zn deficiency in rice. Plants show brown patches on leaves, stunted growth, reduced tillering.

Blast: A fungal disease caused by Pyricularia oryzae.

Tundu disease: A bacterial–nematode complex disease of wheat, not rice.

Brown spot: A fungal disease in rice caused by Bipolaris oryzae.

Essential element is 17. They are C, O, H, N, P, K Ca, Mg, S, Fe, Cu, Zn, Mn, Mo, Co, B, Cl. 
​So Aluminum is the correct answer. 
10 elements are Macro and 7 elements are micro .