৪৯তম বিসিএস ⎯ কৃষিবিজ্ঞান [৮০১]

subsurface irrigation Merits:
1. Evaporation loss is minimum
2. Permanent and efficient method
3. No soil erosion and wastage of land
4. Loss nutrient is minimum

Soil salinization
Electrical Conductivity (EC) measures the total dissolved salts in water.
High EC indicates that water contains a large amount of salts, which can accumulate in the soil over time.
This leads to soil salinization, reducing soil fertility and affecting crop growth.

Note: Sodium toxicity and soil alkalinity are related but are measured by Sodium Adsorption Ratio (SAR) and bicarbonate concentration, not EC directly.

Why Uneven terrain, sandy soils is the correct answer?
Uneven Terrain: Sprinkler systems apply water from above, making them highly effective on slopes and undulating ground where gravity-fed surface irrigation methods are unsuitable.

Sandy Soils: These soils have a high infiltration rate and don't hold water well. Sprinklers can apply water at a low, controlled rate over a longer period, preventing runoff and allowing the sandy soil to absorb the moisture properly.

When a soil loses a significant amount of its moisture, the water films holding the soil particles together disappear. This causes the soil to shrink and pull apart, forming visible cracks on the surface. As the soil continues to dry, it can become loose and powdery. These are direct physical signs that the soil lacks sufficient water for plant growth.
High humidity and high air temperature are climatic factors that influence the rate of water loss from the soil and plants (evapotranspiration).
Leaf color change is a plant-based indicator of water stress.

Merits:
1. Increased Crop Yield
2. Most suitable in arid regions
3. Fertilizer and Nutrient Savings
Demerits:
1. Maintenance cost is high
2. Not suitable for field crops

Soil Water Potential:
✓ How tightly water is held in the soil and how easily plants can take it up.
✓ High potential → water is easy for plants to absorb.
✓ Low potential (more negative) → water is harder for plants to absorb.

Leaf water potential: It is a measure of how much water energy is inside a leaf, which shows how easily the plant can move water
from the soil to the leaves.
High (less negative) → leaf has plenty of water.
Low (more negative) → leaf is under water stress.

Loamy soils are generally suitable but sandy loam is considered optimal because of its balanced texture, which provides the ideal combination of drainage and water retention for a wide range of crops.

Loamy soil with an impermeable layer below the root zone for this sub-surface irrigation is suitable .

Objectives of Irrigation:
✓ To control harmful soil insects
✓ To hasten the decomposition of organic matter in soil
✓ To leach and wash out injurious salt from the soil
✓ To maintain the temperature and humidity of soil
✓ To supply water for the nutrition and growth of plant
✓ To remove the moisture deficit condition of plants

Free flooding (প্লাবন) irrigation: "Free flooding (প্লাবন)" is a type of surface irrigation where water is applied directly to the soil surface from ditches without much control over the flow. It's also known as "wild flooding" because the water is allowed to spread freely over the land.
✓ Water is applied in the furrows
✓ Usually one furrow between crop rows
✓ Water can be control during irrigation
✓ Example- row crops (potato, cabbage, cauliflower, brinjal, chilli, cotton, tomato, maize, sugarcane)

surface irrigation: Applying water to the soil surface by gravity flow. Water is delivered to the field and spreads over the land to infiltrate the soil.

Characteristics of surface irrigation
Water is distributed by the natural slope of the land using gravity.
Requires little mechanical equipment, making it relatively inexpensive.
Consumes more water compared to other irrigation methods.
Loss of water is high occurs through evaporation and seepage.
Commonly used for rice, wheat, sugarcane, cotton, and other field crops.

For surface irrigation water is flowed on soil surface and evaporation loss of water is high. 

pH less than 7 is Acidic
pH greater than 7 is Alkaline
PH =7 is neutral 

Soil Moisture Sensors are instruments that are directly inserted into the soil to measure its water content or the tension with which the soil holds water. This provides a direct and accurate reading of how much water is available for the plants.

Visual Indicators rely on observing the plant for signs of water stress (e.g., wilting), which is an indirect method and often indicates that stress has already occurred.

Evaporation Pan Method uses a pan of water to estimate potential evapotranspiration, which is an indirect way to calculate water loss, not a direct measure of soil moisture.

Calendar-Based Method is a fixed-schedule approach that does not account for actual soil moisture, relying instead on a predetermined watering frequency.

Drip irrigation
Also known as trickle and Micro-irrigation system
✓ Delivers water slowly and frequently through small diameter pipes
✓ Water is applied drop by drop to the root zone of a crop
✓ Example- grapevines, strawberry, vegetables, greenhouses

Objectives of irrigation scheduling 
1. Maximizing Water Use Efficiency
2. Preventing Crop Water Stress
3. Increasing Crop Yield and Quality
4. Minimizing Environmental Impact
5. Optimizing Energy and Labor Use

Importance of Drainage :
✓Control the loss of plant nutrients
✓ Enhance the activity of soil organism
✓ Improve soil structure
✓ Manage good aeration in the soil
✓ Prevent soil accumulation on surface soil

Maximum wastage of water is occurred in free flooding irrigation compere with others irrigation. 
Merits:
1. Large areas can be irrigated in a short time
2. Low-cost method that requires minimal labor and minimum wastage of land
3. Suitable for close-growing crops like Rice 
Demerits:
1. Cannot be used to irrigate uneven or high-low lands.
2. Soil erosion is high (Only 20% water is used by plants)
3. Lead to waterlogging (not suitable for water sensitive plants like spinach, broccoli 

Border strip irrigation Method
Merits:
1. Highly mechanized, suitable for large farms
2. Provides better water control
3. Higher application efficiency compared to free flooding
Demerits:
1. Required land grading and leveling, which can be costly
2. Not suitable for uneven and slope land
3. Labor intensive

Readily available water (RAW) is the portion of soil water that crops can easily extract between field capacity and the point where plants start to experience water stress.

Field capacity: The maximum water soil can hold after excess water has drained.

Permanent wilting point: The soil moisture level at which plants cannot recover even if water is added.

Saturation point: Soil is completely filled with water; no air spaces remain.

Sodium Adsorption Ratio (SAR) measures the proportion of sodium (Na⁺) relative to calcium (Ca²⁺) and magnesium (Mg²⁺) in water.
High SAR means excess sodium compared to calcium and magnesium.


Soil acidity: Related to H⁺ ions, not SAR.

Boron toxicity: Related to excess boron, not sodium.

Nutrient deficiency is  not directly measured by SAR.

Flooding and Basin Irrigation
Flooding and basin irrigation, while simple and inexpensive, are generally not recommended for most vegetable crops. These methods saturate the entire field, which can lead to:
Waterlogging, Nutrient Leaching, Disease Risk
Ring basin irrigation is used in the orchard . 

Sprinkler Irrigation
Sprinkler irrigation is especially for larger vegetable fields or crops planted close together, like leafy greens. It mimics rainfall, providing a uniform application of water over the entire field. While not as water-efficient as drip irrigation, modern sprinkler systems offer good control and can be automated to ensure consistent watering.

Surface irrigation is 5 types
Flooding, Furrow, Border strip, Ring basin, Corrugation

Trickle is the another name of sprinkle irrigation. '

The correct answer is b) Amount of dissolved salts.

Explanation
Total dissolved solids (TDS) is a measure of the combined content of all inorganic and organic substances dissolved in water in the form of molecules, ions, or granules. When we talk about TDS in the context of irrigation, it refers to the concentration of dissolved salts

Drip irrigation is highly effective for these conditions due to its unique features:

Uneven Land: Unlike basin or flood irrigation which require a flat surface, drip irrigation systems are not affected by the slope or contour of the land. They use pressure regulators to ensure a uniform flow of water to each emitter, regardless of elevation changes.

High-Value Crops: This method delivers water and nutrients directly to the root zone of each plant, which minimizes waste and maximizes efficiency. For high-value crops, this precision leads to higher yields, better quality, and significant savings on water and fertilizer costs.

Efficiency: Drip irrigation boasts the highest water use efficiency, often exceeding 90%. This is crucial for high-value crops where water conservation is essential for profitability.

Trickle is the another name of Drip irrigation. 
In Drip irrigation Water is applied drop by drop to the root zone of a crop
✓ Example- grapevines, strawberry, vegetables, greenhouses crops

Drainage 
Process of removing excess water from a specific area
✓ Control soil erosion
✓ Control the loss of plant nutrients
✓ Enhance the activity of soil organism
✓ Improve soil structure
✓ Manage good aeration in the soil
✓ Prevent soil accumulation on surface soil
✓ Two types i) surface drainage ii) sub-surface drainage

Main objective of irrigation scheduling
✓ Deciding when to irrigate
✓ How much water to apply to crops for optimal growth
✓ Necessary for agricultural production p

Corrugation irrigation is a variation of furrow irrigation
✓ Series of very small, shallow furrows or "corrugations" are created.
✓ Water flows down these narrow channels and spreads laterally to wet the soil between them.
✓ The method is primarily used for close-growing crops that are sown broadcast rather than in rows. (Wheat)

Water can be used if the water-bearing layer is within 6–8 meters of the surface because water at this depth can be easily lifted by wells or shallow tube wells. It requires less energy and cost, making it convenient for irrigation.
Less pressure on equipment – Pumps and wells work efficiently at this depth, while at deeper levels (50–100 m) more powerful and costly equipment is needed.