Test: Irrigation Techniques & Water Requirement of Crops - 2 - Civil Engineering (CE) MCQ

• Definition of Available Moisture Content: Available moisture content in the root zone of a crop refers to the amount of water that is accessible to the plants for uptake through their roots.


• Depletion of Moisture Content: When the available moisture content in the root zone decreases below a certain threshold, it can lead to water stress in plants, affecting their growth and yield.


• Irrigation Warranted: Irrigation of a field is normally warranted when the available moisture content in the root zone is depleted by approximately 50%.


• Signs of Depletion: Signs that indicate the need for irrigation include wilting of plants, dry soil, and decreased crop productivity.


• Importance of Proper Irrigation: Proper irrigation is essential to ensure optimal growth and yield of crops, as water is a critical factor in plant development.

Therefore, the correct answer is D: 50%.

• Definition: Conjunctive use of water in a basin refers to the combined use of surface and groundwater resources within a specific geographic area.



• Surface water: This includes water from rivers, lakes, and reservoirs that can be used for irrigation, drinking water, industrial purposes, and hydropower generation.



• Groundwater: This refers to water stored beneath the earth's surface in aquifers, which can be accessed through wells and used for irrigation, drinking water, and other purposes.



• Benefits: By combining surface and groundwater resources, conjunctive use can help ensure a more reliable water supply, especially during times of drought or water scarcity. It also allows for more efficient water management and can help prevent over-extraction of groundwater resources.



• Challenges: However, there are challenges associated with conjunctive water use, such as the need for proper management to prevent depletion and contamination of groundwater sources, as well as potential conflicts over water rights and allocation.

Net Irrigation Requirement (N!R) is the amount of irrigation water required in order to meet the evapotranspiration need of the crop as well another, needs such as leaching. Therefore, NIR = C_u - R_e + Water lost as percolation in satisfying other needs such as teaching.

When a system of open jointed drains is artificially laid below the soil, so as to supply water to the crops by capillarity, then it is known as artificial sub-irrigation. It may be recommended only in some special cases with favourable soil conditions and for cash crops of high return.

• Contour Border Irrigation Method: This method involves dividing the land into border strips that are approximately on the contour of the land.


• Uniform Longitudinal Gradient: The border strips have a uniform longitudinal gradient, which helps in ensuring even distribution of water along the strip.


• Supply Ditch: In this method, the supply ditch runs along the contour of the land, providing water to the border strips.


• Efficient Water Distribution: By following the contour of the land and maintaining a uniform longitudinal gradient, water is distributed efficiently to the crops.


• Prevention of Water Wastage: Contour border irrigation helps in preventing water wastage by ensuring that water flows evenly across the border strips.

• Flow type: Spatially varied, unsteady, open channel flow


• Discharge: Decreasing along the border

• Spatially varied flow: In the border method of irrigation, the flow along the border is spatially varied as it varies in the lateral direction.


• Unsteady flow: The flow is unsteady because it changes with time due to the inflow and outflow dynamics of the irrigation water.


• Open channel flow: Since the water flows along the border of the field, it is an open channel flow as it is not confined within a pipe.


• Decreasing discharges: The discharges decrease along the border as the water spreads out and infiltrates into the soil, leading to a decrease in flow rate.

Therefore, the flow along the border in the border method of irrigation is a case of spatially varied, unsteady, open channel flow with decreasing discharges.

Check flooding is similar to ordinary flooding except that the water is controlled by surrounding the check area with low and flat levels. Levels are generally constructed along the continuous having vertical interval of about 5 to 10 cm. 
This method is suitable for more permeable soils as well as for less permeable soils. The water can also be held on the surface for a longer time in case of less permeable soils.

• Definition: Check basin irrigation is a method of applying water to the crops by creating small basins or checks around the plants.


• Efficiency: Check basin irrigation is highly efficient in water usage as it ensures that water is directly applied to the root zone of the plants.


• Water Conservation: This method helps in conserving water by reducing evaporation and runoff, as water is contained within the basins.


• Customization: Check basin irrigation allows for customization of water application based on the specific water needs of each plant.


• Reduces Weed Growth: By targeting water directly to the plant roots, check basin irrigation helps in reducing weed growth as water is not wasted on unwanted areas.


• Suitable for Paddy: Check basin irrigation is ideal for growing irrigated paddy as it ensures efficient water distribution and promotes healthy crop growth.

Factors that Limit the Maximum Application Rate by Sprinklers

• Infiltration capacity of the soil: The maximum application rate by sprinklers is limited by the ability of the soil to absorb water. If the application rate exceeds the infiltration capacity of the soil, water will run off, leading to water wastage and potential erosion.



 
• Prevailing wind velocity: High wind speeds can cause water droplets from sprinklers to drift away from the target area, reducing the effectiveness of irrigation. This limits the maximum application rate as the water may not reach the intended plants or crops.



 
• Quantity of water available: The maximum application rate by sprinklers is also limited by the amount of water that is available for irrigation. If there is a limited water supply, the application rate must be adjusted to ensure efficient use of water resources.



 
• Prevailing humidity and radiation: High humidity levels can lead to water loss through evaporation, while high radiation levels can increase water loss through evapotranspiration. These factors can limit the maximum application rate by sprinklers as the water may not effectively reach the plants or crops.


 

Therefore, it is important to consider these factors when determining the maximum application rate by sprinklers to ensure efficient and effective irrigation practices.

• No extra cost of land preparation is involved in sprinkler irrigation: This statement is correct because sprinkler irrigation does not require any additional land preparation like the construction of ditches or canals, unlike other forms of irrigation.


• Sprinklers can be used for the application of liquid fertilizers also: Sprinkler irrigation systems can be used to apply liquid fertilizers along with water, providing nutrients directly to the plants.


• Sprinkler irrigation is particularly advantageous in hilly terrains: Sprinkler irrigation is beneficial in hilly terrains where other forms of irrigation like surface or gravity irrigation may not be feasible due to the uneven terrain.

• Excessive soil erosion is initiated by sprinkler irrigation: This statement is incorrect as sprinkler irrigation actually helps in reducing soil erosion by evenly distributing water over the area, minimizing runoff and soil loss.

Therefore, the correct answer is option B, as excessive soil erosion is not initiated by sprinkler irrigation.