Sub Irrigation, also known as Seepage Irrigation, is a method of irrigation in which water is delivered to the plant root zone from below the soil surface and absorbed upwards. The excess can be collected and reused. Sub-irrigation is rarely used in irrigated arid or semi-arid areas, where irrigation is frequently required to germinate crops. It is usually combined with subsurface drainage or controlled drainage. In this article, we will discuss Sub Irrigation or Seepage Irrigation which will be helpful for UPSC exam preparation.

What is Sub Irrigation or Seepage Irrigation?

• Watering from below the root zone, also known as seepage irrigation, is a method of delivering water to plants by controlling the level of the water.
• It is an effective method of water conservation with low labour requirements once the system is installed.
• Sub-irrigation in agricultural fields is accomplished by causing the water table to rise or fall.
• However, unlike flood or furrow irrigation systems, sub-irrigation does not flood the field up to the ground level.
• As a result, sub-irrigation is not commonly found in arid or semi-arid systems because sufficient moisture is required to germinate seeds at the surface level.
• In fact, areas that require high levels of drainage to be farmable are ideal candidates for a sub-irrigation system because the same network of drainage pipes and tiles that are installed to move excess water out of the ground can also be repurposed to add water when plant growth necessitates irrigation.
• Sub-irrigation is accomplished in controlled environmental agriculture (CEA) systems, such as commercial greenhouses for crop or horticulture production, by placing potted plants in a managed water reservoir and allowing capillary action to pull water up into the plant's soil and root system.
• Sub irrigation is used to grow field crops such as tomatoes, peppers, and sugarcane in areas with high water tables.
• For potted plants in greenhouses, three basic types of sub-irrigation systems are in use:
  • ebb-and-flow (bench-mounted enclosures holding pots are filled and then drained);
  • trough (water flows through bench-mounted, slightly sloping enclosures containing pots); and
  • flooded floor (special sloped concrete flooring is flooded and drained).

Types of Sub-irrigation Systems

Trough System

• Potted plants are installed along the edge of a plastic or metal trough that has a very slight slope from one end to the other.
• Water, often containing a nutrient solution, is pumped into the trough and flows down its length, aided by gravity. The pots absorb moisture from the trough.
• The water is captured for reuse and recycled back through the system at the bottom of the trough.

Ebb and Flow Benches

• Ebb and flow bench systems combine a greenhouse benching design with sub-irrigation methods to efficiently hold potted nursery plants.
• Water and usually a nutrient solution are pumped into channels in the bottom of 4' to 6' wide watertight benches.
• The benches can be installed in either fixed or movable configurations.
• The nutrient solution is pumped into the solutions and allowed to absorb by the potting medium before being drained, captured, and recycled for future use.

Flood Floors

• Flood floors are similar to the ebb and flow benches, but the entire system is built on a watertight concrete floor rather than benches. On the floor are potted plants.
• Slotted PVC pipes are installed in the middle of the floor to funnel water and nutrient solution from large holding tanks onto the floor, after which a valve is flipped and the water is drained back into the holding tanks to be reused after a set period of time allowing the plants to wick up the moisture.
• The floor must be smooth so that water does not pool in any areas and can drain completely.

Advantages of Sub Irrigation

• Conserves water and nutrients: Sub-irrigation is a highly resource-efficient system, particularly in commercial greenhouse operations where water and nutrient solutions can be easily captured and stored for reuse.
• It depends on the type of sub-irrigation method used in field cropping, but there are design solutions for capturing sub-irrigation water run-off even in a field cropping system.
• Reduces Labor Costs: Sub-irrigation methods are very labour efficient once a system is in place.
• They usually only need to monitor the below-ground moisture level, which can be done remotely using soil moisture sensors, opening and closing drainage tiles, and possibly turning pumps on and off.
• Used as Drainage System: Farmers in areas where drainage tiles and pipes must be installed before planting can use drainage systems as a sub-irrigation system.

Disadvantages of Sub Irrigation

• Requires Uniform Soil Types and Level Fields: For successful sub-irrigation, uniformity is essential.
• Sloped fields or fields with different types of soil will affect water permeability and capillary rising, causing the water table to rise either too high or not high enough for effective sub-irrigation.
• Salt Buildup: Depending on the method of sub-irrigation used, it can result in an unhealthy salt buildup in the topsoil. As a result, water with a high salt content should be avoided.
• Requires Adequate Water Supply: Even if sub-irrigation is designed to capture and reuse water, a grower still needs enough water to effectively inject into the soil and raise the water table.
• As a result, if farmers have limited access to irrigation water, sub-irrigation may not be an option.
• Potential issues, such as the increased presence of disease in recycled water.
• One of the challenges is to keep the water table just below the root zone so that the crop gets enough soil moisture to meet evapotranspiration requirements while avoiding root zone saturation, which can harm the crop.

Conclusion

A sub-irrigation system can be useful for watering field crops as well as controlled environments such as plant nurseries, commercial greenhouses, and even hydroponic systems. However, soil type and permeability, water table, and climatic conditions must be uniquely suited to support a sub-irrigation system, particularly in outdoor cropping systems. Even when they do, designing and managing an optimised sub-irrigation system can be difficult.

FAQs

Question. What is Sub-Irrigation or Seepage Irrigation?

Question. Where is Sub-Irrigation commonly used?

Question. What are the types of Sub-Irrigation systems?

Question. What are the advantages of Sub-Irrigation?

Question. What are the challenges associated with Sub-Irrigation?

MCQs

1. What is the main benefit of Sub-Irrigation?

A) Increased crop yields

B) Reduced labor costs and water conservation

C) Improved soil fertility

D) Requires no maintenance

2. Which of the following methods is commonly used in Sub-Irrigation?

A) Sprinkler systems

B) Drip irrigation

C) Ebb and flow benches

D) Surface flooding

3. What is required for effective Sub-Irrigation?

A) High salt content in water

B) Uniform soil and flat terrain

C) Low water tables

D) Frequent irrigation schedules

4. Which of the following is a disadvantage of Sub-Irrigation?

A) Increased soil erosion

B) Requires a high water supply

C) Salt buildup in the topsoil

D) Increased manual labor

5. Which of the following crops can benefit from Sub-Irrigation?

A) Wheat

B) Rice

C) Tomatoes

D) Barley

GS Mains Questions and Model Answers

Q1: Explain the concept and advantages of Sub-Irrigation for sustainable agriculture.

Answer: Sub-Irrigation offers a sustainable way to irrigate crops, especially in areas with high water tables or in controlled environments like greenhouses. By conserving water and nutrients, it helps reduce resource wastage. The method is highly efficient, requiring minimal labor for maintenance. It also prevents waterlogging and ensures deep water penetration to plant roots, promoting healthy crop growth.

Q2: What are the potential environmental and economic impacts of Sub-Irrigation?

Answer: Sub-Irrigation can have positive environmental impacts by reducing the need for excessive water usage and minimizing water runoff. It can also improve crop yields in arid areas, contributing to economic sustainability. However, it requires an adequate water supply and the right soil conditions. Additionally, improper use can lead to salt buildup in the soil, which could degrade soil quality over time.

Q3: How can Sub-Irrigation be improved for use in different climatic regions?

Answer: To optimize Sub-Irrigation in diverse climates, adjustments in system design are necessary. In arid climates, techniques like nutrient recycling and precise water management should be used to avoid water scarcity. In tropical regions, ensuring proper drainage to prevent waterlogging is critical. Research into more efficient water delivery methods and soil treatments can help tailor this system to various regions.

Previous Year Questions on Sub-Irrigation

1. UPSC CSE 2017

Question: "Discuss the significance of modern irrigation systems in enhancing agricultural productivity in India."

Answer: Modern irrigation systems like drip and Sub-Irrigation improve agricultural productivity by optimizing water use and reducing waste. Efficient irrigation is crucial in India, where water scarcity and uneven rainfall affect crop yields, making water management techniques vital for sustainable farming.

2. UPSC CSE 2019

Question: "Examine the challenges and benefits of water conservation techniques in Indian agriculture."

Answer: Water conservation techniques like Sub-Irrigation, rainwater harvesting, and drip irrigation are essential for addressing India’s water crisis. These methods help conserve water, improve crop yield, and reduce costs, though challenges like the initial investment, infrastructure needs, and climatic variability must be addressed for broader implementation.