Irrigation Principles:

1. Water Requirement: This principle focuses on determining the water requirement of crops and ensuring an adequate water supply. It involves assessing factors such as crop type, stage of growth, soil type, climate, and evapotranspiration rates.

2. Water Distribution: The principle of water distribution aims to evenly distribute water throughout the field. It involves techniques such as furrow irrigation, sprinkler irrigation, drip irrigation, and surface irrigation. The choice of technique depends on factors like crop type, soil type, topography, and water availability.

3. Water Application Efficiency: This principle emphasizes using irrigation methods that maximize water application efficiency. It involves minimizing water losses due to evaporation, deep percolation, runoff, and wind drift. Improving irrigation efficiency helps conserve water resources and reduces costs.

4. Controlled Water Application: The principle of controlled water application involves applying water in controlled amounts and at the right time. It includes techniques like scheduling irrigation based on crop needs, using moisture sensors, and employing automation systems. Controlled irrigation helps prevent waterlogging and reduces the risk of crop diseases.

Drainage Principles:

1. Subsurface Drainage: Subsurface drainage aims to remove excess water from the soil profile. It involves installing drain pipes or tiles below the ground surface to collect and carry away excess water. Subsurface drainage helps improve soil structure, reduces waterlogging, and promotes root growth.

2. Surface Drainage: Surface drainage focuses on removing excess water from the soil surface. It involves shaping the land to create slopes or channels that facilitate the flow of water away from the field. Surface drainage helps prevent soil erosion, waterlogging, and damage to crops.

3. Drainage System Design: The principle of drainage system design involves designing an efficient drainage network. Factors such as soil type, topography, rainfall patterns, and water table depth are considered for designing the layout, spacing, and depth of drainage channels or pipes.

4. Water Quality Management: Water quality management is an essential aspect of drainage. It involves monitoring and managing the quality of drained water to prevent contamination of water bodies and ensure environmental sustainability.

In conclusion, the optional subject covers various irrigation and drainage principles, including water requirement assessment, water distribution techniques, water application efficiency, controlled water application, subsurface and surface drainage, drainage system design, and water quality management. Understanding these principles is crucial for efficient water management in agriculture, preventing water-related issues, and optimizing crop production.