Irrigation Systems

• Irrigation refers to artificially applying water to land or soil.
• It aids in crop production, landscape maintenance, and revegetation of disturbed soils in dry regions or during insufficient rainfall.

Types of Irrigation Systems

• Surface Irrigation distributes water over the soil surface using gravity.
  • Flood Irrigation releases water to flow over the land, suitable for close-growing crops.
  • Furrow Irrigation applies water in small channels (furrows) between crop rows, efficient for row crops.
  • Border Irrigation divides land into strips with borders, applying water to each strip.
• Localized Irrigation applies water directly to the plant root zone.
  • Drip Irrigation uses small emitters for slow, frequent water application, minimizing water loss and maximizing efficiency.
  • Micro-Sprinkler Irrigation uses small sprinklers to apply water to a limited area around each plant.
• Sprinkler Irrigation sprays water into the air, allowing it to fall onto plants and soil.
  • Center Pivot Irrigation uses a pivoting arm with sprinklers to irrigate large circular areas.
  • Solid Set Irrigation involves fixed sprinklers placed throughout the field.
  • Traveling Gun Irrigation utilizes a large sprinkler that moves across the field.
• Subsurface Irrigation applies water below the soil surface.
  • This can be achieved by maintaining a high water table or using buried perforated pipes.

Irrigation Scheduling

• Irrigation scheduling is determining when and how much water crops need.
• The objective is efficient water application, maximizing crop yield while minimizing water waste.
• Methods include:
  • Soil Moisture Monitoring measures the amount of water in the soil.
    • Tensiometers measure soil water tension.
    • Soil Moisture Sensors are electronic devices that measure soil water content.
  • Plant Monitoring observes plant indicators of water stress.
    • Visual Inspection involves observing wilting, leaf color, and growth rate.
    • Infrared Thermometry measures leaf temperature.
    • Pressure Chamber measures leaf water potential.
  • Weather-Based Methods use weather data to estimate crop water use.
    • Evapotranspiration (ET) calculates water evaporated from the soil and transpired by plants.
    • Crop Coefficients adjust ET based on the specific crop and its growth stage.
  • Water Balance Approach tracks inputs (rainfall, irrigation) and outputs (ET, drainage) to determine when to irrigate.

Water Conservation Techniques

• Improving Irrigation Efficiency involves:
  • Using efficient irrigation systems like drip and micro-sprinkler irrigation.
  • Regularly maintaining irrigation systems to prevent leaks and ensure uniform water distribution.
  • Implementing irrigation scheduling based on crop water needs and soil moisture levels.
• Water Harvesting:
  • Collecting and storing rainwater for later use.
  • Constructing small dams or ponds to capture surface runoff.
• Soil Moisture Conservation:
  • Mulching applies organic or inorganic materials to the soil surface to reduce evaporation and suppress weeds.
  • Conservation Tillage reduces tillage to maintain crop residue on the soil surface, reducing evaporation and improving water infiltration.
  • Cover Crops involve planting crops to protect the soil surface, improve soil structure, and reduce water loss.
• Deficit Irrigation:
  • Involves applying less water than the crop's full water requirement.
  • Can improve water use efficiency in some crops without significantly reducing yield.
• Reuse of Treated Wastewater:
  • Uses treated municipal or industrial wastewater for irrigation.
  • Requires careful management to ensure water quality and prevent soil contamination.
• Lining of canals and watercourses to prevent water loss during conveyance.

Crop Water Requirements

• Crop water requirement is the total water amount a crop needs to grow and produce optimum yield.
• Factors affecting crop water requirements:
  • Climate:
    • Temperature: Higher temperatures increase evapotranspiration.
    • Humidity: Lower humidity increases evapotranspiration.
    • Wind: Higher wind speeds increase evapotranspiration.
    • Solar Radiation: Higher solar radiation increases evapotranspiration.
  • Crop Type:
    • Different crops have different water requirements based on their physiology and growth habits.
  • Growth Stage:
    • Water requirements vary throughout the growing season, with peak demand typically during flowering and fruit development.
  • Soil Type:
    • Soil texture and structure affect water infiltration, water-holding capacity, and drainage.
  • Management Practices:
    • Irrigation method, planting density, and fertilization influence crop water requirements.
• Determination of Crop Water Requirements:
  • Evapotranspiration (ET) is the primary factor.
  • ET can be estimated using weather data and crop coefficients.
  • Crop coefficients (Kc) adjust ET based on the specific crop and its growth stage.

Drainage Systems

• Drainage is the removal of excess water from the soil surface and subsurface.
• Importance of Drainage:
  • Prevents waterlogging, which reduces crop yields and damages plant roots.
  • Improves soil aeration, promoting healthy root growth and nutrient uptake.
  • Reduces soil salinity risk from salt accumulation near the surface due to poor drainage.
  • Facilitates timely field operations like planting and harvesting.
• Types of Drainage Systems:
  • Surface Drainage removes excess water from the soil surface.
    • Land Grading shapes the land surface to promote runoff.
    • Open Ditches are channels that collect and convey surface water.
  • Subsurface Drainage removes excess water from the soil profile.
    • Buried Drain Pipes are perforated pipes installed below the soil surface to collect and convey water.
    • Mole Drains are temporary channels created by pulling a mole plow through the soil.
    • Vertical Drainage uses wells to pump water from the subsurface.
• Design Considerations for Drainage Systems:
  • Soil type and hydraulic conductivity must be considered.
  • Rainfall patterns and waterlogging frequency.
  • Crop type and tolerance to waterlogging.
  • Topography and slope of the land must be factored in.
  • Outlet availability and capacity.