Irrigation

• Irrigation


  The artificial operation supplying the need of a plant for water, necessary in dry climates where natural rainfall does not meet plant water requirements
• Irrigation is a prerequisite for agriculture
• Irrigation


  • Major part of water loss is to the atmosphere through evapotranspiration, infiltration, percolation, seepage, runoff
  • Assured and timely supply of irrigation water has a great influence on the yield of the crop
• Factors influencing crop water requirements

  • Irrigation needs are determined by climatic factors, not just drought or visible crop failure
  • Amount of water used by a growing crop is governed almost entirely by prevailing weather conditions
  • Soil moisture is depleted through evapotranspiration and drainage
• Rice growth in Asian countries

  • Expansion of irrigated land accounted for more than half the output increases in many countries
• Lack of water control was identified as accounting for up to 40% of the difference between the apparent potential and actual national yields in the Philippines
• Poor irrigation


  • Inadequate water being supplied to the rice crops
  • Supply of excess water
• Continuous Submersion Method (rice irrigation)

  1. Water kept at 10cm for 1 week after transplanting

  2. Shallow submergence during tillering period

  3. Drainage and drying of top soil during tillering

  4. Continuous flow irrigation or drainage and renewal of water once/twice

  5. Gradual drainage during ripening period to facilitate harvest
• Intermittent Irrigation Method (rice)

  1. Soil water content kept slightly below saturation, then water added until shallow submergence

  2. Saves water by reducing surface runoff and percolation losses, increases effective rainfall use
• Head Stage Submergence Method (rice)

  Soil kept saturated/lightly submerged except 25 days prior to 10 days after heading, when 10cm submergence
• Water Saving Irrigation Method (rice)

  Soil water content kept at min 75% of full saturation, moderate submergence only 30 days from head initiation to end of flowering
• Methods of irrigation


  • Surface irrigation
  • Sub-surface irrigation
  • Overhead (sprinkler) irrigation
• Continuous Flow (surface irrigation)

  1. Same discharge flows continuously day and night, based on land area

  2. Simple for canal operators but inefficient, can lead to water wastage

  
• Rotational Flow (surface irrigation)

  1. Water supplied continuously but irrigators take turns using it for a fixed time on a fixed day

  2. Allows for time to fill and empty farm channels

  3. Requires good cooperation between irrigators and canal operators
• On Demand (surface irrigation)

  1. Irrigators can take water from the system at any time

  2. Efficient but expensive to construct, requires cooperation to prevent overloading
• Reservoir (surface irrigation)


  1. Reservoirs/canals filled continuously, irrigators take stored water when convenient

  2. Combines ease of continuous flow with convenience of on-demand

  
• Sub-surface irrigation


  Water applied only to the root zone via underground perforated/porous pipe network

  
• Overhead (sprinkler) irrigation


  • Water applied to land in the form of a spray, resembling light rainfall
  • Useful where surface irrigation methods are not efficient
• Effects of poor irrigation

  Reduced crop yield

  Lodging - permanent displacement of plant stems from the vertical position as a result of irrigation weakening the soil.
• Irrigation scheduling practices


  Continuous submersion method, Intermittent Irrigation method, Head Stage Submergence method and Water Saving Irrigation Method
• Methods of Surface Irrigation

  Continuous flow

  Rotational flow

  On-demand

  Reservoir
• Timeshare


  Water sharing in rotational flow