Irrigation

Irrigation

1. improve crop quality

2. aid harvesting in dry soils

3. reduce capping

4. aid germination

5. maintain/increase yields

6. crop requirement varies

   • climate
   • crop
     • potatoes
       • june/july
         • transpire 25-35mm/ha/week
           • equivalent to 250,000- 350,000litres/ha/week
       • apply 5mm at SMD=10mm to avoid common scab
         • BPC, 1999
       • 400mm per season
         • upto 200mm from irrigation (Shrops)
   • cultivar
   • length of growing season
   • soil type
   • soil structure
   • daily weather

7. soil water reserves deplete

   • gravitational
   • evapotranspiration
     • evaporation
     • transpiration

8. increase nutrient availability

9. low soil moisture

   • stomata close
   • transpiration falls
   • CO2 uptake reduced
   • DM reduces
   • wilt and die

10. water uptake factors

    • air temp
    • relative humidity
      • high reduces transpiration
        • low increases
    • wind speed
      • low=low
        • high=high
    • solar radiation
    • size/ development/ age
    • soil
      • water status
      • structure

11. MAFF, 1988

    • approx. 17% AWC for all topsoils and subsoils
      • silt loam = 23% & 22%
      • sands = 12% & 7%
      • peats = 35% & 35%

12. Withers and Vipond 1974

    • infiltration rate decreases over time
      • reaches terminal rate
        • 55mm/hr sand 30mm/hr loam 5mm/hr clay

13. OM increases pore volume and size

    • thus increasing infiltration and water capacity

14. ADAS Irrigation best practice guide 2003