Field Application Efficiency

Question 1

Explain uniformity, adequacy and field application efficiency and/or explain their relationship (impact of uniformity and adequacy on application efficiency using graph)

Answer 1

• Uniformity = how evenly water is applied
• Adequacy = the percentage of the field which receives at least the prescribed irrigation dose
  Field application efficiency = (water useful output)/(field input)
• High adequacy using a field application system with low uniformity leads to over‐irrigation and therefore to a very low irrigation efficiency. Good uniformity of an irrigation system is needed for a good efficiency. Lower adequacy helps increase efficiency - don’t need to irrigate to 100% so same amount of irrigation leads to higher efficiency

Question 2

Discuss the difference between pressurized systems and surface irrigation systems in terms of application uniformity (source of non-uniformity differs; metric for degree of uniformity differs). Also reflect on what this means for application efficiencies of drip, sprinkler and surface irrigation (compare without giving the exact efficiency numbers)

Answer 2

• Surface irrigation: water flows by gravity through canals to the field e.g furrows
  > To determine uniformity, need to determine how much water actually infiltrates root zone - requires sampling of root zone before and after application - often labour intensive
  > Intake point receives more water (infiltration highest near inlet) - want to supply crop water requirement to entire field - because of low uniformity, part of field needs to be over irrigated
  > Non uniformity is hard to measure
• Pressurized: pumps pressurise water in pipes to fields e.g. sprinklers, drip
  > Use catch cans to determine uniformity, easy to do
  > Use coefficient of uniformity, UC
  > Non-uniformity comes from pressure variation positioning of sprinklers, wind drift

Question 3

Compare two or more specific irrigation methods (form the list) and explain their differences in irrigation efficiency

Answer 3

• Drip or localized irrigation = only root zone around the plants is supplied with water, soil evaporation is very minimal, can decide when to irrigate, little risk of runoff generation, little wind drift loss, low energy requirements, not labour intensive, easily supply nutrients directly to the crop, root zone always supplied with water = salts cannot concentrate. Cons = large installation cost, education and training needed, requires high standards for water quality to avoid mechanical and chemical clogging, need more advanced scheduling
• Sprinkler systems = can be applied on any terrain and on most soil types (can choose precipitation intensity and make sure its kept below the infiltration capacity of soil), fertilizers can be added to sprinkler, can be automated, can be portable, higher efficiency than surface irrigation. Cons = requires energy for pumps or a pressurized water source, under low humidity and high winds the losses can be significant, drops are larger than rain so can damage soil structure and leaves
• Travelling versus fixed sprinkler systems = portable requires labor when you need to move the sprinklers but is cheaper. Fixed - most of the time parts of system are not used
• Surface systems versus pressurized system (see above)
• Furrow (and border): labour intensive, can take hours to fill furrow, can only function if grading is precise. High classical efficiency and small degree of non uniformity
• Basin (rice as special but very important case) = low dykes are constructed around the field. Cons = not suitable for steeper slopes, not suitable for all crops, requires lots of water, lots of percolation losses (don’t use sandy soil with high K), extra water needed for pre-saturation of root zone, all rainfall is effective (surface run off is prevented), 100% application efficiency

Question 4

Explain one of the hydraulic summary graphs for furrow irrigation discussed in class or in the MOOC (graph will be provided).

Answer 4

FIGURES