Types of irrigation:

• canal and drainage systems - flood fields with water
• center pivot irrigation, spray vs. drip.
• drip irrigation - direct supply by hoses.
• UNL site on types of irrigation.

Soil salinization:

• cycles of irrigation and some numbers to play with.
  • salinity of seawater: circa 35,000 ppm
  • salinity of input irrigation waters 350 ppm.
  • >2000 to 3000 ppm toxicity level for many crops
  • critical question: if the climate is arid enough that water evaporates out of soil where does the salt go?
• extent of concern?
  • San Joaquin valley in California, Pakistan, "half of the world's irrigated land .... suffers from reduction of crop yields due to salinization."
• possible solutions:
  • desalinize irrigation water (very expensive).
  • direct trickle irrigation (water usage reduction).
  • tile fields: can flush salts through soil, but run off waters high in Selenium in California, and expensive.
  • salt resistant crops via genetic engineering (potentially only delay problem).

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