Survey

2.Testing the Irrigation Water Source

 

Before implementing routine or remedial maintenance on a micro-irrigation system, test the water source for physical, chemical, and biological properties to determine emitter plugging potential. It is important to take a representative water sample:

  • If the water source is a well, collect the sample after the pump has run for about half an hour.
  • If sampling surface water, collect the sample near the center of the source about 1 ft below the water surface.
  • Check for water source variability by taking samples several times during the irrigation season.
  • To accurately measure water pH, alkalinity, dissolved iron, and hydrogen sulfide, analyze well water with a field test kit immediately after sampling.
  • Use Table 1 to estimate the plugging hazard of irrigation water based on a standard analysis.
 
Table 1. Chemical criteria for plugging potential of micro-irrigation water sources (Pitts, 1990).
Factor Plugging hazard based on concentration
  Slight Moderate Severe
pH <7.0 7.0 to 7.5 >7.5
Total dissolved solids 1 < 500 500 to 2000 >100
Suspended solids 1 <50 50 to 100 > 2000
Iron 1 < 0.1 0.1 to 1.5 > 1.5
Manganese 1 < 0.1 0.1 to 1.5 > 1.5
Calcium 1 < 40 40 to 80 > 80
Hardiness as CaCO31 < 40 40 to 80 > 80
Hydrogen sulfide 1 < 0.2 0.2 to 2.0 > 2.0
Bacteria (#/mL) < 10,000 10,000 to 50,000 > 50,000