Plant Nutrient Content of Irrigation Water

Flood irrigation of wheat

Irrigation water can be an excellent source of plant nutrients.  Some wells can be relatively high in nitrate, and 4 ft of irrigation water containing 5 ppm nitrate-N provides 54 lb N/acre.  Colorado River water contains appreciable sulfate and chloride.  Depending on the crop and amount of water applied, Colorado River water can supply roughly 20-60 times the uptake of sulfur and about 700 to 1700 the need for chlorine (Table 1).  Sulfur is commonly applied to certain crops in the Pacific Northwest and chlorine deficiency is known to occur in Oregon and the Dakotas.  Deficiencies of sulfur and chlorine are not known to occur in Arizona because of the large quantities of these nutrients applied in irrigation water. 

 

Table 1.  Crop uptake of sulfur and requirement for chlorine and amount of these nutrients applied in Colorado River water assuming for demonstration purposes certain water application amounts and yields for alfalfa, corn silage, and wheat.  Crops sufficiently supplied with chlorine may contain 70-100 ppm chlorine, but may contain up to 20,000 ppm chlorine without showing toxicity symptoms (Schulte, 2004).

 

 

Crop

Water applied

 

Yield1

Sulfur uptake2

Sulfur applied in water3

Chlorine required4

Chlorine applied in water3

 

ft

t/a

lb/a

lb/a

lb/a

lb/a

 

 

 

 

 

 

 

Alfalfa

6

8

43

2315

1.4

1653

Corn silage

4

35

20

1543

2.3

671

Wheat

3

3

38

1157

1.2

890

 

1 The yields are expressed on an “as is” moisture basis and assumed to be 12% for alfalfa, 67% for corn silage, and 8% for wheat.  The wheat is assumed to have a harvest index of 45%, and the nutrient uptake includes grain and straw.

2 Sulfur uptake calculated from IPNI, 2015.

3 Sulfur and chlorine applied in water calculated from water applied and the average sulfate-sulfur (101 ppm) and chloride (142 ppm) content of Colorado River water in 2014 from a sampling point near Yuma, AZ north of the international border and above the Morelos Dam (USGS, 2015)

4 Calculated assuming 100 ppm chlorine in the plant is sufficient for growth.  Crops sufficiently supplied with chlorine may contain 70-100 ppm, but may contain up to 20,000 ppm chlorine without showing toxicity symptoms (Schulte, 2004).

 

 

References

 

IPNI.  2015.  Nutrient Removal Calculator.  https://www.ipni.net/app/calculator/home

Schulte, E.E.  2004.  Soil and Applied Chlorine.  Understanding Plant Nutrient Series A3556. University of Wisconsin, Madison.

USGS, 2015.  NASQAN National Stream Quality Accounting Network - Data Portal.  http://cida.usgs.gov/nasqan_query/.