State Farmers May Fall Back on Sewage to Irrigate Crops

California farmers, facing increasing demands from other interests for the water they use to irrigate crops, might be able to get a little help from city sewage effluent.

It’s not an attractive-sounding idea, but it isn’t altogether unusual, say some officials who analyzed the subject.

Application of municipal waste water on land is common in many arid and semiarid regions of the world, said Takashi Asano, water reclamation specialist with the state Water Resources Control Board, and G. Stuart Pettygrove, a University of California, Davis, Cooperative Extension soils specialist.

‘Logical and Important’

“In some regions, 70% to 85% of such water is used for agricultural and landscape irrigation,” they report in California Agriculture, a magazine devoted to UC farm-related research.

“As demand for water increases in this country, irrigation with reclaimed municipal waste water has become a logical and important component of total water resource planning and development,” they add.

In California, the push for more water was underlined at state Water Resources Control Board hearings earlier this year on the beneficial uses of irrigation water imported through the Sacramento-San Joaquin Delta. One farmer said the San Joaquin Valley needs an extra 1 million acre-feet of irrigation supply, and a just-released state study estimates the need at 800,000 acre-feet in the Central Valley.

However, some speakers contended that less water should to be sent south to farms and Southern California so the quality of the delta and San Francisco Bay can be preserved better.

Asano and Pettygrove suggest that treated municipal waste water could provide part of the solution. In fact, they say about 220,000 acre-feet of municipal waste water from 240 California communities is already used for agricultural and landscaping irrigation.

Another 610,000 acre-feet of treated waste water “is incidentally reused after it is discharged and enters surface or ground waters,” they add.

Of the treated sewage that is intentionally reclaimed, 57% is used on fodder, fiber and seed crops, 14% goes on golf courses and other landscaping and 7% is used on orchards, vineyards and other food crops, they say.

Waste water can contain too much salt for healthy crops or even too much of the nutrients plants need to grow, such as nitrogen and phosphorus, the article notes.

But it adds that a study of waste water used on crops in Fresno and Bakersfield indicated that such problems were minor.

That study by K. Tanji and R. S. Ayers found no salinity problem from the Fresno or Bakersfield applications and no toxicity problems with chloride used to treat the water or with boron or heavy metals.

In sensitive crops, slight to moderate problems were found with salt toxicity using sprinkler irrigation. The Bakersfield waste water didn’t cause any problem if surface irrigation was used, but a slight problem showed up with that method in the Fresno applications, the study added.

Nitrogen, Phosphorus

Slight to moderate problems were found with excess nitrogen and bicarbonates on susceptible crops.

The Fresno sewage treatment plant provides effluent for a 600-acre farm where cotton, corn, alfalfa, almonds, wine grapes, seed beans, winter cereals and sorghum are grown.

The Bakersfield treatment plant provides effluent that is used on 5,100 acres of crops, including cotton, corn, alfalfa, sorghum, rice and irrigated pasture. Low-nitrogen water is blended with the effluent to help nitrogen-sensitive crops such as cotton.

‘No Serious . . . Problems’

The Ayers and Tanji study found “that good normal farming practices used in the area should allow full production of adapted crops,” said the report by Asano and Pettygrove.

Research indicates that “there will be no serious potential agronomic or public health problems in the use of reclaimed municipal waste water from those cities,” they concluded. “In fact, both projects have been operated for many years with few problems stemming from poor water quality.”

Treated municipal waste water also has been used to irrigate test plots near Castroville in the Salinas Valley. A five-year study found no significant public health risks and no soil or ground water degradation from irrigating that land, which was used to grow vegetables eaten raw.