As water costs keep going up, growers are learning to adapt by becoming much more efficient with water use, and working with ag scientists to come up with innovative irrigation methods, including reusing water.
Reusing drainage water is not new. However, it’s gained prominence in recent years given the prolonged droughts experienced by the Western U.S., and rising water rates.
Irrigation specialists with the University of California Department of Agriculture and Natural Resources (UCANR) have tried the decades-old method of cyclical irrigation, alternating good quality water with recycled drainage water.
They experimented with cotton, which they found tolerates salinity more, and tomatoes, which also showed tolerance, but with a caveat — the good water had to be used first to establish the crop before switching to drainage water.
Stephen Grattan, a UCANR plant water relations specialist found they could keep production high while increasing the quality of the fruit by increasing the soluble solids content — or brix. His team worked on it for 8 years, in order to observe the effects of salinity through several crop cycles and crop rotations, when they switched from two years of cotton to one year of tomatoes.
The study results showed that as long as the salinity level was low to start with, they could get by with irrigating with much saltier water than guidelines advised. By switching back to good quality water, the soil profile could also be reversed back to where it was, for a new vegetable crop.
A more recent trial was with the sequential method of reusing saline water, going down the food chain from salt tolerant forages to halophytes, which are plants like pickle weed that accumulate salts so they can tolerate high saline levels in the water.
Plant scientist Sharon Benes at California State University-Fresno was the lead investigator and Grattan a collaborator, and it was conducted in greenhouses and on the field, studying Jose tall wheat grass and creeping wild rye.
When salt tolerant forages were irrigated with drainage water, the water was repeatedly recycled for lesser plants. The salinity increased while the area decreased, as the water kept reducing and became concentrated as it went down the line before being evaporated through the solar evaporator.
Why irrigate weeds? “To reduce drainage volume, so it’s cheaper to dispose of or treat. With the sequence method, you get every bit of drainage water out and concentrate it, so all that’s left is a super salty remainder that gets evaporated and then you collect the dry salt,” explained Grattan.
Growers in the San Joaquin Valley in Central California have experimented with the sequential method and found that it works well for forage crops.
A third method is to blend the two types of water, which Grattan said will work if the drainage water is not too salty and is only marginally poor, as in the Imperial Valley in California’s low desert region.
Blended water can work with field crops like alfalfa, Sudan grass and wheat grass, although alfalfa is more sensitive than the others. One other suggestion he had was to establish crops like Sudan grass or wheat grass with good water, then switch completely over to drainage water, given its salinity tolerance profile.
While the cyclical or blended methods are more popular and practical compared to the sequential method, he stressed that it’s important to stay within the limits of salinity tolerance levels.