Why Aren’t California Farmers Converting from Flood to Drip Irrigation?

With 80% of California water use devoted to agriculture during this historic drought, you would think that farmers would be making a massive shift from flood irrigation to drip irrigation, with a corresponding shift to drip-friendly crops (away from alfalfa, cotton, rice to tomatoes, peppers, other vegetables). A closer look reveals that while drip has much higher yields and produces less ag waste, it is more expensive. That drip uses less water is controversial is some circles, since flood irrigation is thought to “recharge the aquifer”. That the “aquifer” has been abused by farmers is yet another related issue.

Flood irrigation for a sugar crop

According to a recent study by the Union of Concerned Scientists, California Central Valley farmers produce over 250 crops with a yield of $17 billion/yr, which is supplies about 25% of the Nation’s food. However, even though it contains 1% of the Nation’s farmable land, the Central Valley farmers use 17% of the Nation’s (and 70% of California’s) irrigated lands, and a staggering 20% of the Nation’s groundwater (groundwater tables have dropped over 100 ft in some areas). The result is the high impact of fertilizers, pesticides, and agricultural wastewater (largely calcium carbonates and salts that come from the mountains, capable of poisoning soils and wildlife), but more imminently a shortage of water. In previous drought years, some ag lands were simply not farmed (leading to job and production loss) while some thirsty high-value crops (like almonds and pistachios) survived due to their higher profit-margins. The Sustainable Groundwater Management Act (SMTA), passed in 2014, is more conceptual but a step towards necessary groundwater regulation. Healthy Soils Programs (HSPs) are also conceptual, and related to better water management. It is estimated that a complicating factor will be increasing temperatures, which may prohibit the growth of some fruit and vegetable crops by 2060 (unless offset by energy intensive solutions). Despite recent droughts and innovations, 40% of California farmers still use flood irrigation, about 2% spray irrigation, and the rest drip. Against this backdrop, we will now discuss conversion from flood to drip irrigation, which offers a better usage of water at a somewhat higher energy cost. (DeLonge,2022),(Charles,2021),(Weiser,2016)

Water Rights-A History: I should begin with a brief history of who has water rights in the Central Valley, and how they work. Most of this was set up by Roosevelt in the Central Valley Project, in 1933. Major dams collecting water from the Sierras (and elsewhere) are Folsom, Friant, New Melones, San Justo, San Luis, Shasta, Sly Park, Trinity, and Whiskeytown (all in the Northern half of the State). The Central Valley Project was supplemented in the 60s by the State Water Project, providing additional farm and municipal deliveries. At this point, know that about 80% of California water delivery goes to ag, while 20% goes to municipalities. Currently, about 48% of all runoff is set aside for environmental use (not diverted so as to benefit fish and other animals/plants, which is controversial). Historically, if you farm within a water district, you have access to surface water delivery, at a price of about $70 per acre-foot (to compare, Los Angeles pays about $1000 per acre-foot for water). If you don’t belong to a water district, you pump the aquifer, but those days are coming to an end (while some farmers will need to let their land go fallow, some small towns will implement drastic reductions in deliveries). For the record, the other large water districts in the State are Hetch Hetchy (SF Bay Area), the Colorado River System (serving the Imperial Valley and others through Lake Mead), the Los Angeles Aqueduct (delivering water from the Owens Valley), and the Mokelumne Aqueduct (serving Oakland and other East Bay cities). Farmer’s water rights in the West have tended towards a kind of “use it or lose it” policy, but new policies allowing them to sell excess water is encouraging water conservation. (Charles,2021),(Lustgarten,2015)

California water distribution, in wet and dry years

The Benefits of Drip Irrigation: The benefits of drip irrigation would appear to far outweigh the disadvantages. Though the statistics vary by crop, a recent study involving guayule rubber plant production (a crop grown in the Southwest to produce rubber), shows that at a cost of 13% more energy, yields were 49% higher while environmental impacts were 51% lower. The report goes into great detail, but generally speaking the following accounts for these overall numbers:

1) Drip uses more energy due to pumping costs

2) Drip produces about 50% higher crop yield due to more efficient water distribution and fewer weeds.

3) Though drip has higher environmental impacts due to increased energy (pumps), plastic (distribution) and sulfuric acid use (distribution cleaning), it has less overall impact due to lower water and fertilizer usage, less need for herbicides/pesticides, and lower ag wastewater byproduct.

Note here that the report does not specifically put a number on “how much less water does drip use versus flood for guayule rubber?” As we shall see, this number is somewhat hard to calculate and is somewhat politicized. Note also that prior to this study, most all guayule rubber was grown using flood irrigation, as though the farmers didn’t even think drip was possible, even though it proved to be more efficient (all things considered). The latter concept is also somewhat tied to politics. (Eranki,El-Shikha,Hunsaker,Bronson,Landis,2017)

The Benefits of Flood Irrigation: If you ask any Central Valley farmer or ag consultant, they will say “flood irrigation recharges the aquifer”, sort of ignoring all the related evaporation, soil contamination, inefficiency, and herbicide use. However, in fairness, flood irrigation does have some advantages. For starters, it is cheap to set up and run, given the generous Central Valley water rights given out many years ago, along with the many dams and canals guiding Sierra runoff to relatively flat and fertile land (“flat” is important, as laser-levelling has made flood irrigation more efficient) . It generally runs with gravity and siphons, and without pumps. Some crops have traditionally been grown with flood or spray irrigation (spray irrigation is another subject beyond this article), since the plant roots are too numerous for drip emitters (examples: alfalfa, corn, wheat) although this is changing. Nut crops such as almonds have also traditionally used flood irrigation, although some are starting to use drip. The typical pros/cons of almond drip systems are cited, high yield/less water/fewer weeds but with higher energy/maintenance costs. Generally speaking, the “benefits” of flood irrigation are skewed towards expediency-loving farmers who have generous water rights and are able to pump the aquifer dry, while drip offers somewhat higher cost, with much great societal benefit (less water, chemicals, soil contamination) (Chen,Xiong,Chang,2021),(Johnson,2017)

Drip irrigation, applied to a tomato crop in Tunisia

Flood Advocates Ignore the Long-term Impacts of Soil Depletion: Soil depletion is probably the biggest argument against flood irrigation (beyond inefficient delivery due to evaporation and unwanted runoff). In addition to the buildup of increased chemicals in the soil (herbicides and the like, whose impacts are not entirely known), the larger amounts of flood irrigation brings salts from the mountains that build up in the soil, creating a hardpan crust. This salt buildup gradually poisons the soil while the hardpan prevents percolation into the aquifer (and proper root penetration). The State recognized this problem and set about making an agricultural wastewater system, meant to drain excess ag water into a canal that would deliver this water back to the San Francisco Bay. Funding for the project ran out, and the ag wastewater settled into a pond at the Kesterson Marsh (near Gustine, CA). In the early 80s, birds attracted to Kesterson began dying and hatching deformed offspring, later related to dangerous levels of Selenium (a salt coming from ag water delivered from the Sierras). There are many other related soil depletion issues (many involving the problems of tillage and poor ground cover, tangential to this article), but needless to say, drip irrigation is erring on the side of environmental caution. (Horne,2009)

Complicating Factors: The general direction of ag water use reminds one of oil extraction, a sort of “if we’re going to continue to do this, we need to charge more money, work more cleanly and discretely before the resource disappears”. Complicating factors would include the aforementioned a) depletion of the aquifer b) gradual poisoning of the soil using flood irrigation c) further poisoning of the environment, mostly with flood related herbicides and sometimes eutrophication of receiving waters (ie excess algae growth from overfertilization) d) increasing temperatures and e) increasing energy costs, if not f) the depletion of surface water in the West. Generally speaking, drip solves a-c, but not completely d-f (though it may help in the right scenarios). As a society, we should be prepared to spend more for our food, to offset water, energy, and environmental impacts using drip. It would be a great help if cleaner (and cheaper) energy sources would emerge, plus better plastic recycling technologies. As for higher temperatures, this is definitely bad for flood (more evaporation, which is already a big problem), but not necessarily a problem for drip (crops can be grown under controlled conditions, but again with higher energy costs).

What is Happening: Through the California Sustainable Groundwater Protection Act (SGPA) and Healthy Soils Program (HSP), the Central Valley and State are taking steps in the right direction. However, Central Valley Farmers are continuing to flood irrigate and pump the aquifer dry. These farmers tend to be conservative, hate regulation (sometimes for good reason), and tend to believe their water rights are sacred. They also believe they are feeding the Nation, and have the rest of us by the “nuts” (with some merit). Governor Brown had the mediative power to resolve some of this, but I suppose it will take a few more drought years (and increased vegan demand) to convince flood irrigators to convert away from flooding cotton, rice, and alfalfa crops to drip irrigating tomatoes, onions, and peppers. In fairness, many farmers are beginning to drip irrigate the former three, but they will always be thirsty crops best grown elsewhere.

Kesterson Reservoir was welcoming to birds, but also deadly due to selenium in ag wastewater

What Needs to Happen: There needs to be an increase in groundwater regulation, probably involving metering and allotments (otherwise, one farmer can deplete everyone else’s groundwater, not necessarily for efficient crop growing). There probably needs to be a “water tax” for high-value (and thirsty) crops (like almonds and pistachios) which encourages drip use. There also needs to be incentives for farmers to pay the additional costs associated with drip (in the form of water discounts, grants, or subsidies). Marc Reisner, the author of the famous “Cadillac Desert” book, once proposed that CA municipalities gain ag water rights in exchange for drip investment, but I suppose these water rights are too valuable for that now. More studies need to be done to offset the myth that “flood irrigation recharges the aquifer” as a) Much flood water evaporates before it gets to the aquifer b) when it gets there it brings dangerous salts and c) If the farmers can’t be trusted to pump the aquifer properly then flood irrigation is a license to waste. Rodents (mostly gophers) are also a problem in drip irrigation (they love to chew up plastic water lines), and better rodent management methods are needed.

Conclusions: So how much water does drip save over flood irrigation? The best number I could find was about 70–80%, in the study cited below. The Weiser study stating that over 50% of farmers ARE using drip is encouraging. Water in the West has always been contentious. Many myths have been made about water delivery, as a pretext to fortunes made in real estate and agriculture. Central Valley farmers have mostly flood irrigated all these years, since they had water rights, political power, and it was easy. They have created a somewhat false justification that “flood irrigation recharges the aquifer”, when in fact that has several caveats. Water rights were handed out rather unfairly around 100 years ago, while all of us have been using groundwater disproportionally and with no regard to future generations. Yet despite all of this, drip irrigation offers many solutions, if the consumer is willing to make some dietary changes and inducements are made to farmers for drip conversion. (Tagar, Chandio, Mari, Wagan, 2012)

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Vern Scott

Scott lives in the SF Bay Area and writes confidently about Engineering, History, Politics, and Health