UC Davis irrigation experiment shows big increase in alfalfa yield per acre foot of water

Cleverly managed deficit irrigation (when you significantly reduce water applied during the hot part of the year) substantially increased yield per unit water applied in a new study by researchers at UC Davis. In controlled side-by-side field experiments, Dan Putnam and his colleagues demonstrated that if you do it right, a big reduction in water applied will result in just a small reduction in yield.

The technique involves full irrigation for a good part of the year, but an irrigation cutoff in the hottest part of the summer. That’s the time of year when alfalfa can drink up a lot of water for not much additional yield. This reflects something farmers have long known – that alfalfa is a sturdy crop, offering resilience in a drought. When summer supplies run low, the plants hunker down. Yield drops, but they don’t die.

I talked about this in my book:

This opens up interesting policy options. If, say, the water saved was sufficiently valuable to a municipal water user to compensate the farmer for the lost yield in return for sending the saved water off to the city, you’d have the room for a deal that keeps the land in production and the farmer in business while also providing water to the city.

This sidesteps the biggest criticism of agriculture-to-urban water transfers—that they dry up land and community livelihoods. “Buy-and-dry” has become an epithet in the Colorado River Basin, and deficit irrigation provides an alternative if we can get the institutional arrangements right. By one calculation, widespread use of intentional deficit irrigation in alfalfa fields in Arizona and Colorado irrigated with Colorado River water could save nearly four times as much water per year as the annual consumption of the Las Vegas metro area.

The citation for that last bit leads to Michael Cohen and colleagues’ 2013 analysis of Colorado River Basin agriculture.