[codenesium]

It probably makes a huge difference how the irrigation is applied. Flooding land with water or digging trenches and running water to crops is a lot less efficient than drip emitters on each plant. Obviously doesn't work for stuff like alfalfa but they shouldn't be growing that anyway...

[kolanos]

Alfalfa is one of the most water efficient and nutritionally rich crops there is. It is also one of the most drought resistant crops. It is hearty and reliable, unlike corn which is far more wasteful when it comes to water.

> Deep-Rootedness—alfalfa roots are commonly 3-5 feet deep and can extend to 8-15 feet in some soils. Therefore this crop can utilize moisture residing deep in the profile when surface waters become scarce. It shares this property with crops such as orchards, vineyards, and sugarbeets and safflower, unlike crops such as onion, lettuce and corn, where it's easy to lose water past the root zone.

> Alfalfa's deep roots are capable of extracting water from deep in the soil, thus much of the water applied is not wasted. Additionally, deep roots enable the crop to survive periodic droughts.

> Perenniality—The fact that the crop grows for 4-8 years, grows quickly with warm conditions in the spring is a major advantage of alfalfa—it can utilize residual winter rainfall before irrigation is necessary. This is unlike summer-grown annual crops that need to be replanted each year (water use efficacy is low during this time). In many areas, the first cutting of alfalfa of the year requires zero irrigation– supported only by rain and residual soil moisture.

> Very High Yields—Alfalfa is a very high yielding crop, and can grow 365 days a year in warm regions (such as the Imperial Valley of California and southern Arizona). Its biomass yields are very high—we can get up to 12 cuttings per year in those regions, and growers with top management can obtain more than 14 tons/acre dry matter yields. High-yields create higher water use efficiencies.

> High Harvest Index, High Water Use Efficiency—Alfalfa's Water Use Efficiency is not only due to high yields, but because nearly 100% of the above-ground plant material is harvested (known as the harvest index). In most seed-producing and fruiting crops, only a portion of the plant is harvested (typically 30-50% of the total plant biomass).

[0]: https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=1772...

[jeffbee]

Flooding rice fields in Glenn County is essentially 100% efficient because all of the water returns to the Sacramento River or recharges aquifers. Watering orchards in west Fresno County returns all of the water to the atmosphere via transpiration. Even though superficially a rice field looks wasteful, they are on two opposite extremes.

[SamBam]

Doesn't a large percentage of the water flooding a rice field in Glenn County still evaporate, both before it enters the plants/aquifer, and later through transpiration?

I don't know the percentages (but would love to learn) but it's certainly not zero.

[jeffbee]

Sure, but the denominator for flooded irrigation is huge, so the efficiency is high. That's why flooding is a superficial and not substantial problem. The plant transpires water at a certain rate and a certain density per ground area. That rate isn't influenced by whether the field is flooded or drip-irrigated. By the way flooding also provides wildlife habitat.

Anyway I'm just tired of the meme about growing rice in a desert. California rice country isn't a desert, it exists in places that were annually flooded before flood control engineering, and should still get flooded for various reasons. It is not a waste of water.

[prostoalex]

Returning to the atmosphere is not really sustainable, is it? Sure, it enables a rainfall at some point, but not necessarily at the time and the place you need it next year.

[jeffbee]

No, it is not sustainable at all. They are pumping out fossil water in California and whatever portion of it falls as rain does so hundreds or thousands of miles to the east.

[codenesium]

How does returning it to the river solve the problem of their isn't enough groundwater? That water goes back into the ocean where it's stuck if it never rains.

[jeffbee]

Yeah but that's not really what happens to Sacramento River water. It's all diverted downstream for other uses. The Tracy pumps that raise the water from the delta into the aqueduct are the largest energy consumer in the state.