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Why Alfalfa is the Best Crop to Have in a Drought
By Daniel H. Putnam, Alfalfa & Forage Specialist, UC Davis and Member of the California Alfalfa & Forage Association Board of Directors

The 2013-2015 drought has brought much public attention to the amount of water used in agriculture, and particularly which crops use the most water.

Although almonds have taken the hit lately, alfalfa is often one of the favorite whipping boys of agriculture critics due to its high water use on a statewide basis. 

But is alfalfa's water profile really so miserable?

Contrary to popular belief, alfalfa has several unique positive biological properties and advantages when it comes to water.  Due to these properties, alfalfa is remarkably resilient when it comes to severe drought conditions.

First a clarification -- Alfalfa does not really use more water than other crops.  At full canopy (when the leaves cover the soil surface), alfalfa's water use is not much different than any other crop (think spinach, lettuce, tomato, wheat, almonds or corn) per unit time.  The Evapotransporation (ET) requirement (the amount of water a crop really needs to grow) is remarkably similar across crops at full canopy.

Alfalfa's water use in California is primarily due to its high acreage and nearly year-round growth pattern in many regions.  If spinach were continually grown on 850,000 to 1 million acres all year long, the water use would be about the same as alfalfa, perhaps more.

Further, it's not so much how much water is used, but how much crop is produced per unit of water that is important -- also known as water-use efficiency.  In that category, alfalfa shines.

Contrary to popular belief, alfalfa has several unique valuable properties and advantages which would enable cropping systems greater resiliency under drought conditions.

UTILIZING BIOLOGICAL FEATURES OF ALFALFA IN A DROUGHT

Alfalfa has a range of biological characteristics that make it very useful when a farm or an irrigated region is faced with drought conditions and resulting water limitations.  These are:

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.

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).

Salt Tolerance/Ability to Utilize Degraded Water - Recent data has shown that alfalfa has a high degree of salt tolerance.  A recent trial in Fresno County, where EC 5.5 water was used for irrigation over 3 years, yields were normal (10-12 tons/acre).  This is important in a drought, since degraded recycled water (municipal waste water, drain water, other waste water) could be used on this crop, while saline waters would injure less-tolerant crops.

Contribution to Wildlife Habitat - In a drought, all of nature suffers.  Alfalfa has been shown to be a significant wildlife habitat due to its lush foliage and insect diversity.  Biologists have determined that 28% of California's wildlife use alfalfa for nesting, feeding or cover.  Even partial-season irrigation during drought can assist wildlife in surviving a drought period by using alfalfa as habitat.  Don't believe it?  Visit an alfalfa field and observe the egrets, curlew, hawks, eagles, snakes, deer, antelope, elk, insects, and many other birds and mammals who are at home there.

Ability to Survive a Drought - Alfalfa evolved in regions of the world with long hot dry summers and wet winters - exactly like California.  Although yields are highest with full irrigation, alfalfa can survive periodic droughts.  This is due both to deep roots as well as the ability to go "summer dormant" under dry conditions.  In 2014, Central Valley growers that were forced to stop watering their alfalfa field generally found the crop recovered after rainfall or irrigation resumed later in the year.

Ability to Deficit Irrigate: Obtain Partial Yields - Typically 50-60% of full yields are obtained by mid to late June.  If only partial water is available, irrigation water can be applied early (supplemented by winter rains and residual moisture), and the crop dried down during late summer periods.  This is particularly important, since water is scarcer in late summer vs. early, and that water may be used for other crops or uses, or economically transferred to cities.  Additionally, Water Use Efficiencies are greatest early in the year, and yield and quality tend to be higher early vs. late.

FLEXIBILITY IS THE KEY

It is the combination of deep roots, ability to utilize rainfall early in the year, high water use efficiency, abiltiy to survive droughts, salinity tolerance, and ability to give partial yields with as much as half of the irrigation water that makes alfalfa particularly valuable in a drought.

University of California work done over the past 20 years has confirmed the ability for growers to stop alfalfa irrigation in mid-summer, allow the crop to dry down, and re-water successfully later when irrigation water becomes available.  One cannot do this with many other crops.

Summer-grown annual crops (corn, cotton, tomato, sunflower) also have a high degree of flexibility --  in the sense that one could elect not to grow those crops during a drought, thereby reducing water used for these crops to zero.  But yields are also reduced to zero.

High value vegetable growers are unlikely to sacrifice any water since the economic value of those crops is so important to their farms.  Additionally, one cannot really deficit irrigate spinach, broccoli, onions, lettuce, or strawberries too much and expect an economic product.

Winter grown annuals (wheat, oilseeds) and safflower also have major advantages during drought, since they can be grown with very little irrigation water, and can be eliminated during low water years.

Orchards have the least flexibility in a drought, due both to significant yield reductions when less-than-full irrigations are applied, but also the significant economic risk to the farm because of the high investment cost.

SUMMARY

Contrary to some popular views, alfalfa has a range of positive biological characteristics that should be quite useful when facing water-short conditions.  These characteristics include a high degree of flexibility to "deficit irrigate" the crop, ability to survive drought periods, high water-use efficiency, deep rootedness, salinity tolerance, and the ability to utilize degraded water.  It is additionally very valuable to wildlife, which also suffers during a drought.

Oh, and by the way, it is also very valuable to millions of consumers who depend upon the milk, cheese, yogurt, and yes, ice cream, produced from alfalfa. 

 


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