The recent rains were a welcome relief for many parts of our state, but we are still in a serious drought with our reservoirs and snowpack at historical low levels. Ensuring adequate water for crops will be a challenge this year.
In general, perennial crops, such as orchards and vineyards, cannot survive extended periods without irrigation. However, alfalfa is more resilient because it can go into a drought-induced dormancy over the summertime, at least for one year. The tradeoff is that without water there will be little yield, but research has shown that the stand will persist on most soil types and yield will recover the next year once water is applied to the field again.
In most years hay growers rely on winter rainfall to fill the soil profile. This has not happened yet and the growth of many alfalfa fields is behind due to the lack of moisture. Frost also impacted a number of fields this winter, especially new stands, causing delayed growth. The drought may also be exacerbating the impact of aphids in alfalfa fields in some parts of the state, further stunting fields.
Unless the recent rains continue and are sufficient to refill the soil profile, growers should apply water to alfalfa to ensure adequate soil moisture so that first cutting yields are maximized, since they tend to be of highest value. Once we fall behind on water for perennial crops, it is hard to catch up due to the high evapotranspiration rates during summertime.
When water is scarce, summer could be a time to allocate water from alfalfa to other crops that must have water. However, depending on residual soil moisture content, alfalfa yields will likely be reduced by 90% or more. No one wants to dry up a field and forgo the potential income and feed for animals. However, in a year like this, producers may not have many options and drying up an alfalfa field for part of the season might be a viable option because of alfalfa's ability to recover once the field receives water the following winter. Deficit irrigation for more than one year though may be damaging to alfalfa hay fields.
Additional information on the impact of deficit irrigation can be found on the UC ANR Alfalfa and Forages website at http://alfalfa.ucdavis.edu. Under the top heading, ‘Symposium' and ‘Search Proceedings', enter ‘Deficit Irrigation' in the query box. More resources on drought issues in California can be found on the UC ANR California Institute for Water Resources website (CIWR) at http://ciwr.ucanr.edu/.