That means that a soil profile of fine sandy loam, four feet deep, might supply enough water for 3 weeks. Knowing that, many irrigators have already started irrigating, with anticipation of getting a little more growth before the first harvest. With that in mind, a little additional knowledge about the effect of standing water on alfalfa growth and production might be valuable. Yields of alfalfa can be significantly reduced by wet or flooded soil conditions when the air temperatures are warm and the alfalfa is vigorously growing. Wet soil conditions can reduce stand vigor and promote fungal root infection.
Periodic inundation can create short-term flooded conditions which inhibit growth.
These reduced yields are the result of direct interference with normal plant physiological processes. Soil temperature appears to be more critical than air temperature, when irrigating during mid-summer. Alfalfa was flooded and then allowed to recover before yields were measured. Alfalfa yields after 3 weeks of recovery from flooding showed that while top growth may have been normal for some time during the flooding treatment, the plants were nevertheless being damaged by the flooding from the beginning. All flooded plants at all temperatures showed yield loss compared to non-flooded plants at 3 weeks after drainage.