Root and top growth were measured immediately after drainage and again three weeks after drainage. This three-week wait and cut period would be similar to irrigating three weeks before harvesting the alfalfa. Yields of alfalfa can be significantly reduced by wet or flooded soil. High water tables accompanying spring thaws and exceptionally heavy rains can inhibit alfalfa growth. Wet soil can reduce stand vigor and promote fungal root infection.
Periodic inundation can create short-term flooded conditions that 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. Irrigators should avoid prolonged flooding of irrigated alfalfa when irrigation water temperature is high. There are two reasons for this. First, colder water will hold more dissolved oxygen and the cool air temperatures will keep the alfalfa demand for oxygen relatively low.