There have been many stressors on alfalfa fields this year, from early weevils to drought and hail and now fall armyworms and cutworms. Can fall irrigation help with stand stress?

For irrigated alfalfa, targeted fall irrigation may help the long-term strength of the stand. Although alfalfa is drought tolerant with its deep roots, it uses a lot of water. With warmer than normal projections for the fall, alfalfa will continue to grow and use water, depleting the soil profile.

Additionally, some moisture on the surface is necessary to prevent the roots from drying out and dying over the winter. With a full soil moisture profile headed into winter, soil temperature is better regulated, helping keep plants alive during the winter and initiating growth better in the spring.

Late season irrigation occurs during a time when evaporation is very low. This means little of what we supply will be lost, with most going to late season growth or filling the soil profile for strong spring growth. In many alfalfa fields, the water supplied during the growing season may never reach beyond 4 feet, when the roots go down 8 feet. By padding the profile now, extra water will help plants better deal with stress during high heat and high water demands next summer.

Alfalfa fields that have soils with low infiltration rates may not be able to absorb enough water during peak use periods of the year, even when supplemented with irrigation. Having a full profile going into next year for these fields to start out ahead instead of playing catch-up is one more reason for fall irrigation if available.

Watering dry alfalfa fields in the fall will help recharge water in the soil profile, combat winter stress, and start plants growing strong during the spring of a dry year.

By Brad Schick

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