Fall alfalfa management in 2024

Craig Sheaffer, Extension forage agronomist

Excess rainfall in the spring followed by late summer drought has made for another challenging year for growing alfalfa. Earlier we reviewed some strategies to deal with the wet spring conditions. See: Alfalfa news in summer of 2024 . Now we are in mid-fall and some new questions arise:

Will drought this fall harm alfalfa?

Minnesota’s alfalfa growing regions have had variable levels of drought this fall combined with above normal air temperatures. The drought will not lead to increased winterkill of alfalfa. Fall moisture deficits actually increase winter survival compared to well watered conditions. Irrigation is not necessary. The longer growing season is favorable for the dormancy reaction and accumulation of energy reserves which should reduce risk of winter injury. See  Fall cutting of alfalfa in 2023 for more information.

Is it now safe to fall harvest?

It is a safe time to harvest. Although we have not reached air temperatures of 24F that normally kill the foliage and suppress regrowth, there are not enough growing degree days or time left for alfalfa to regrow. Regrowth in the fall stimulated by September and October harvests will use carbohydrate reserves and weaken the plant going into winter. However, if alfalfa is harvested in November it is important to leave at least a 6-inch stubble on fields to reduce risk of winterinjury. Alfalfa stubble in the fall is beneficial to insulate the overwintering crowns. Stubble catches and holds snow which insulates the soil surface.

Does residue in the fall affect spring forage quality?

There is potential for overwintering residue (dead stems) to reduce spring forage quality depending on the residue amounts. Plants that are left in the fall will lose their leaves and by the spring only dead stems remain. If normal winter conditions occur, these stems will be mostly lodged and not picked up at the first harvest. But in years without normal snowfall, the stems can still be standing in the spring. 

This spring we sampled seven alfalfa fields in north central Minnesota to determine how overwintered fall stems affected spring forage quality. We harvested the spring forage regrowth including the dead fall stems, and then separated the two fractions. Table 1 shows the first harvest forage quality of spring plants (spring whole plants without dead stems) and overwintered dead stems from the previous fall (fall stems) when alfalfa was harvested at bud. Stems from the previous fall had significantly lower crude protein (CP) and fiber digestibility and higher neutral detergent fiber (NDF) than the spring forage regrowth without stems. Harvesting the spring forage including fall stems reduced the overall spring forage quality. Dead stems compromised about 10% of the total spring biomass (dead stems plus herbage regrowth). 

Table 1. Crude protein (CP), neutral detergent fiber (NDF), and fiber digestibility of alfalfa plants without fall stems, fall stems alone, and combined spring plants and fall stems when harvested at bud stage. 

Plant part	CP	NDF	Fiber Digestibility
	%	%	%
Spring plant forage	23	37	63
Fall stems	6	76	20
Spring plant + fall stems	22	41	59

 During the winter of 2023-2024, we had less than normal snowfall; in a normal winter with more snowfall, we would expect to have less upright dead stems in the spring. In years with significant amount of standing overwintering dead stems, growers can increase the first cut quality by mowing the dead stems in early spring before alfalfa regrowth.

Will residue left in the fall lead to rodent damage in alfalfa?

Gopher mounds in alfalfa have destroyed this stand.

Many rodents use alfalfa stands for overwintering, but the primary potential damage is from pocket gophers, an animal native to Minnesota. Gophers have ecological benefits in prairies but can cause havoc in pastures and alfalfa fields. Gophers create an extensive tunnel network from 1-2 feet deep and establish food storage dens located deeper in the soil. The soil excavated during tunneling processes is deposited above ground in mounds about a foot in diameter. Gophers feed on alfalfa roots and crowns and can weaken and kill plants. In addition, gopher mounds can affect alfalfa spring regrowth, damage harvest equipment, and increase the ash content of the forage. With the mild weather and soils not frozen, gophers are still active and soil mounds can be hidden in unharvested alfalfa fields. In many areas, gopher control specialists can be hired. Gophers and gopher control is described in  Pocket gophers.

Will my alfalfa seeded in late August and early September make it through the winter?

It depends on whether seeds have germinated and had adequate development before freezing temperatures. Air temperatures have been above normal but low soil moisture levels have often prevented germination. Plants with a high probability of survival will have at least four trifoliolate leaves and developed a crown through contractile growth. Unfortunately, if drought conditions have delayed germination of seeds until after early September, seeds have little chance of developing into plants that survive till spring. Alfalfa can germinate at temperatures as low as 32 F although it can take 2 weeks for germination. Seeds that do not germinate in the fall can still germinate and grow in the early spring but these are still at risk of freezing. See Drought risks to late summer alfalfa seedlings for more information

Is it too late to soil sample and fertilize?

If the soil is not frozen, soil sampling and fertilizer application can occur on most soils. For alfalfa establishment in spring of 2025, fall incorporation of lime is ideal because it takes time to react with in the soil and change the pH. Nutrients such as phosphorus (P), potassium (K), and sulfur (S) can be applied in the fall. However, because of potential leaching,  K and S should not be applied to sandy soil in the fall. For more information on alfalfa fertilization recommendations see Fertilizing alfalfa.