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Spring and summer grazing in 2024

Craig Sheaffer, Extension forage agronomist, Krishona Martinson,  Extension equine specialist, Troy Salzer, Extension educator, David Nicolai, Extension educator-crops, and Kabita Poudel, UMN graduate student

Key points

  • Above normal early spring temperatures followed by precipitation will lead to rapid pasture regrowth as air temperature rise.
  • Grazing of tall and short growing grasses and legumes should be delayed until minimum heights of 8-10 and 4-6 inches, respectively, are reached to allow for recharging of plant energy reserves.
  • Following initial grazing, mostly grass pastures should be rested for a minimum of 2 weeks or until regrowth to 8-10”
  • Planting of warm season grasses like sudangrass grass and sudan-sorghum hybrids is a strategy to provide summer forage should drought occur.

Pasture regrowth

Regrowth in spring after grazing forage grasses and legumes is described by a general growth curve (Figure 1). Initial forage yield is low because plant energy reserves (carbohydrates) and leaf area are small (Figure 2). As leaf area increases, photosynthesis recharges root energy reserves, and root and crown mass and tillering increases. Forage yield increases rapidly until flowering as the proportion of stems in the forage increases and flowering begins. At flowering stages, stored energy reserves have been recharged, and following harvest or grazing, the plant can experience more rapid regrowth. In most of Minnesota, grasses and legumes typically begin flowering in late May in response to increasing day length (photoperiod).

Figure 1. Relative changes in grass forage yield and quality with increased maturity. Often, harvesting or grazing at or just before stem elongation is a compromise to balance forage yield and quality. For hay making, grasses are typically harvested between the boot and flowering stage of maturity.

Figure 2. Changes in relative carbohydrate reserves in crowns, stem bases, and roots from leafy to flowering growth stages. Spring regrowth is dependent on stored carbohydratesthat are replenished by photosynthesis once leaves emerge.  

 Above average air temperatures in late winter 2024 led to early green-up of pasture legumes and grasses. This was interrupted by a cold period followed by much needed precipitation. Now leafy vegetative growth will resume and continue till flowering in mid-late May. With normal spring rainfall, this should provide extra grazing time this year. Every year it is important to consider routine pasture management practices, such as rotational grazing, and to observe recommended pasture stocking rates to sustain and improve pasture productivity. These are described at:

What should we do differently this spring?

Because of this year’s unique weather, it is important to emphasize several management principles.

Delayed grazing

Even though grass and legumes will “green-up” earlier than expected this year, resist putting animals on pastures until grasses and legumes have enough growth to begin replenishing carbohydrates reserves used during the winter (Figure 2). Grazing should be initiated only when a significant amount of foliage has accumulated and carbohydrate energy reserves can be replaced by photosynthesis. Grazing should be stopped before all leaves and stems are consumed and minimum residual heights observed (Table 1). 

Table 1. Average heights to begin and end grazing of pastures with tall- and short-statured grasses and legumes.
Species Starting height Stopping height
inches inches
Tall grass and legumes
 > Orchargrass, tall fescue
 > Alfalfa, red clover
8-10 3-4
Short grasses and legumes
 > Kentucky bluegrass
 > White clover
4-6 2-3

 Overgrazing in the early spring will deplete carbohydrate reserves, slow regrowth, weaken plants, and reduce yields later in the season. Root and rhizome growth (underground stems) will be affected and thin stands can be exposed to weed invasion. Early grazing of pastures with both short and tall growing grasses will encourage growth of short species like Kentucky bluegrass that can withstand repeated grazing but which are less productive on an annual basis than tall growing species. For plants stressed due to winter injury or soil heaving, longer spring growth periods will be beneficial to plant persistence.

Additionally, hoof traffic by livestock in the early spring can lead to soil compaction and be detrimental to stand density of legumes and bunch grasses (e.g., orchardgrass, meadow fescue) because root systems may also be weak or displaced by freezing or thawing cycles of the soil.

As typically recommended, be cautious about the first introduction of cattle to pastures containing the succulent forage of clovers and alfalfa because grazing may cause bloat. A caution approach is to limit initial grazing to about an hour the first day with increasing grazing times each day. It is also advised to feed hay so that the rumen is partially full. This will allow microbial population in the rumen to adjust. Likewise for horses a slow introduction to cool-season pasture is recommended to reduce the chance of illnesses due to high levels of non-structural carbohydrates in the forage.

Rest periods

With early spring grazing, maintaining rest periods and observing plant residue minimums before re-grazing is especially important. Continuous grazing of plants and removal of too much foliage will not allow plants to recharge energy reserves. In a spring with adequate moisture and ideal temperatures, rest periods as short as 14 days are adequate for cool season grasses to reach ideal regrowth heights. During summer, rest periods of at least 30 days are common to reach the same plant regrowth heights. For alfalfa-grass mixtures, rest periods should be about 3 to 4 weeks because alfalfa (and red clover) is more prone to depletion of root reserves. For plants stressed due to winterinjury or drought, longer rest periods will be beneficial to plant persistence.

Weed control

Solid stands of vigorously growing grass and legumes will suppress weed invasion, but weeds will invade overgrazed or abused pastures. In those cases, weed control is recommended to reduce weed competition with pasture grasses and to increase pasture productivity. This year’s early spring will allow an extended period of time for annual weed control before initiation of grazing. 

Spring is a good time to control annual weeds with either an herbicide or with mowing. Fall is the ideal time (August 1 – September 15) to use a herbicide to control perennial weeds. If using an herbicide, always follow the directions and grazing restrictions listed on the herbicide label. Keep in mind that herbicides cannot be used on grass-legume mixed pastures. Herbicides used to control broadleaf weeds will also kill legumes. In grass-legume pastures, best management practices (e.g. resting, mowing, fertilizing, etc.) that give the competitive advantage to pasture species are the main source of weed control.

Soil fertilization

Soil testing and applying fertilizers according to recommendations is as a way to increase pasture productivity. Application of P, K, and S are especially important to legume yield and persistence, while N is critical for grass productivity. Fertilizer application rates should be based on pasture yield potential. For N fertilization of pastures, a split application is recommended with at least half being applied in early spring to stimulate overall plant growth and yield. For more information, see Fertilizing hay and pasture grasses.

Plan now to reduce summer feed shortage risks

For the past several years, summer droughts have greatly reduced mid-summer pasture productivity. This year despite the recent snowfall, we are again facing soil moisture deficits in many regions of the state, as seen in the drought monitor

While weather patterns are unpredictable, it may be prudent to reduce the risks of forage shortages this summer. For pasture, establishing warm season annual grasses for use in mid-summer should be considered. Examples of warm season grasses that can be grazed multiple times are shown in Table 3. Sudangrass and sorghum-sudangrass, and pearl millet have been consistently among the highest yielding grasses; however, the risks of nitrate and prussic acid poisoning in sudangrass and sorghum-sudangrass need to be managed. These grasses are typically planted in late May to early June when soil temperatures reach 50 F and can be grazed about 5-6 weeks after planting at a height of 18-24 inches. For quick regrowth, 6-8 inches of stubble should remain. Grass yields and crude protein content are greatly affected by nitrogen (N) fertilizer rates. With increased N fertilization, both yields and crude protein concentration should increase. Also, with increased maturity, forage quality will decrease.

Table 2. Potential forage yield and forage quality of warm season annual forage grasses when subject to multiple harvests and fertilized with 100 lb/acre of nitrogen.
Crop Yield CP* NDF* IVDMD*

T/A % % %
Sudangrass 6.2 19 60 63
Sorghum-sudangrass 5.8 20 59 65
Teff 3.5 17 60 54
Pearl millet 5.7 19 58 65

*CP=crude protein; NDF=neutral detergent fiber; IVDMD=in vitro dry matter digestibility

These annuals might be a way to increase pasture productivity especially if your pastures were over grazed the last few summers and might have a high percentage of low productivity grasses like bluegrass. The use of annuals also can allow you to renovate these pastures, getting weeds under control, providing multiple benefits in the process.

For more information on warm season grasses, see the following:

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