Pasture Management: Optimizing Grazing and Fertilization

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Shelby Gruss
Assistant Professor, Forage Extension
Iowa State University Extension & Outreach 
sgruss@iastate.edu

 

As spring heralds, the revival of our pastures, managing them effectively is crucial for both short-term productivity and long-term sustainability. Understanding when to begin and stop grazing and how to fertilize efficiently is critical to optimizing pasture use. Many parts of the state have started grazing, but grazing management is not only deciding when we start but how we graze throughout the season.

Grazing Management

Cows grazing in pastureBefore letting livestock graze, assess if the pasture is ready. Grazing too early can stress pastures, especially those recovering from multiple years of drought conditions. For rotational grazing systems, animals can be introduced when the forage reaches about 6 inches, whereas continuous stocking should wait until 8-10 inches. Spring rotations should be quick, grazing down to 3-4 inches and moving, to keep pace with growth and promote vegetative growth.

As we progress into summer, our cool-season pastures will begin slowing their growth and go through the “summer slump.”  We can start slowing our rotations, giving the forage longer rest periods to recover during this time. Other opportunities include incorporating warm-season annuals or perennials into your rotation. These will produce well during the high heat of the summer months, supplying additional forage when your cool-season pastures are limiting. Warm-seasons need to be managed differently than our cool-season pastures if we want maximum production. Wait to graze till the plants are taller than 18 inches, and stop grazing at 6 inches. This will help enhance regrowth for another grazing cycle. 

Fertilization Strategies for Pasture Health 

Fertilization is equally essential. Soil testing is the best method to determine nutrient needs, providing a complete assessment for adequate fertilization. A sound program should include appropriate amounts of nitrogen (N), phosphorus (P), and potassium (K) tailored to the forage within your pasture. In pastures, cattle recycle about 80% of the P and K through manure and urine, helping maintain soil fertility. This is why it is recommended to only soil test every three years, whereas in row crops, it is recommended to soil test every year. PM 1688 article “A General Guide for Crop Nutrient and Limestone Recommendations in Iowa” by Iowa State University is a helpful tool in determining fertilization rates for your goals.

Nitrogen moves more quickly through our soils, so maintaining a good N fertilization program is important, particularly for grass-dominated pastures. Pastures with more than 30% legumes on a dry matter basis do not have to fertilize with N, and the legume fixates N and will supply some N to the grass. Applying 25-50 lbs of N per acre after each grazing cycle in grass-dominated pastures can boost forage productivity throughout the season. If following each rotation cycle is impractical, a split application in spring (30-60 lbs N early and 40-60 lbs N late) and a final application in late summer (40-60 lbs N) can help boost productivity. However, an early spring N fertilization before the spring flush can enhance productivity when the forage is already producing at a high rate, spring flush. This can lead to excess forage and waste. 

A few considerations that can be made:

  1. Skip the early spring N fertilization.
  2. Set aside an area to be mechanically harvested for stored feed.
  3. Stockpile the excess forage for the summer months when growth is declined.

PastureStockpiling is a good option, but if this is your chosen approach, know this will be low-quality forage as it has had time to mature, so do not utilize it on your animals with high nutrient requirements. Also, this is not recommended with toxic endophyte tall fescue as the endophyte concentrates in the seed heads. 

Another stockpiling opportunity is going into the fall. A late summer N application is essential for fall stockpiling. Unlike stockpiling for summer, tall fescue is a great fall stockpiling opportunity. It will only produce a seed head once throughout the season. 

Seasonal adjustments might be necessary, especially in regions affected by drought or other climatic challenges. An additional application of N early in the spring can help kick-start growth, particularly in slow-greening pastures. 

Similarly to our cool-season forages, our warm-season forage needs fertilization. Again, soil testing will be valuable in assessing how much P and K are required. N application (50-60 lbs) for our warm-season perennials is recommended in late May, right before the grasses begin growing quickly. An additional split application following the grazing cycle can help boost regrowth. A similar pattern would be conducted in warm-season annuals, except N application should occur at planting and again following grazing to stimulate the regrowth.

Lastly, when soil testing, assess your pH. Most of our forages prefer a neutral pH of 6.0 -7.0; some, like alfalfa, need 6.5 -7 for maximum production. Knowing what forages you have and what pH that forage can withstand will be important in maximizing productivity and persistence for multiple years.

Overall, successful pasture management involves careful timing of grazing and strategic fertilization to maintain healthy, productive pastures that support livestock and sustainable agricultural practices.

- Photo credit: Jason Towers

 

Date of Publication: 
May, 2024