Stephen K. Barnhart
retired forage agronomist
Iowa State University Extension and Outreach
Beef cow producers frequently look for ways to maintain or increase pasture productivity. Some of the most practical ways to accomplish this are fertilization, overseeding and improved grazing management.
Pasture fertilization is often not a high priority for beef cattle producers. However, when considering how to carry cows on fewer acres, pasture fertilization may be one of the easiest and most economical solutions.
Do pastures respond to fertilizer and lime nutrients? Yes, particularly to nitrogen.
Grass-based pastures generally respond very efficiently to the first 40-50 pounds per acre (A) of nitrogen (N).
Bluegrass will continue to respond to N applications up to 150-180 lbs/A annually, but at a decreasing rate of response.
Tall cool-season grasses (bromegrass, orchardgrass, tall fescue) respond to N levels of 250 to more than 300 lbs/A, but at a decreasing rate of response.
N recommendations for grass-based pastures are greater than the minimal amounts, but at still modest, yet efficient, rates:
- Early spring (March and April) 60-80 lbs/A
- Late spring (May to early June) (Optional) additional 30-40 lbs/A
- And/or late summer (August to September) (optional) additional 30-40 lbs/A
Tall, Cool-season Grasses
- Early spring (March and April) 80-120 lbs/A
- Late spring (May to early June) (optional) extra 40-60 lbs/A
- And/or late summer (August to September) (optional) extra 40-60 lbs/A
Legume-Grass Mixed Pastures
- If less than 1/3 legume, treat as a grass pasture
- If more than 1/3 legume, no nitrogen is recommended
Note for legume-grass mixed pastures: High or frequent applications of nitrogen (particularly spring nitrogen applications) will make the grass component of pastures more competitive and limit the amount of legumes in the mixture. To encourage a greater legume presence: use modest N rates and limit application to summer or fall; maintain optimum soil pH, P and K levels; improve grazing management, and consider oversowing legumes (interseeding or frostseeding).
Yield responses to phosphorus (P) and potassium (K) are not dramatic or consistent. Forage plants will respond to added phosphorus (P) and potassium (K) when applied to soils with “low” or “very low” soil P and K test levels. Some yield response can be achieved by fertilizing to raise soil P and K test index from “low” or “very low” to at least the “optimum”’ index. Grass responds to nitrogen more efficiently when P and K levels are adequate.
Lime (pH) legumes are more responsive to moderate to high levels of pH than are grasses. For grass-based pastures, try to maintain pH of 6.0 to 6.5. To encourage and maintain legumes, try to maintain a pH of 6.5-7.0.
Test pasture soils to determine lime, P and K needs.
Frostseeding and interseeding, sometimes called oversowing, are all seeding methods used to add more productive or higher-quality forages into an existing sod. Their contribution to stand productivity is much slower than that achieved from nitrogen fertilizer, so expect a gradual production increase. Both grasses and legumes may be added to existing pasture sods. However, the success of this is generally better when done on a thin or less-competitive sod and when follow-up clipping and grazing management are directed at reducing competition from weeds and existing pasture species.
One important step in frostseeding and interseeding is to control broadleaf weeds before introducing legumes into the pasture. When done successfully, added legumes can contribute to the nitrogen needs of the site and lead to similar yield increases that would be seen from moderate nitrogen fertilizer rates. A word of caution, though. The benefits of frostseeding or interseeding may be short-lived, unless grazing management is used to allow for “rest” and expression of the yield potential of the new pasture components. Continuous stocking at high stocking rates will erase any seeding gains within a few years.
Improved Grazing Management
Improved grazing management can lead to some very practical gains in forage and livestock productivity on the same site. For forage plants to express their yield potential, some level of rotation grazing should be practiced that will allow “rest” and recovery of the plants following grazing. By dividing an existing pasture into three to five smaller paddocks and using thoughtful rotation and “rest,” one can increase productivity by 10-15 percent. Dividing and managing six to 10 paddocks can often lead to an additional 5-10 percent in productivity. Some of this increase will be evident within a few months, but realistically, it will take two to three years to reach its full benefit.
For beef-cow producers looking for ways to maintain or increase the productivity of limited pasture acres, there are several practical strategies. Nitrogen fertilizer will give the most immediate increase, but it requires some common sense about rates and timing. Productivity and quality gains can be attained by introducing some new forage species into the existing sod; however, the benefits will occur more slowly and can be easily erased by improper or abusive follow-up grazing management. Longer-term benefits often happen with improved grazing management. Changing grazing management may require some added cost and learning some new skills.
The other two strategies, fertilization and oversowing,can be done in conjunction with improved grazing management for an even faster and more sustained pasture production improvement.