Grazing Management Q&A
University of Missouri forage and grazing experts Rob Kallenbach and John Lory take on common questions from farmers and ranchers about pasture fertility and grazing management.
Q: When is the best time to fertilize pastures?
Kallenbach: The first question to answer is whether you even need the extra forage from fertilizer. Research says you can get about an extra 20 pounds of forage production per acre for every pound of nitrogen (N) you put out there, up to about 100 pounds. If you get the full effect of 100 pounds, it would be worth an extra ton of forage per acre.
I’d be careful about overapplying N in the spring. For many farms, grass grows lush then anyway, and fertilizer gives you more growth than you can manage. When you stimulate cool-season grass growth in the spring, its competitive and shading effects can crowd out legumes like clover. If you fertilize in August, you might get more fall growth when you can use it.
I recommend that you put about one fourth of your fertilizer on in the spring for early grazing and maybe another fourth in May or June to extend good forage into summer. Then apply the rest in late summer to help extend the grazing season as far into fall as possible. That’s better use of your fertilizer dollars.
Q: What’s the right mix of legumes in a pasture?
Lory: Legumes are good for their grazing quality, and they fix N on their roots, which helps the surrounding grass plants, too. Up to 50% of the N in grass from a legume-grass mix is fixed by the legume and transferred.
We like to see 30% of the plants in a pasture as legumes such as red clover, lespedeza, or bird’s-foot trefoil. It’s a good thing to have two or more legumes in the pasture mix to reach the 30% goal. A complex mix of species seems to give more stable yields.
Your eyeball is not necessarily the most accurate way to estimate clover percentages; you will have a tendency to overestimate the legume.
Q: Last summer and fall it was very dry. Did I waste my pasture fertilizer?
Kallenbach: In the tests we’ve done in dry weather, we don’t get as much effect from fertilizer. Remember that forages grow longer than annual crops. In Missouri, we can have forage growth all the way into December if the weather cooperates. Fertilizer that doesn’t get utilized in the fall tends to carry over into the spring in pastures.
Lory: Fertilizer carries over in forages better than grains because of the lower potential for saturated soils. Forages have extensive root systems that build organic matter in the soil and promote aeration.
Q: Is red clover the best pasture legume?
Kallenbach: Yes, I’d say, in general, but clover doesn’t do much when it is really hot; it goes dormant. Lespedeza is a better legume at that point, but it will only fix about as much N as it uses itself, and not much is left for the surrounding plants. As with most things, it’s a trade-off. A mix of pasture forages is best for a variety of reasons.