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Flood recovery management for pastures

by Dr. Matt Poore, NC State University Animal Science

We have a lot of questions recently about pasture renovation due to damage caused last year by the drought in the western and central North Carolina and the flood in eastern North Carolina. The drought caused stand damage on many farms across the western region, and also in the east on pastures that stayed under water for ore than a week.   As the weather warms up you should be able to tell which fields have severe long-term damage, which are weakened, and which are in good shape. As you assess your pastures, keep in mind that you really need to be thinking in terms of how much bare ground there is, how much of the cover is desirable forage species, how much is undesirable species (weeds), and whether legumes are present. Your local advisors including your extension agents and conservationists have training on assessing pasture condition, so make sure you seek their guidance as you approach your pasture evaluation.

Our initial feedback from local advisors and our observations show that in the west some pastures show recovery and adequate stands, while others show a lot of bare ground, few desirable plants and active erosion. In the east, bermudagrass and bahiagrass that stayed under water for a long time is expected to survive, but fescue or other cool season forages that were flooded in many cases were killed.

Some people think that when the originally seeded forage crop starts to thin out, then the fields need to be completely reseeded. This is not necessarily the case as a pasture ecosystem will naturally evolve over time, and even if you seed one type of plant, eventually you will have multiple species. This is not necessarily bad as long as most of the plant population is of desirable species. On the other hand, if the pasture has a high percentage of undesirable plants, has low yield, little or no legume, and/or has a thin stand with a lot of bare areas then some sort of action is probably called for.

The first consideration is what the main purpose of the forage stand is. If you have multipurpose pastures for grazing and making hay for cattle, then you can tolerate more weeds than if you are trying to make high quality hay for sale to horse owners or other top end hay markets. If you have multiple animal species grazing (cattle and sheep or goats) then the “weeds” might actually have some nutritional value and would not necessarily be undesirable. Finally, if these fields are around your house, or if you just like things to look “clean” then there might be aesthetic reasons for doing some kind of pasture renovation.

If you decide a pasture or hayfield is in suboptimal condition for its purpose and is in need of attention, the next thing to think about is how it got in that condition in the first place. As I indicated earlier, with good management a pasture can remain productive indefinitely, and there is not necessarily a need to periodically renovate. From time to time inputs are needed (like lime and fertilizer), and doing those things on a timely basis will help keep the pastures healthy for a long time. Of course the poor season we had last year was a challenge for pastures, especially if they were overgrazed, but in many cases these pastures will only need rest and a careful look at the fertility program.

The first thing to consider as you approach renovation is soil fertility status. Many pastures that are in poor condition were already in bad shape before the drought or flood and really just need a good fertility program. Start your fertility management planning by doing soil testing. State labs can get the results back to you fairly quickly, and that information is the most valuable tool you have to improve your pastures. Lime, phosphorus and potassium should be applied based on recommendations, and while phosphorus and potassium can go to work as soon as applied, lime will take months to start increasing soil pH. Nitrogen is obviously also a very important fertility input but without desirable pH, and potassium and phosphorus levels at least in the medium range the response to nitrogen will be less that you want.

The second thing to consider is if the problems were caused by poor grazing or hay cutting management. If pastures are undergrazed or overgrazed, pasture condition problems can result. Even with fairly light stocking, if you continuously graze pastures eventually many of the desirable plants will be killed out and undesirable ones will dominate.   If you overgraze pastures, the stand can be thin resulting in a lot of weeds, erosion and loss of yield. That effect is magnified during a drought condition.   No matter what you do to renovate the pasture, continuous grazing management will eventually get you back in the same situation, so couple any renovation efforts with an upgrade in how you manage grazing.

In hayfields, waiting too late in the spring to cut can thin the stand resulting in a lot of bare areas, and that can lead to increased weed populations. Cutting on time before the forage gets rank (early May for most cool season forages in the Piedmont) will help maintain a vigorous stand of desirable plants. Cutting too short is another problem for hayfields, and with disk cutters it is very easy to set them too low and remove too much of the base of the plant. Never cut a cool season pasture shorter than 4 inches or a bermudagrass pasture shorter than 2 inches.

There is no one method of pasture renovation that fits every situation. Once you decide you do need to do something, and take steps to correct management problems that caused the forage crops to get into bad shape, you need to decide how intensive your renovation efforts will be.

I have already mentioned fertility improvement, and any renovation effort should start with soil testing and liming/fertilization. Without that, most other actions will not live up to their potential for improvement.

Some folks think that when a pasture gets into bad shape it just needs aeration. This is based on work that shows that when cattle graze a pasture soil bulk density increases reducing the ability of the forage roots to grow. Most research has shown that aeration alone may give a short-term response, but that in general aeration by itself is not a very effective renovation tool.

Aeration does improve water infiltration and may be of benefit when wastewater is irrigated onto forage crops, and it will also help lime and phosphorus penetrate the lower soil profiles which might help with root growth.   If you know compaction is a big issue, you might consider aeration, but in most cases it is not necessary.

If undesirable plants (weeds) are a problem, then frequent clipping or herbicides should be used. Frequent clipping can work against some weeds, and it certainly makes things look better for a while, but tough weed problems probably call for an herbicide. The problem with herbicides is that without proper timing, they might not get all the weeds that are causing you a problem. They might also cause collateral damage to desirable plants such as clovers. Still, if you have a broadleaf weed problem or a brush problem, the right herbicide applied at the right time can have a big impact.

If the weeds are localized, you might be better to use spot application of herbicides rather than treating the whole pasture. One example of this is the control of multiflora rose by spot spraying or with a granular herbicide that is applied only to the base of the rose bush by hand. The use of herbicides is a complex issue, so I will not give you any specific advice on herbicide use. That is best left up to your personal advisor.

In general, there is not a good way to handle undesirable grasses. If you have a weedy grass like Johnsongrass that is tall, you can use a wick applicator to apply glyphosate. Otherwise, you have to provide optimal management for the desirable grasses present so that they can effectively dominate over the undesirable grasses. One approach is to shift the grass population by changing fertilizer timing.

If warm-season grasses are a problem in cool-season grass pastures, then apply nitrogen only in fall after the warm-season grasses slow their growth, or in the early spring before warm season grasses are growing. If you have pastures that are mostly desirable warm-season species (bermudagrass, dallisgrass, or bahiagrass) don’t apply nitrogen in the spring, but rather wait until early summer (June) and you will shift the stand to the warm-season plants.

One good practice if you have weedy pastures is to add goats or sheep to your farm. They require some extra management, but they do like to eat most weeds over desirable forage crops. If you stock them heavy enough they can make a big difference in the weed populations in your pasture.

Once the weeds are under control, or if you have a good stand of grass with no clover, then you should seriously consider seeding clover or other legumes into the pasture. Clovers can be drilled in the fall or spring as long as the pasture is grazed periodically to allow the seedlings a chance to develop.

You might also have success with surface broadcast seeding of clover in late winter (also known as frost seeding). Clovers will only do well if pH is above 6.0, fertility is right (especially phosphorus), and if pastures are grazed pretty close to allow the seedlings to develop without a lot of competition from grass. As you read this in March it is really too late to frost seed (except at high elevation in the mountains) but keep that practice in mind for next winter to fill in thin stands of grass.

The ultimate in pasture renovation would be to completely establish a new stand. If you decide your pastures are so bad that you need to go to that extent, you need to be aware that this is a costly approach. Based on our forage budgets it costs close to $250/acre to totally establish a new pasture. You also have to figure that you lose nearly a full year of production due to the need to allow the plants to establish. Reseeding pastures without reducing animal pressure will in most cases lead to failure to develop a good stand.

If you decide that a cool season pasture must be reseeded completely, you will have to wait until fall to seed if you want your efforts to be successful. The options you have in May are; 1) to get the most you can out of the existing forage present and keep weeds under control, or 2) kill the existing stand and plant a summer annual (generally millet or sorghum-sudan). If you are short of forage for the number of animals you have, then the warm-season annual may be your best choice. Just remember, once you reseed the pasture you will have to do something to reduce the animal grazing pressure for the establishment year.

Seeding can be done either using complete tillage or no-till techniques. If fertility on a site is low, deep tillage after lime and phosphorus application is a good idea. If there are a lot of weeds present in pastures or hayfields, you must be aware that there is also a large viable seed bank present. If you till the soil and plant a forage crop, you will also get a good crop of weeds. If you are going to replant you are well advised to get the weeds under control several years before going to the effort of developing a new stand, or be prepared to spray for weeds that may compete with the new forage plants. In many cases, especially in the mountains no-till is your only option due to a very high potential for erosion.

If you do reestablish (or if you establish forages on old cropland), make sure that you use the best quality seed available. There are many new forage options for you including non-toxic endophyte infected fescues (MaxQ, MaxQ2, BarOptima, etc) that have great potential, and there also are new orchardgrass varieties (e.g. Persist) that are available where orchardgrass is called for. These new varieties and the many other good forage varieties available can lead to improved pasture and animal performance and should be considered if you go the great effort and expense of establishing new stands. I would not recommend establishing endophyte infected fescue unless you currently have less than 1/3 of your acreage in fescue, or if you are in a heavy use pasture such as a bull lot, horse pasture (for non-reproductive horses) or some other kind of feeding/holding pasture.

We are seeing renewed interest in legumes due to the high cost of nitrogen. If you are a very crop oriented farmer then alfalfa might be a good option if you have soils to which it is adapted. White clover is an excellent pasture plant that fixes a lot of nitrogen, and red clover works very well on hayfields. Unfortunately most herbicides will kill legumes, so if you have a weed problem you need to get that under control before you work to establish clover. The best time to establish these legumes either in existing stands of cool-season pastures or in conjunction with establishing cool-season grasses is in the fall.

The final word as you approach pasture or hayfield renovation is to use common sense. Poor fertility and overgrazing are often the “root” of the problem, and you need to correct that no matter what you do. Herbicides can help if you make the right choice for the weeds you have and apply them at the right time. Generally, pasture condition problems result from poor pasture management in general and if you don’t improve your management in concert with the renovation, you are destined to have problems again in the near future.

Usually, a combination of the less aggressive practices, including fertility improvement, use of a selective herbicide to get the problem weeds, reestablishing the legume stand and then improving grazing and hay cutting management will yield big results. Next month we will discuss in more detail the steps you need to take in Spring and Summer in preparation for an Autumn planting of a cool-season perennial pasture.

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