soil testing

While summer may be over and the main grazing season concluded, the fall is one of the best times of the year to evaluate the condition of your pasture and complete pasture management tasks that will pay dividends the next grazing season. Spend some time now before it gets cold preparing your pastures for spring growth.

Soil Test– After a summer of grazing, fall is a great time to take soil samples to check and see where you stand on soil pH, nitrogen, phosphorus and potassium. This is important information to have when making management decisions such as how much fertilizer or lime to apply and if your pasture needs to be renovated. It also allows to apply what is needed to avoid over application which can have negative environmental impacts with runoff and leaching and also result in unnecessary spending. Testing should be done routinely every 2-3 years or prior to undertaking a partial or full pasture renovation. The University of Delaware offers soil testing as well as several private labs including Agrolab in Harrington.

Assess- Take a walk through your pasture. Observe and inventory what desirable pasture species are present, the ratio of grass to legumes, the types of weeds present, the stage of maturity of desirable species and weeds, how much bare soil there is and possibly use a compaction meter to see what the soil compaction levels look like from hoof pressure after a wet growing season.

Weed Control- The fall is a great time to do some weed control. Perennial weeds such as horse nettle, dogbane and thistle respond well to fall herbicide applications (as long as it hasn’t been too dry) because they are translocating energy to store in their roots in preparation for overwintering. Herbicides should be applied according to label instructions and prior to the first frost. The Mid-Atlantic Weed Management Guide is an excellent regional resource and has a chapter devoted to forage weed management: http://extension.udel.edu/ag/weed-science/weed-management-guides/

Lime- Based on your soil test results, apply lime in quantities to increase soil pH appropriately. Over time without the application of lime, soils generally become more acidic. The addition of certain fertilizers such as ammonium sulfate can also make soil more acidic. Acidic soils make nutrients less available for pasture species to uptake. Most pasture species prefer a soil pH between 6.0-6.5. Raising soil pH not only makes nutrients more available to pasture grasses and legumes for uptake but can also make soil bacteria more active which helps to release nutrients. Based on your soil test results you will apply either high calcium lime or high magnesium (high mag) lime depending on your needs. Additional recommendations for liming pastures can be found here: http://extension.udel.edu/factsheets/forage-and-hay-crops/

Fertilize– Based on your soil test results, and provided there is adequate soil moisture, apply nitrogen (N), phosphorus (P) and potassium (K) as needed. Soil test results allow you to apply the correct amounts of fertilizer needed which saves money and avoids over application. Fall is widely recognized as one of the best times to apply fertilizer. Fall applications of fertilizer help pasture stands to be hardier, overwinter better and be more productive in the spring. Phosphorus helps with root growth and development which in turn helps with pasture persistence and longevity of a stand. Potassium functions much like anti-freeze in a plant and assists it in coping with hot dry or extremely cold weather. Nitrogen provides for leaf growth and development and fall applications of nitrogen help boost pasture production the following spring. Fall applications should be completed by early November. Remember that Delaware nutrient management laws do not permit commercial fertilizers to be applied between December 7 and February 15. Additional recommendations for fertilizing pastures can be found here: http://extension.udel.edu/factsheets/forage-and-hay-crops/

Mow/Drag– Mowing pastures promotes more even growth after a summer of grazing and can assist in weed control by clipping weed seed heads before they are viable. Pastures should be mowed no shorter than 3-4 inches to allow enough residual plant material for pasture species to store energy reserves for the winter. Dragging a pasture spreads manure more evenly then a cow or horse will. It also offers some benefit for internal parasite control by exposing parasites and their eggs to sunlight and desiccation or drying.

Rotationally Graze or Strip Graze- Develop a grazing plan based on your visual evaluation of your pastures to rest and rotate your pastures. Divide your pastures into smaller areas to reduce selectivity and force animals to graze more evenly if you find that forage is becoming too mature and being wasted in some areas of your field and overgrazed in others. Pastures should never be grazed less than 3-4 inches as it causes stress to the plant because they begin to use their root reserves instead of using their leaf material to produce more energy for growth. If a pasture is continuously overgrazed eventually the desirable pasture species utilize all of their root reserves causing them to die and leave bare spots in the pasture. Rotational grazing gives pastures a must needed rest in between episodes of grazing. The length of time regrowth between grazing episodes is dependent on environmental growth conditions. Strip grazing is a type of rotational grazing and is a great technique for rationing pasture during times of less growth such as winter months. Animals are offered a portion of a field to graze and then are moved on a regular basis once that area is consumed. This is generally high intensity grazing for shorter periods of time.

Overseed/Reseed- Fall is actually the best time of the year to reseed a pasture. Seed germinates faster as soil temperatures are warmer than in the spring. Pasture seedlings get several months of a head start on spring weed growth which makes them able to compete better in the stand. If the existing stand simply needs thickening, then overseeding is a good option. If soil pH and fertility need dramatic adjustments, soil compaction is severe, weed pressure is heavy and desirable pasture species are thin then a full renovation with conventional tillage is probably in order. A common mistake is grazing newly renovated pastures too soon. Plants need time for strong root development so they aren’t pulled out by grazing animals or damaged by hooves. Full renovations require a good year of careful mowing, etc. prior to grazing animals being turned out. If you do not have the room to wait a full year, but still need a full renovation, considering breaking your pasture into sections, seeding one section per year. This way, the new section will be ready for animals as you prepare to renovate the next section the following year. This also helps with expenses, since full renovations can be costly.

Stockpile-Tall fescue grass pastures offer the ability to stockpile or grow forage and store it in the field to be grazed in late fall or winter. Tall fescue is uniquely suited to this practice as it actually maintains nutritional content and increases in palatability to the horse after the first frost. In order to stockpile tall fescue in the field for later grazing, an early fall application of nitrogen to stimulate leaf growth is necessary. Wait to graze until late fall or winter and consider utilizing strip grazing to maximize the utilization of stockpiled tall fescue.

Choose the Right Forage Species– This is one of the most costly inputs for pasture, yet is also the most important choice you can make for your pasture. Unfortunately, we do not share the same climate as Pennsylvania, Kentucky, or Western Virginia, which provide excellent conditions for perennial, cool season grasses. Our warm, humid environment tends to stress cool season grasses during the summer months, reducing the longevity of some species such as orchardgrass, timothy, and perennial ryegrass. There is an exception-tall fescue, particularly varieties containing the friendly (novel) endophyte, which tend to persist much longer when established correctly. Please note these are different than endophyte-free varieties, which tend to have less vigor. There are many pasture mixes available on the market so be sure to do your homework and be familiar with what is in the mix you are being sold or consider a custom mix of appropriate species for our growing conditions.

In conclusion, fall is a great time to evaluate your past grazing season. Think back- did you have times where pasture growth was in excess of what was being utilized by grazing animals? A time of deficiency? How can you overcome those times in the future? What did your pasture look like by the end of the summer? Often times when asked to make recommendations to help producers manage their pastures more effectively, we discover that pastures are greatly overstocked and continuously grazed. Even when you follow good management practices, pastures that are overstocked will result in overgrazed, damaged stands that do not persist. Weeds are opportunists and bare soil allows them to germinate from existing soil reserves or propagate if they are not controlled. If you do not already have one, consider establishing a sacrifice lot or a place to put animals and feed hay when pastures cannot be grazed for a variety of reasons (too wet, too dry/droughty, no growth, when a pasture has been recently seeded or fertilized, or it is too cold and limiting growth rates). This practice will help extend the useful lifetime of your pastures. Hoof pressure on wet pastures in the winter damage the desirable plants and result in soil compaction. Pastures that are grazed year round are less productive and need to be reseeded more often.

Susan Garey, Extension Agent Animal Science and Phillip Sylvester, Kent County Agriculture Agent

University of Delaware

Part 1: The Pre-Planning Process…

Over the years since I first came to Delaware, I have received numerous requests concerning overseeding or renovating pasture and hay fields. Unfortunately, these requests usually come about just before someone wants to actually plant. In reality, producers should begin considering the process as much as a year ahead of the actual time that they want to plant a field. Since our fall plantings of forage crops seem to perform better than spring plantings, it’s a good time to begin a discussion of the process. Often, we find ourselves moving into mid- to late-fall without having taken the time to really consider all decisions that have to go into improving the odds that the planting will be successful. Seed costs alone can equate to more than a hundred dollars per acre in investment expense; and, if we really take into account all the variable costs, a new pasture or hay field can easily represent an investment of hundreds of dollars per acre.

So in the pre-planning process, what’s first? I know many get tired of hearing the phrase but testing the fertility of your soil far ahead of time is still the number one issue. The proper sampling depth is 0 to 4 inches in fields where you will be using a no-till drill to seed the forage and on fields that you do not plan to use deep tillage and have not been applying significant quantities of commercial nitrogen (N) fertilizer. In these instances, you will not be incorporating lime to neutralize acidity from the N fertilizer or incorporating large amounts of phosphorus [P or (P₂O₅)] or potassium [K or (K₂O)] fertilizer. Your expectation is that the soil test will indicate that the soil pH is in the 6.0 to 6.8 range and the P and K levels are in the medium to optimum range. If your expectations do not prove true and the pH is low enough to require several tons per acre of limestone or the P and K levels are low to very low and the fertilizer and lime needs to be mixed into the soil thoroughly, you will need to change plans and consider some type of tillage to incorporate fertilizer and/or lime.

If you have used large quantities of commercial N fertilizer in the past, you really should take both a 0-2 inch depth sample for determining the soil acidity in the upper soil layer as well as a 0 to 4 inch depth sample for nutrient content (phosphorus, potassium, calcium, magnesium and other essential elements). If you are unsure when limestone was last applied to the field, sampling both depths is a good approach since it will provide you with more information about the nutrient status of your field.

The reason for this distinction is that the ammonium or urea N forms that are applied as fertilizer are converted by soil bacteria into nitrate through a process called, nitrification, In this process, the soil bacteria oxidize the reduced form of N and release hydrogen ions that cause the soil to acidify. Since the N is all surface applied, the release of acidity near the soil surface can create a condition known as ‘acid roof’ where the top inch or two of soil is much more acidic than the deeper layers of soil. A second reason involves the very slow movement of limestone down through the soil. Studies on pastures in Connecticut many decades ago showed that lime moves downward at a rate of about 1 inch per year. Therefore, it takes a very long time to have an impact on the entire rooting zone of the forage grasses and legumes.

In fields where tillage is planned prior to establishing a forage crop, the traditional plow layer sample (0 to 8 inches) for both soil pH (acidity) and essential nutrient status is the appropriate choice. If the soil sample indicates that the soil must be limed, apply the recommended amount of limestone and work it into the soil as soon as possible to allow time for the limestone to neutralize soil acidity before planting time. If the weather after lime application and incorporation remains dry, the limestone will not completely dissolve and neutralize the soil acidity. I recommend that producers take a second soil test before planting in late summer or early fall to determine if any additional lime is needed. Additional agricultural lime and the recommended P₂O₅ and K₂O fertilizer as well as any other needed nutrients can be applied and worked into the soil shortly before planting the field.

Everyone asks the question of whether to apply N at the time you plant a new field or seed a field you are renovating. My preference is that you should wait until the new grass is several inches tall and has enough biomass and roots to compete for applied N and store any extra N for future growth. Very small forage seedlings use and need very little N, no more than a couple of pounds N per acre, until they reach 2 to 4 inches in height. Often the residual N from organic matter mineralization during the summer, will supply the small amount of N the seedlings require. Once the forage plants have enough leaf area to capture the sun’s energy and convert it into more plant tissue or into sugars for storage, the demand for N will increase significantly. When forage seedlings are very small, weeds or current vegetation in renovated fields are likely to be better able to compete with new forage seedlings for N, light, water, and other nutrients. Although annual weeds and/or current vegetation will be present when N fertilizer is finally applied to the new seedlings, the perennial forage seedlings will be in a better competitive position to compete for the components needed for growth and establishment. Summer annual weeds that germinated with the forage crop will be killed at the first fall/winter frost and provide the forage plants with more space, sun, water, and nutrients.

In the next installment, I’ll cover the question we most commonly receive, “What should I plant?”

This article was submitted by Dr. Richard W. Taylor, Extension Agronomist, University of Delaware. Dr. Taylor can be reached at rtaylor@udel.edu

Fall Pasture Management Tips

Is It Time to Think about Renovating or Planting a New Pasture or Hay Field? Part 1