Before attempting to rejuvenate or replace pasture, we must evaluate the pasture or hay field that is in poor condition.
Start by determining the plant species that are present and the number of plants per square foot. Collect information from 10 different locations within the pasture to get a good overview of populations. Also, record the number and types of weeds that are present along with an estimate of the percentage of open soil.
Take 20 soil samples across the field to identify any nutrient deficiencies. At a minimum, split the cores into depths of zero to six inches and six to 12 inches and collect them separately as subsamples for the field. Depending on geographic location and soil type, you may want to take a third core from 12 to 24 inches and include it as the third part of the subsamples to improve the accuracy of the results.
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Split the 20 samples into three groups. Combine one-third of the soil samples into a bulk sample. That reduces the cost of having three composite samples analyzed. When the soil sample results are obtained, the information can help you decide whether to rebuild or replace the forage stand.
The big question
Plant productivity declines when plants are under stress. This is reflected by lower plant populations which reduces yield, increased weed encroachment and presence of invasive species such as Kentucky blue grass (Poa pratensis L.) and quack grass (Agropyrons repens L.).
Evaluating why a pasture or hay field has reduced productivity is the big question. Usually, the problem is caused by multiple factors.
Insufficient amounts of trash or litter on the soil surface result in higher soil temperatures and more evaporation. It also reduces the recyclable nutrients available for plants to use.
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Insufficient amounts of nitrogen, phosphorus, potassium and sulfur reduce plant growth and production efficiencies. Reduced yields, stand longevity, lower protein content in the forage and increased susceptibility to diseases can occur.
There are visual symptoms for top growth that help us diagnose these deficiencies. Tissue sampling during the growing season may also provide answers. It provides a snapshot of what is happening with the plants that are sampled at that point and may not be reflective of what is occurring in the entire field.
Evaluating the root system is also important. Healthy roots should be white. Brown or yellow roots indicate problems exist. Dig out roots, dissect vertically and evaluate their condition.
Drought or a lack of available moisture reduces plant metabolism and photosynthesis.
More abscisic acid slows photosynthesis by closing stoma to reduce water loss from the plant. To compensate for a lack of water availability, root growth accelerates towards areas of higher soil moisture to increase water uptake.
There are usually many factors associated with the decline in pasture and hayland health and productivity. A disease can cause rapid deterioration. But, more commonly, it is management decisions and production practices that cause a slow decline over several years.
Plants should be at least at the three-leaf stage when cows are turned out in the spring. Planning turnout by leaf stage is more accurate than plant height because crested wheatgrass can be four to six inches tall and brome grass eight inches tall at this stage. Turning cows out a day early in the spring reduces fall grazing by three days.
Calculate the carrying capacity of the paddock. Overestimating yield affects the grazing plan and negatively affects stand health due to overgrazing which can damage plant crowns and vegetative tillers that are the starting point for next year’s production. Underestimating yield allows forage to become over-mature which reduces forage quality. Using a grazing stick to estimate the available forage improves accuracy. (see Using the ‘grazing stick’ to assess pasture forage at SDSU Extension).
Know the weight of the animals that are on pasture. On average, cows can consume 2.5 per cent of their body weight in dry feed per day. With high-quality young forage, intakes can be higher than this. Plants in the three-leaf stage contain approximately 85 per cent moisture. A 1,300-pound cow can consume 216 pounds of fresh grass per day. If cow weight is underestimated by 100 pounds, intake increases by 17 pounds a day.
Grazing management is important to improve stand health and increase overall yield. Animals should be moved to a new paddock when there is a minimum of four inches of growth remaining. Some producers follow the philosophy of take half/leave half. Rotational grazing is a management tool that allows plants to rest and recover after a grazing event. Overgrazing removes leaves that are needed to capture sunlight and develop regrowth.
Nutrient reserves in the root system are depleted when plants are overgrazed. Going into winter, having 2.5 leaves on the plant improves root growth, food reserves and tillers needed for next year’s growth.
Record the number of grazing days obtained from each paddock. Compare year-to-year changes in grazing capacity and determine why the production is either increasing or decreasing. A pasture scorecard helps evaluate pasture health and productivity, There are a number of these scorecards available on the internet (see Forage and Rangeland Restoration Reference Guide by Manitoba Agriculture).
Duane McCartney, a retired forage researcher who worked for Agriculture and Agri-Food Canada, conducted research at Melfort, Sask. I have found that “adding 80 lbs. of N and 40 lbs. of P2O5 per acre increased forage production by about 2.5 times compared to the non-fertilized control pasture. The following year we had 1.5 times the forage production as non-fertilized areas.”
A study conducted at the University of Nebraska-Lincoln found that calf weaning weights were increased by one pound for every pound of actual nitrogen applied to the stand.
McCartney also found that reseeding pasture or hayland is a big cost. Another option is to leave the pasture or hayland all summer, then graze it once in the fall. Doing that for a couple of years would bring the pasture back to adequate forage production without breaking and reseeding.
“If a pasture or hayland really needs to be reseeded, we found that growing an annual cereal crop in the field for a year or two was required to get rid of the old dormant grass seeds in the soil. Otherwise, even with treating the field with glyphosate, the stand reverted back to the former stand composition due to the existing seed bank. All our work was on roughland community pastures and we used heavy breaking and reseeding equipment. We seeded meadow brome in some pastures and crested wheatgrass for early spring and late fall grazing in other pastures. These pastures were fertilized on alternate years but eventually the stands reverted back to the original sward due to the old seed bank,” McCartney says.
Managing pastures and hayland is key to keeping the stand productive. Without evaluating what is being done now, existing problems will repeat themselves. There are various sources of information and expertise that can be accessed to help keep pastures and forage stands healthy.
Barry Yaremcio holds a master’s degree in animal science (nutrition) and a bachelor’s degree in agriculture (animal science). He worked in extension for Alberta Agriculture for several years and is now a ruminant nutritionist and production management consultant. Reach him through beefconsultant.com.