Under irrigation, the use of fertilizer becomes much less risky as timing and amount of water applied can be managed. The potential for optimizing forage yields is very high as nutrient and moisture status can be controlled more closely as compared to dryland conditions where the outcome is dependent upon rainfall.

Research at the Western Beef Development Centre at Lanigan, SK found that, in general, response of tame pasture to application rates less than 50 lb/acre of actual nitrogen (N) tends to not cover off input costs. Therefore, depending on soil test results, rates of greater than 50 lbs/acre are likely required. Additionally, evaluation of four nitrogen application rates on tame grasses found that the greatest yield response to nitrogen was seen at a rate of 100 lbs/acre of actual N. At rates greater than 100 lb/acre actual N there was no added yield benefit.

A study conducted in western Quebec evaluated yield response of forage stands dominated by timothy and orchardgrass to four rates of N fertilizer⁶. On average, 112 lb/ac (125 kg /ha) of actual N was necessary to reach the optimum economic yield under the site conditions which included relatively cool soil conditions that likely restricted soil N mineralization in early spring. This shortage of soil N had to be compensated for by additional fertilizer to reach the optimal economic yield of these forage grasses.

Both of the above examples from different regions of the country present very generalized guidelines and emphasize the importance of evaluating each site, including soil conditions and forage types. In all cases, a soil test is needed to determine the optimum application rates for your specific soil type and forage species. 

The following table reports yield response of several forage types to various fertilizer application rates across a number of soil zones and locations in Saskatchewan. Note the synergistic effect of applying more than one nutrient (nitrogen and phosphorous) with a two to three-fold increased yield response as compared to applying nitrogen alone.

Click to enlarge

When soil testing to determine forage fertility requirements, evaluation of soil pH is important as it influences the availability of plant nutrients. When soils are very acidic (pH less than 5.5 to 5.8), soil bacteria and nitrogen-fixing bacteria in legume stands are adversely affected and soil biological activity is reduced⁷. Optimum nutrient uptake by most crops occurs at soil pH between 6.0 and 7.0.

In some regions across Canada, acidic soils are a limiting factor for forage production. To make soils less acidic, a common practice is to apply a material that contains some form of lime. When an application of lime is needed, the lime should be incorporated at seeding or at least six months in advance when overseeding or sod-seeding. With this type of soil remediation, pH is improved, and less fertilizer will be required due to better availability of soil nutrients. As with all soil factors, soil testing is essential to determine whether the pH needs adjusting and the best and most cost-effective management practices to employ.

As with all rejuvenation treatments, costs and benefits of fertilization need to be carefully evaluated. The goal of fertilizing is to decrease the per unit cost of producing forage. However, higher yields do not necessarily translate into lower costs or increased profits due to fertilizer and application costs. Optimal fertilizer costs are affected by hay prices, fertilizer prices and the base land cost. As hay prices increase the willingness to pay for fertilizer should increase. As land costs increase the willingness to pay for fertilizer should increase. Therefore, it is important for producers to know their cost of production (COP) and adjust their strategy based on the current price situation.

The BCRC webpage, Improving Forage Yields, provides more detailed information about fertility and forage stands. To learn more about the economics and economic impacts of fertilization see the factsheet Historical Review of Forage Fertilization Research.

Mechanical Disturbance

Mechanical disturbance can be done using cultivator or anhydrous shanks, knives, or rotary harrows. Whatever type of equipment is used, the objective is to disturb 30 to 50 percent of the perennial forage stand to a depth of two to four inches using one or two passes in the early spring prior to plant growth. This will create a rough surface so the need to level the area using a drag or land roller after disturbance is likely.  

This form of rejuvenation increases the decomposition of root material, releasing nutrients into the soil and making them available for plant use. With sufficient precipitation, the release of nitrogen will result in increased forage growth similar to applying fertilizer.

Although thinning of the stand and reduced forage production is seen initially, this method of rejuvenation may result in a longer-term increase in forage yield. However, disturbance of weed seeds can result in weed problems. It is important to note that using mechanical disturbance to improve forage production is very dependent on adequate moisture conditions.

Work at the Western Beef Development Centre at Lanigan, SK showed a 145% yield increase on crested wheatgrass pastures when a stand was spiked (minimal disturbance) in mid-April with a ¾ inch knife as compared to no disturbance⁸. When including nitrogen fertilizer along with the spiking treatment, there was a 202% yield increase with 50 lb N/acre and a 289% increase with the addition of 100 lb N/acre. In this study, treatments were very timely with spring rainfall contributing to positive growth response.

Studies conducted at five sites in central Alberta using an Aer-Way aerator for mechanical disturbance showed no significant yield response⁹.

Herbicide Application

Selective herbicides can be used to control unwanted plants (woody re-growth, brush expansion, poisonous and invasive plants) that are competing with desirable forage species.

Registered products are not available to control all species and some treatments may be expensive and difficult to apply. Several treatments of follow-up may be required for effective control and there is sometimes a risk of damaging or eliminating some desirable plants.

Herbicides can be applied using a regular ground sprayer where ground conditions allow. Wick applicators are effective for controlling weeds that are taller than the forage stand and can minimize the amount of herbicide applied which can be a cost saving measure.

A number of herbicides are registered for weed control in forage crops. Contact a regional agrologist for more information and specific recommendations for usage and application.

Mowing

Mowing can be used to remove unwanted vegetation such as weeds or brush. The removal of these plants can provide a competitive advantage to the more desirable forage species, allowing them to make use of nutrients, sunlight and moisture and potentially outcompete the less desirable plants.

This method of rejuvenation is very hard on equipment when used on rough terrain and can be expensive and time consuming. Initially there is a reduction of the available forage but longer-term improvements in yield may be achieved. In the case of trees and shrubs, re-mowing is required as suckering and increased woody branches will occur. Mowing two years in a row is much more effective for woody plant control than only one mowing followed by another mowing several years later. Following mowing, cattle will browse new suckers of most woody species if stock density is high enough to reduce selective grazing.

Sod Seeding

Sod seeding is the direct seeding of forages into an existing perennial forage stand in order to improve species composition without breaking up the sod. In these situations, desired plant species densities have become too low and undesirable or invasive species too numerous in the stand. The use of a non-selective herbicide, such as glyphosate, is used to suppress existing and actively growing vegetation in order to allow for successful establishment of new seedlings. If not suppressed, the competition from the established plants, for both nutrients and soil moisture, will greatly reduce establishment of the new forage seedlings.

As with all rejuvenation options, the success of sod seeding is largely dependent upon adequate soil moisture to allow new seedlings to establish. Advantages of direct seeding into sod include not exposing the land to erosion as may occur with breaking and reseeding, plus conservation of available soil moisture that does exist. Additionally, soil fertility is important for any forage establishment method so soil testing and fertilizing as required are necessary.

The use of zero-till seeding equipment is common when seeding annual crops but can also be used for sod seeding forages. The proper equipment will provide good soil penetration, seed-to-soil contact, and coverage on most soils, all of which are important variables in seedling establishment.

A project conducted by the Western Beef Development Centre (WBDC) compared different zero-till seed openers to sod seed alfalfa into grass stands. All of the openers tested worked well in this situation with similar alfalfa seedling establishment results when comparing treatments. More details on the results and use of zero-till openers is available in the WBDC factsheet, A Comparison of Zero-Till Seed Openers for Sod-Seeding Alfalfa for Pasture Rejuvenation and in the following video produced by the WBDC.

As the purpose of rejuvenation is improvement of forage quality and yield, the use of a legume is usually recommended. Alfalfa tends to be the easiest to establish, seedlings are vigorous, plants grow quickly, and the crop is quite adaptable to a range of soil and moisture conditions¹⁰. Legumes including birdsfoot trefoil, sainfoin, and cicer milkvetch are slower to establish than alfalfa but provide a non-bloating, grazing tolerant forage source. Tame grasses are more difficult to establish when sod seeding into a stand where grasses are already present.

A study of sod-seeded alfalfa and sod suppression at sites in Manitoba showed a dramatic difference in forage production between sprayed and non-sprayed areas, as suppressing the existing forage plants allowed alfalfa seedlings to take full advantage of available moisture¹¹. At a second Manitoba location, sod suppression more than doubled forage production with newly established alfalfa as compared to non-sprayed sites.

In a semi-arid environment (Swift Current, SK), sod seeding alfalfa into grass stands that had strips sprayed out with a herbicide provided the most favourable results when considering forage production over three years following the treatment. Average daily gain for animals grazing the rejuvenated stand also showed the best results when sod seeding occurred as compared to fertilizer, spiking, or cultivated treatments. In a relatively dry location with lighter soils, this method allowed for maintenance of soil cover while still reducing the competition from established plants. As compared to cultivating and breaking a forage stand, the killed sod helped to retain moisture for new seedlings being established. Additionally, because strips were sprayed out rather than the entire stand, not all forage was taken out of production as is the case with breaking and reseeding.

At the same semi-arid prairie location, the effect of width of sprayed-out strips was also evaluated. Results showed a 50-centimetre width with seed placed directly in the centre of the strip as having the best establishment and dry matter production three years after the treatment. Production of the existing and adjacent crested wheatgrass and newly seeded alfalfa was good while weeds were minimized.

Intentional overgrazing to suppress plants and reduce competition has been used but is less successful than herbicide. If using extreme grazing pressure in the season prior to sod seeding, careful management must occur to avoid eliminating desirable species. Research at Lacombe, Alberta found that intensive grazing the year before sod seeding alfalfa or cicer milkvetch into a bluegrass dominated pasture was not enough to sufficiently reduce competition¹². However, on bromegrass dominated sites this technique was more successful. A study in Quebec using sheep to graze a smooth bromegrass/reed canarygrass pasture both prior to sod seeding red or white clover and in the two months following seeding, resulted in similar densities of clover as compared to a 2.9L/acre application of glyphosate two weeks before seeding. However, longer term competition from the existing stand was better controlled by glyphosate than grazing and as a result clover yields and quality tended to be higher when glyphosate was used for suppression as compared to grazing¹³.

The BCRC webinar, Practical Applications of Forage Rejuvenation, provides an overview of a number of rejuvenation options with a focus on successes observed using sod seeding on relatively dry sites at Swift Current, Saskatchewan (32:50).

For a more in-depth look at sod seeding options, including suppression, seeding logistics and types of equipment, refer to the publication by the Manitoba Forage & Grassland Association and their partners, “Sod Seeding: Seeding forages into existing stands using minimal tillage”.  

Overseeding of Legumes

The objective of introducing a legume into an existing low plant density forage stand can be achieved by broadcasting seed followed by a harrow, roller, and/or graze to encourage seed-to-soil contact and incorporation of the seed into the sod to increase germination success.

The success of overseeding is largely dependent upon reduced competition from already established plants. For this reason, fertilizing when overseeding is not recommended as added nutrients will also be used by plants already in the stand, increasing the competition for new seedlings.

Overseeding is a relatively inexpensive rejuvenation technique however, establishment success is highly dependent upon favourable conditions. Low density stands will have a much better chance for establishment success as compared to stands where established forage is already quite dense. Adequate moisture is also critical for legume establishment when overseeding.

Frost seeding is a technique that has been used successfully mainly in parts of Eastern Canada to introduce primarily legumes into an existing forage stand in areas where the terrain or stones limit use of large seeding equipment¹⁴. Forage seed is broadcast in the winter on top of snow or early spring when frost is still occurring. The effect of the snow melt helps carry the seed down to the soil surface and alternate freezing and thawing of the ground heaves the surface allowing the seed to be incorporated into the soil. Legumes are more successful with this seeding method as they tend to be denser than grass seed and they germinate at lower temperatures which allows for growth to occur early in the spring¹⁵. Establishing grasses with frost seeding is much less successful as they are less dense and tend to remain on top of the soil delaying growth until warmer temperatures arrive which often coincides with drier weather. The cost of equipment is low, but seedling mortality is high resulting in higher risk for establishment success. Similar to other rejuvenation techniques, adequate moisture is very important for frost seeding to result in forage establishment.

Some producers have successfully used livestock as a low-cost way to introduce new legume plants into a pasture stand. If livestock are fed legume seeds by adding to a grain or mineral mix some “hard” seeds will remain viable as they pass through the digestive tract. The seeds pass through the animal but will not germinate in freshly excreted manure. As the manure breaks down and becomes distributed on the soil some intact seeds may germinate. Seeds need to be raw and undamaged, untreated and with no mechanical injury or scarification from harvest. The successful of this method is variable and produces a very non-uniform stand as random seedlings do establish.

Whether sod seeding or overseeding legumes into an existing forage stand, the following benefits can be achieved if establishment is successful:

• eliminating the need for nitrogen fertilization as the legume will fix nitrogen and provide for requirements of grass plants within the stand
• increased forage quality with higher protein content which results in improved grazing animal performance
• seasonal distribution of forage growth through the growing season as legumes are more productive during mid-summer as compared to cool-season grasses.

Producers discuss their experiences and the value of including legumes in pastures, whether when establishing a new stand or through rejuvenation, in the following video from Alberta Agriculture and Forestry.

Break and Reseed

The most traditional yet drastic approach to rejuvenation has been to terminate the existing stand using a non-selective herbicide such as glyphosate, followed by tillage and reseeding. This method requires a longer-term time commitment and is typically used when undesirable plants such as invasive or woody species have encroached upon a pasture and the density of desirable plants is quite low. Often an annual cereal crop such as oats or barley is grown during the first year followed by the establishment of forage species in the second year.

A significant drawback to breaking and reseeding an established stand is the loss of production in the initial year. If moisture conditions are not favorable, it can take more than one year to re-establish the forage stand. Other challenges include the potential for erosion and loss of soil moisture when tillage and establishment of the new stand occurs. The costs of re-establishing a stand are significant as field operations include tillage, seedbed preparation and seeding. One must also consider access to the right equipment. 

Advantages to this method of rejuvenation include the potential release of soil nutrients for use by the following crop. If the objective is a complete change to the forage stand including removal of undesirable species or a shift from one forage type to another (grass to legume or grass-legume mix) then breaking and reseeding may be the most viable option.

With any method of seeding forages, proper seedbed preparation is important. A firm seedbed prior to seeding allows for better control of seeding depth and seed-to-soil contact. A good rule of thumb for firmness is that a boot print in the soil should not be more than a ¼ inch (6mm) deep. Loose soil can result in excessive seeding depths.

The Forage Establishment page provides more information specific to reseeding of forage species if this rejuvenation technique is used.

A detailed overview of the important steps in establishing a high-legume pasture is presented in the following video developed by Alberta Agriculture and Forestry.

Evaluating Costs and Benefits of Rejuvenation Options

The estimated cost to rejuvenate a forage stand is relatively simple to calculate using published average custom and equipment rental rates plus price of inputs (i.e., herbicide, fertilizer, seed). Benefits are more difficult to predict as yield responses may be quite variable. However, estimates can be used to determine potential increases in productivity.

A study conducted at two sites in Alberta tested a variety of methods and evaluated the economics of rejuvenating the productivity of low producing forage stands. The factsheet, Best Methods for Pasture Rejuvenation, prepared by Alberta Beef Producers and the Alberta Beef, Forage & Grazing Centre, provides an excellent summary of what they learned including challenges when trying to rejuvenate pastures in a low moisture situation.