Richard Taylor, Extension Agronomist; rtaylor@udel.edu
In Part III of this series, I discussed the advantages of planting into moist soil during the ideal planting window for the selected forage species. I then discussed the planting options, such as conventional seedbed preparation and no-till seeding. Along with these options, I discussed the need for calibration of the planter or drill to ensure the use of the proper number of pure live seed (PLS) per acre. Let us assume that the new planting has emerged from the soil so it is time to think about how to properly manage the new seeding to ensure a successful establishment and long-term productivity.
Usually, even before the seed germinates, grazers want to know when they can return animals to the pasture to graze it. Hay producers have an easier time deciding when to begin using a new field, especially for fall planted fields since cool-season grasses will signal their successful establishment by flowering in late spring or early summer the year following seeding.
For new pastures, the key to long-term health of the pasture is to wait about 12 to 18 months before grazing a new field. This means that the new pasture will need to be hayed at least once and possibly several times in the year following fall seeding. From a practical viewpoint, few grazers will wait 12+ months since it means not grazing the field until the second spring following fall seeding. At a minimum, a new fall-seeded pasture should be hayed in late spring or early summer the year following seeding and then allowed to regrow to a height of 8 to 12 inches before grazing is begun. It is possible to plant in the fall and begin grazing first thing the following spring but you will be sacrificing stand health and longevity with this practice.
Nutrient management plans call for a new soil test once every three years but a yearly sample will help the grazer manage the pasture better. This is very important if nitrogen (N) fertilizer inputs are used to stimulate the productivity of a pasture. Even without N fertilizer applications, the natural deposition of urine and feces in a pasture creates small areas where the process of nitrification produces acidity that can significantly lower soil pH in the small area. Higher stocking rates and intensive pasture rotations will result in more uniform spreading of the urine and feces (especially for ruminant animals); and therefore, a greater proportion of the pasture will be impacted by lower pH (more acid soil conditions). Since it can take a year for lime to move an inch down through the soil, yearly soil testing will allow the grazer to begin neutralizing soil acidity as it is produced by the soil N-cycle.
Another aspect of soil fertility to consider is the use of fall applied N to improve the rooting of pasture plants as well as help stimulate growth the following spring for early grazing. Although the practice has long been used in the turfgrass industry, those of us in forage management are just realizing the potential benefits to pastures of fall N applications. Small amounts of fall N (about 30 lbs N/acre) should be applied in mid-October and mid-November, since at these times topgrowth has ceased but the deep soil layers are still relatively warm. The N stimulates further root growth, creating pasture plants with deeper and larger root systems as they enter the winter period. Some of the N is stored in the plant and available to stimulate topgrowth the following spring as the hours of daylight increase and air temperatures warm. This type of fertilization makes for a stronger plant going into the summer months (greater rooting depth and therefore greater available soil water to draw on) and can improve the competitiveness of the pasture grasses against weeds.
Probably the number one key to maintaining the health and competitiveness of a pasture is to use rotational grazing where plants are allowed to fully recover from the prior grazing period (grow to a height of 8 to 12 inches or more) and the grazing interval is kept short enough that the same plants are not grazed over and over again during a rotation cycle. Generally, this means rotating livestock out of a paddock or grazing cell within three days of moving the animals into the paddock. This time can be stretched to as much as a week but the more rapidly the animals are moved among paddocks in the rotational grazing scheme the healthier the pasture. Another aspect to using rotational grazing is to not put animals on pasture when soil conditions are too wet when the presence of animals can lead to compaction issues. Not grazing when plants are under drought stress is also a key consideration. Use the extra forage produced during the spring and fall to make hay that can support animals on a heavy use pad during periods of wet weather, drought, or other conditions leading to poor pasture growth.
Another method used to maintain healthy and vigorous pastures is to periodically overseed pastures in the fall with grasses and/or legumes. Some producers do this every year while others do it every couple of years. In most cases, the new seedlings must compete against the established plants in the pasture so that there is often limited ‘take’ from the germinating seed. However in the weaker areas of the pasture stand, there will be more light, water, nutrients, and space for the seedlings so establishment will be better in these areas. The weak areas would be where weeds could become established but by overseeding the pastures weed encroachment is limited or prevented.
The species to use for overseeding should be those that can grow rapidly, especially in the cool conditions of late summer and early fall. This would include such species as the ryegrasses, festulolium, ladino white clover, and red clover. Although just broadcasting the seed over the surface and then using a chain harrow or other implement to slightly cover the seed has been used, the best seeding method is to use a no-till drill and drill the seed into the soil. Seeding rates typically used are about one-quarter that of a normal new pasture seeding rate since most of the seed will be planted where established plant competition will not allow the new seedlings to establish successfully.
Finally, the producer can manage the balance of legumes and grasses in the pasture by his/her fertilization practices. Potassium and phosphorus applications along with 1 to 2 lbs of boron per acre per year and maintaining a near neutral soil pH (6.5-7.0) will encourage legume growth. If the percentage of legume is too high and the risk of bloat is too great, N application to encourage grass growth can be used to lower the percentage of legume in a pasture. Grasses, with their fibrous root system are much more competitive for applied N than are the tap-rooted legumes. The available N will stimulate the grass and help it shade the legumes as well as change the proportion of legume to grass biomass.