Improving Survival of Sod-Seeded Alfalfa

Establishment success and production of sod-seeded alfalfa can be greatly improved by killing off the existing sod with herbicide before seeding, then applying fertilizer with the seed.

Although seeding alfalfa directly into existing grassland is not a new method of pasture renovation, the practice has not been widely adopted because the success rate has not always been high. For that reason, traditional methods of renovating pasture have been favoured over direct seeding.

Table of Contents

• Disadvantages of Conventional Renovation
• Direct Seeding Has Advantages
• Four Steps to Improved Survival
• Sod Suppression is the Key
• Things You Should Know
• Results From the Study of Sod-Seeded Alfalfa and Sod Suppression

Disadvantages of Conventional Renovation

The conventional method of pasture renovation usually involves a number of tillage passes before reseeding. However, there are distinct disadvantages to this tradition:

• The operation is expensive and time consuming.
• Grazing is severely limited, if not curtailed entirely, during the renovation period.
• Much of Manitoba's pastureland is stony, saline, on rugged topography, subject to erosion or a combination of all these.
• Cultivation may be difficult on steep land and exposes the land to wind and water erosion. Stones and rugged terrain are hard on machinery.
• Tillage dries out the soil. This is particularly critical on dry, coarse-textured soils.
• A "good catch" is still not guaranteed. In fact, seeding into dry topsoil created by successive tillage passes is often a problem.

Direct Seeding Has Advantages

Direct seeding into existing sod is an alternate method of renovating pastureland. The advantages over conventional methods are many:

• Direct seeding does not expose land to erosion.
• One pass sod-seeding is less expensive than conventional methods of pasture renovation.
• Rocks are not disturbed and pulled to the surface; wear and tear on equipment is held to a minimum.
• Soil moisture is conserved.
• Access to rough terrain is easier than with traditional methods.
• Delays in seeding because of unfavourable weather or site conditions are held to a minimum.

It's a Fact

There are approximately 3,575,000 acres of native and 800,000 acres of tame pastureland in Manitoba for a combined total of more than four million acres. Total value of production from these lands in 1991 exceeded $300 million. Approximately 13,000 producers use forages in their cropping systems.

Four Steps to Improved Survival

A recent study by the University of Manitoba's Plant Science Department has examined the effect of chemical burnoff of existing sod and application of fertilizer at seeding on the survival of sod-seeded alfalfa. As a result of the study, several suggestions for improving the survival of sod-seeded alfalfa may be made.

1. Spray existing sod with 1 L/ac (2.5 L/ha) of glyphosate (Roundup) prior to seeding. Burnoff can begin in the spring once existing foliage is growing vigorously and the threat of a killing frost has passed.
2. Inoculate all seed with a viable rhizobia prior to seeding. Always use registered forage seed. Refer to Seed Manitoba for recommended varieties.
3. Use a zero tillage drill or a specialized forage drill to ensure good seed-to-soil contact.
4. Soil test prior to seeding to determine fertility requirements, then apply fertilizer as required.

Sod Suppression is the Key

Studies conducted by the University of Manitoba's Plant Science Department have shown that sod suppression and fertilizer use can improve seedling emergence and survival and dry matter production of sod-seeded alfalfa. The studies were conducted on two sites, near Gladstone and Portage la Prairie.

Things You Should Know

• The number of alfalfa plants to emerge and survive can be significantly increased by removing the competition of existing vegetation through non-selective chemical burnoff before seeding. Dry matter production of alfalfa on burned-off sod can be increased several times over non-treated land.
• Sod-suppressed sites may exhibit increased dry matter production during the year following establishment, as well as in the establishment year.
• Soil moisture has a great bearing on the success of sod-seeded alfalfa. The drier the site, the more important it is to remove the competition of the existing grasses. Direct seeding helps to conserve whatever moisture there is.
• Soil fertility also has a direct bearing on the rate of success of forage establishment. Always soil test your pasture acreage for nutrients, as well as your crop land. Fertilize as required.
• On the sites used for this study, applying 26.7 or 35.6 lb/ac (30 or 40 kg/ha) of phosphorous (P₂O₅) with the seed improved plant emergence and vigour and increased dry matter production significantly over non-fertilized planting. However, applying 35.6 lb/ac (40 kg/ha) of phosphorous did not increase emergence or dry matter production significantly over 26.7 lb/ac (30 kg/ha).

Results From the Study of Sod-Seeded Alfalfa and Sod Suppression

Table One: Dry Matter Production at Gladstone Site (in kg/ha)

Table Two: Dry Matter Production at Portage la Prairie (in kg/ha)

Table Three: Dry Matter Production in Year Following Establishment (in kg/ha)