Seedbed Preparation

May 22, 2007 Print Friendly and PDF

Horse Pasture Improvement - Factors Affecting Seedbed Preparation

There are several factors to consider in seedbed preparation:

Soil Temperature The first requirement for seed germination is a minimal soil temperature. Planting in a cool, wet soil before the soil is warm enough will result in poor germination with many seeds rotting in the soil.

Moisture Seedbed preparation is critical because the seeds are small and cannot germinate if planted too deeply. A seed re requires both moisture (seed softens and swells) and oxygen to germinate. Seedbeds where moisture is not adequate often result in desiccation and death of the new seedlings. The seed should be covered with enough soil to provide moist conditions for germination but not so deep that the shoot cannot reach the surface. Only a small amount of soil is needed to cover the seed and keep it from drying out. Remember, if the seed is buried too deeply, the seedling will never make it to the surface.

Firm Seedbed A firm seedbed is best when establishing forages. The soil must be firmly packed around each seed to permit water to move by capillary action from the soil to the seed. The seedbed may require packing or rolling after the seeding to ensure good seed-to-soil contact. The young seedling also requires good contact with the soil so it can absorb nutrients and moisture. Seedbed for forages should be firm enough that one’s footprints in the soil will not be more than ¼ inch deep. A loose seedbed makes it impossible to control the depth of seeding because the tires and the planter sink into the soil.

Tillage

  • The most common seedbed preparation involves tillage of the soil. Tillage serves several purposes.
  • Eliminate existing vegetation.
  • Turn under surface weed seeds - Tillage helps control weeds before planting and reduces the weed population. Weeds are generally much faster growing than forages, and out-compete the small seedlings during establishment. Tilling under weeds, and burying any weed seeds that are on the soil surface (so they don’t germinate) is one method of reducing the weed population. Herbicides may be used to control weeds, but residual effects of herbicides may be a concern.
  • Loosen soil - Tillage operations such as plowing and discing help loosen the soil.
  • Incorporate fertilizer and lime - Fertilizers (especially P & K) and lime work best when incorporated (by tillage).
  • Provide firm seedbed for seeding - Other tillage operations, such as harrowing and cultipacking, help provide a firm, smooth seedbed which is essential for most planting methods, and helpful when harvesting.

Tillage that leaves some residue on the surface will provide a better environment for developing seedlings than an overworked seedbed with no residue or mulch. Too much surface residue or trash may result in seed placement that is too shallow due to the seeding units riding on top of the residue. Cloddy or trashy seedbeds are usually too rough or uneven for uniform depth control and seed placement. Overworking the soil results in fluffy, powdery seedbeds that dry out quickly and are too fine, increasing the potential for surface crusting when it rains. Crusting is particularly a problem with small-seeded legumes. Soil granules, or very small clods, can be beneficial to prevent soil crusting. Major problems with conventionally tilled seedbeds are soil moisture loss during tillage and soil erosion potential until the crop is established.

Other forms of seedbed preparation For partial renovations it is often desirable to plant forage seeds into an existing stand. To give the new forage seedlings a chance for establishment, it works best to stunt, or slow-down the existing forage.

  • Close clipping or grazing - Close clipping or grazing is one method that may be used. This involves clipping or grazing closer than normally recommended. This will “set back” the existing forage and give the new seedlings a chance to establish.
  • Burning - Burning the surface residue is another method of reducing the existing forage.
  • Non-selective herbicide - Non-selective herbicides can be ones that either kill the top vegetative matter, but not the roots such as Paraquat (most plants will grow back); or a translocated herbicide (such as Roundup) that kills the whole plant. The herbicide may be sprayed on alternating strips with only the sprayed areas being reseeded.

Generally the above methods require no-till planting, or frost seeding planting methods.

Strip-tillage involves tilling alternating (narrow) strips of land. The tilled strips are then reseeded. This method leaves approximately half of the field in the existing forage, and half with the new forage, providing erosion control and some forage for haying.

Fertility of Soil The fertility of soil should be determined from a representative soil test.

Phosphorus (P) and Potassium (K) are not very mobile in a soil. Therefore, it is best to apply these nutrients when establishing a pasture so they can be incorporated into the soil where they will be closer to the plant roots.

  • P is very critical for root establishment. Available phosphorus should be at least 50ppm.
  • Broadcast P not as effective as banded P (takes 4 times as much P when broadcast).
  • Demand for K by young seedlings is relatively low. It becomes much more important for yield and persistence once stands are established. Exchangeable potassium should be 300 to 400ppm.
  • Nitrogen (N) is mobile. Do not apply too much nitrogen at any one time. If too much nitrogen is applied, nitrogen will be lost due to leaching and volatilization.
  • The addition of N fertilizer is not recommended in partial renovation because it stimulates re-growth of existing grasses and weeds, increasing competition between young seedlings and existing vegetation for water, light, and soil nutrients.

Soil pH pH of Soil can also be determined by a soil test.

  • Lime is used to raise the soil pH when the soil pH is below 6.2. Lime should be added in the establishment phase and incorporated into the soil.
  • The ideal pH for alfalfa and most legumes is 7.2 with values between 6.5 and 7.5 being satisfactory.
  • Grasses do best when soil pH levels are between 5.5 and 7.0.

Seedbed Preparation In many situations (i.e. sloping or other erosion-prone areas) no-till planting of forages into existing sods is the only option. However, pasture plants are most easily established on well-prepared, clean-tilled seedbeds when a choice between seedbed type is possible. The amount of tillage necessary to prepare a good seedbed depends upon what crop was last grown on the site. When converting cropland into pasture, less tillage is needed than if establishing new pastures on soils formerly in brush or native grasses. When tilling pasture sites, consider the erosion potential and minimize erosion in new pastures. On sloped sites you may want to suppress or kill existing forage with herbicides and no-till into the existing dead sod to minimize or prevent soil erosion. Most grass and legume seeds are small, so a firm, moist seedbed is essential in all situations to obtain a good stand. Seedbeds of this type provide good seed-soil contact and conditions favorable for seed germination and plant emergence.

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This work is supported by the USDA National Institute of Food and Agriculture, New Technologies for Ag Extension project.