Seed to Soil Contact is Important
Author: Easy Digging Staff
Bigger, faster crops from firm soil contact
Compressing the soil around your seeds will speed up germination and prevent the young plants from drying out. Image and Info Credit
Seed-to-soil contact is an often overlooked, but important factor in seed germination. At it's core, soil contact is what allows seeds to absorb moisture and begin growing. Weak soil contact delays sprouting by allowing the seeds to remain dormant longer.
Thankfully, there are easy small changes you can make to get good seed-soil contact.
Why is seed-to-soil contact important?
Without proper water transfer, seeds will not begin to germinate. Even after germination, water transfer remains important for seedling health and growth. This is especially important for crops with a low tolerance for drought, like carrots, whose seedlings will die if not kept moist.
"The importance of good seed-soil contact is as basic as it gets," said James Shroyer, professor of agronomy at Kansas State University. "It allows the seed to readily imbibe moisture and initiate germination and eventually emergence. Without good seed-soil contact there are air pockets around the seed and that delays germination resulting in uneven or rather, delayed emergence."
Soil contact gives the seed enough coverage, compaction and moisture to grow. Without it, plants will grow unevenly or be stunted.
Signs of poor seed-to-soil contact:
- Uneven height
- Low germination rate
- Stunted growth
- Small root system
If you have noticed one or more of these problems with your plants, you may have a seed-soil contact problem. Here's how to fix that.
How to optimize seed-soil contact
Seed-soil contact is important because it directly impacts crop health and yields. To optimize your seed-to-soil contact you need to manage both 1) soil moisture and 2) compressing soil around the seeds.
1. Managing soil moisture
Poor seed-soil contact can lead to uneven growth because of varying moisture transfer rates. When some seeds absorb more moisture than others, they may grow faster.
If there is not enough moisture or warmth around a seed, it will not sprout properly. This is because seeds wait for the right conditions to germinate.
Ideally, you should plant seeds in lightly damp soil, and then water the rows immediately after planting. The water should penetrate the soil two inches deep. Proper watering allows soil to settle around the seed to maintain better contact.
Be especially cautious with clay soil as water may penetrate to the proper depth at a much slower rate. Avoid over-watering clay soil by slowly irrigating and giving the soil enough time to properly saturate.
2. Compressing soil around the seeds
A common mistake is to plant into "fluffy" freshly tilled ground. This often leads to uneven seed-soil contact because there are too many large air pockets and open spaces in freshly tilled soil. Seeds may also "fall down" these open spaces and become too deep for proper germination.
It is important to properly prepare the garden bed or row BEFORE planting. The optimal condition is to have loose soil with small air spaces. Being loose makes it easy to open a furrow. And having only small air spaces makes it easy to compress the soil around the seed.
If you aggressively till or turn your soil, you need to ALSO remove the large air spaces before planting. For large spaces, a heavy cultipacker or yard roller can help compress the soil. For smaller spaces, walking over the row or bed provides decent soil compression and air space removal. Don't stomp, just walk. Watering, by rain or irrigation also helps re-compress tiled soil. Remember that you want loose soil with small air spaces.
The first step in planting a row of seeds is to open a furrow of the proper depth. In a small garden, this can be done by dragging the corner of a hoe down the row. While in a farm field, large grain drills and planters have disc openers (coulters) which open a furrow. Then, once the seed has been placed in the furrow, they have a spring-loaded closing or press wheel which compresses the soil over the seed.
A garden seeder works in pretty much the same way, just scaled down. A few garden seeders do have disc openers, but most have a planter "shoe" which is just a long skinny plow with a space between the halves that the seeds are dropped into.
The rear wheel of a garden seeder acts as the closing or press wheel to partly compress soil around the seed. Note that we said "partly compress", this is because garden seeders are light so the only downward force on the rear wheel comes from the operator pushing down on the handles. Fortunately since the operator walks behind the seeder, his footsteps can also help compress the soil. Finally, watering the beds or rows right after seeding will help insure good seed to soil contact.
If you are seeding by hand, by broadcaster, or with a seeder that does not cover the seeds for you, make a plan for how they will get good soil contact. After using a broadcast seeder, either rake the seeds in or apply a layer of soil or compost to lightly bury the seed. Walking over rows and watering (both described above) are the common ways providing good soil to seed contact when planting by hand.
Other dangers to watch out for...
Soil crusting can also hamper seed germination. Crusting is especially common when heavy rainfall is followed by high heat. It prevents germinating seeds from breaking the surface and can inhibit light rain or dew from reaching the seed.
To prevent surface crust, don't over till the soil. On large seeders, don't apply too much pressure to the closing wheels. If you are walking over the row to compact it, walk normally and do not apply excessive pressure (don't bounce or stomp).
You can reduce future crusting by adding organic matter to the soil. Reducing tillage and instead opting for cover crops like tillage radishes will also help in the long-run.
Surface Residue (Hair pinning)
If there is too much plant residue on the soil surface (straw, mulch, grass clippings, etc), seeders with disc openers (coulters) can push the residue down into the furrow and create an effect much like a long bird's nest. Seeds fall into this nest and it holds them away from the soil. If the seeds barely touch the soil, the seed-to-soil contact will be minimal and the seeds will take a long time to germinate. Image and Info Credit
Preventing hair-pinning in the home garden is fairly easy. Using a seeder with a plow style furrow opener (a shoe) works because it pushes the residue aside rather than down into the furrow. You can also temporarily scrape or brush the residue off the row you want to seed. After the seeds are planted and the soil is compressed, you can safely brush the residue back over the top to act as a mulch.
Seed-to-soil contact is vital for healthy plants and a good harvest. Poor contact with soil can result in low yields and poor growth. You can improve germination by paying attention to soil moisture and soil compression. By optimizing these factors your crops will be more successful.
- Sources and Image Credits
- Hair-pinning of Crop Seeds
- Diagnosing poor seed-soil contact in crops
- Requirements for Uniform Germination and Emergence of Corn
- How to Get Strong Germination Outdoors
- Seed-Soil Contact and the role of vapor in germination
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