Your Teacher Has Chosen Sources That Match Current Accepted Scientific Facts

This packet contains articles that can be used to form a brief background report for your experiment report.

Your teacher has chosen sources that match current accepted scientific facts.

Topics:

Seed germination process

Needs of plant cells

Needs of grass

If you need more information, you are encouraged to find more information in the library after class.

You are expected to read all of these articles and choose the information that best matches the topic of your experiment.

DO NOT PLAGARIZE!

You will need to use only the most concise information that helps guide your experiment.

Source

(Washington state univserity)

Seed Germination

Late winter is the time of the year to dig out those old seed packets and see if the seed is still good. You may use up a whole packet of beans, carrots or lettuce in one year, but usually there are enough seeds of tomatoes, cucumbers, squash and peppers to last for several years. Just because you have seed left, however, doesn't mean that it is good seed.

Before I launch into a description of how to test the seed, let's talk about seeds a bit. We have all planted seeds, but how much do you really know about them? Learning more about seeds can help improve your success with them.

When you look at a seed you are looking at the seed coat. As people wear coats for protection from foul weather, seed coats perform much the same function. They provide protection against entry of parasites, against mechanical injury and, in some seeds, against unfavorably high or low temperatures.

Inside the seed coat is the embryo, an immature plant with all the parts of the adult plant. A close look shows leaves and a root -- they may be tiny but they are the beginnings of a plant. The seed's embryo leaves are called the "cotyledons." The seed is filled with "endosperm," food that will nourish the embryo during its early stages of development.

Germination is a fascinating process. Seeing a tiny seedling emerge from a dry, wrinkled seed and watching its growth and transformation, is observing the mystery of life unfolding. The first sign of germination is the absorption of water -- lots of water. This activates an enzyme, respiration increases and plant cells are duplicated. Soon the embryo becomes too large, the seed coat bursts open and the growing plant emerges. The tip of the root is the first thing to emerge and it's first for good reason. It will anchor the seed in place, and allow the embryo to absorb water and nutrients from the surrounding soil.

Some seeds need special treatment or conditions of light, temperature, moisture, etc. to germinate. Seed dormancy is very complex, but it protects that living plant material until conditions are right for it to emerge and grow.

Practical lessons can be learned from the seed:

• Seeds with bigger amounts of endosperm can feed the embryo plant longer, while it works its way toward light. Therefore, big seeds can usually be planted deeper.
• Seeds must absorb water to get germination going. Therefore, presoaking seeds may speed up the process.
• Available water is important to the newly emerged root. Therefore, you should plant seeds a little deeper in the middle of summer, when the top of the soil dries out quickly.

You get the picture; so now let's talk about germination testing. Whether left-over seeds will germinate (sprout) and grow depends on how old they are and how they have been stored. With proper storage conditions, the average useful life of some common vegetable seed is much longer than some others.

1-2 years: / 3-4 years: / 5-6 years:
corn
onions and leeks
parsley
parsnips
peppers / asparagus
beans and peas
beets
cabbage family
carrots
eggplant
squash and pumpkins
tomatoes / cucumbers
lettuce
melons
spinach

If you keep your seeds cool and dry, they will last longer, but can you be sure that they are still good? If they are, you can save yourself some money. Before you order your new seed, do a germination test on any seeds more than just one year old. Here's what to do:

1. Put exactly ten seeds on top of a damp, folded paper towel.
2. Put the towel and seeds into a plastic sandwich bag and seal.
3. Label the container with the date and seed variety being tested.
4. Leave at room temperature for a week or so. (Leave parsley, carrot and celery longer; they're slow.)
5. Count the number of seeds that sprout:
6. 10 = 100% or perfect germination
7. 9 = 90% or excellent
8. 8 = 80% or good
9. 6-7 = 60-70% or poor -- sow more thickly
10. 5 or less = 50% or less -- throw the seed out!

By Holly S. Kennell, WSU Extension Agent, KingCounty

Understanding Grass Seed Germination

Source:

Grass seed germination keeps you in suspense! You get one chance, but you wait weeks to see if you did it right!

Are your expectations for the outcome reasonable?

Does every little grass seed sprout and grow?

Many factors affect grass seed germination. The success of your lawn project is not completely under your control, but you can do a lot to improve the final result.

Grass seed germination is simply the growth process that occurs when the seed absorbs sufficient moisture to start sprouting. This is regulated by soil temperature according to the variety of grass. The hull, or hard outer casing, may delay this process until conditions are favorable.

Once germination begins, if the environment changes significantly (like being too hot and dry), the seed or sprout will die. It cannot start to grow, then stop because something is wrong, wait till conditions improve, and then continue the process.

Requirements For Grass Seed Germination

Moisture
Adequate moisture must be present throughout the process. Too little and the seed can dry out. Too much moisture and the seed can rot. Read the article Watering New Grass Seed for guidelines.

Warmth
Soil temperatures should be in the appropriate range for the variety of grass. Cool season grass requires a minimum range of 45 - 55 degrees. Warm season grass requires a minimum 55- 65 degrees. Note that soil temperatures are usually cooler than air temperature. In addition to the density of the ground that is slower to warm up, moisture evaporating from the surface has a cooling effect.

Oxygen
When the sprout breaks through the seed, it requires oxygen for its growth process. The cells are “eating” the food in the seed so they need oxygen just like animals. When soil is over saturated with water, oxygen is not present and the sprout cannot grow. Compacted soil can also contribute to this problem.

Light
A seed has limited resources to support growth while below ground. The sprout must break through the surface in order for the photosynthesis process to function and create food for the plant. Sprouts will not be able to reach the surface if seeds are buried too deep.

Factors that improve grass seed germination

• The seed should be in direct contact with the soil to absorb moisture. Rake the seed lightly after sowing to mix it with the dirt and/or go over it with a light roller to press it into the soil. Get more details at Planting Grass Seed.
• Mulch can help retain moisture. A very thin layer, 1/8” to ¼” is all that is required. Seed covers or compost should be fine screened to avoid clumps that bury the seed. Steer manure is stinky, but inexpensive. Use it only if it is certified weed free. Bedding straw is a good option for large areas, but don’t use hay that has seeds in it.
• Sow grass seed at the ideal time if possible. Cool season grasses will not do as well in higher temperatures. Warm season grasses will not do as well in cooler temperatures. Investigate options at The Best Time To Plant Grass Seed.
• Trouble from above. Birds love to eat uncovered seed. Do whatever it takes to prevent them. Restrict activity of kids and pets that can disrupt the grass seed germination process.
• Wait the appropriate length of time before sowing, when any chemicals like weed killers, fungicides or preemergents have been used on the lawn area. Product labels should indicate the waiting period.
• Consistent, light, frequent watering is essential. Avoid over-watering. Avoid under-watering. See Watering Guidelines.

Typical Grass Seed Germination Time Periods

Grass Type / Number of Days to Germinate
Bentgrass / 10-15
Bermuda / 10-30
Bluegrass / 20-30
Buffalo Grass / 14-28
Centipede / 14-21
Fescues / 7-15
Rye Grass / 5-10

This chart may indicate the amount of time until grass first appears, or until the majority of seed has sprouted. Growing conditions greatly affect this process.

Grass Seed Germination Rates and Storage Effects

The label on a grass seed package provides important information, including the germination rate. A rate of 90-95% is preferred, but some grass varieties will typically be found in the 80% range. The higher, the better. An 85% germination rate means that if you plant 100 seeds, 85 of them should sprout and grow.

Realize that this rating system comes from the supplier doing a test in a laboratory. Your results may vary, usually lower. All the factors discussed above will decrease the grass seed germination rate, as will how long the seed has been stored and in what conditions.

Grass will usually be fine to use for a year after the test date. The germination rate listed should remain valid if the seed was stored in a cool, dry area. Heat will rapidly decrease the seed viability. Moisture may ruin it.

Each year of storage can result in a decrease of the grass seed germination rate by a range of 10 to 25% per year. It can still be used, but the amount applied to an area should be increased proportionately. Because you have to use more seed, don’t automatically assume that older seed being sold at a discount is a good value.

If you have older seed, take a handful and lightly blow across it (outside). Any lightweight seeds that blow away are just chaff, they have died. If a large portion of seeds are dead, start with a fresh batch. If a smaller amount appear bad, or you are unsure, consider planting a test sample. This will delay your project for a couple of weeks, but it might prevent a disappointing venture.

Watch It Grow, Hopefully

Grass seed germination always seems to take a long time, especially when you watch it closely. That makes it very disheartening when the results are less than expected. Sometimes people wait two, three, four weeks, but never see any grass.

The seedmay have failed to germinate. This is unlikely if it is new seed and you followed all the necessary steps. Grass plants can be picked off by pests as soon as they break ground. Birds, snails, slugs, cutworms, pillbugs, earwigs, rabbits, squirrels, rats and mice are all attracted to this fresh salad bar. They can grab it before you see it, or leave such a small percentage that you believe the seed was bad.

Sow a sample crop of seed so you know when to expect the grass plants. Then you can be on the alert for any problems. Plant a number of seeds in a garden pot and keep it in a warm, but protected area. These seeds should germinate a few days prior to most of the lawn area, since the potting soil should be warmer.

This sample will demonstrate the time to expect your lawn grass as well as the germination rate under better conditions. You can also put a few seeds on a wet paper towel stored in a sealed plastic baggie. Watch for signs of sprouting. Then guard the garden!

Source:

What is fertilizer and why do plants need it?

In order for a plant to grow and thrive, it needs a number of different chemical elements. The most important are:

• Carbon, hydrogen and oxygen - Available from air and water and therefore in plentiful supply
• Nitrogen, phosphorus, potassium (a.k.a. potash) - The three macronutrients and the three elements you find in most packaged fertilizers
• Sulfur, calcium, and magnesium - Secondary nutrients
• Boron, cobalt, copper, iron, manganese, molybdenum and zinc - Micronutrients

The most important of these (the ones that are needed in the largest quantity by a plant) are nitrogen, phosphorus and potassium. If you have read the articles How Cells Work and How Food Works, you have heard about things like amino acids, cell membranes and ATP. Nitrogen, phosphorus and potassium are important because they are necessary for these basic building blocks. For example:

• Every amino acid contains nitrogen.
• Every molecule making up every cell's membrane contains phosphorous (the membrane molecules are called phospholipids), and so does every molecule of ATP (the main energy source of all cells).
• Potassium makes up 1 percent to 2 percent of the weight of any plant and, as an ion in cells, is essential to metabolism.

Without nitrogen, phosphorus and potassium, the plant simply cannot grow because it cannot make the pieces it needs. It's like a car factory running out of steel or a road crew running out of asphalt.

If any of the macronutrients are missing or hard to obtain from the soil, this will limit the growth rate for the plant. In nature, the nitrogen, phosphorous and potassium often come from the decay of plants that have died. In the case of nitrogen, the recycling of nitrogen from dead to living plants is often the only source of nitrogen in the soil.

To make plants grow faster, what you need to do is supply the elements that the plants need in readily available forms. That is the goal of fertilizer. Most fertilizers supply just nitrogen, phosphorus and potassium because the other chemicals are needed in much lower quantities and are generally available in most soils. Nitrogen, phosphorus and potassium availability is the big limit to growth.

The numbers on a bag of fertilizer tell you the percentages of available nitrogen, phosphorus and potassium found in the bag. So 12-8-10 fertilizer has 12-percent nitrogen, 8-percent phosphorous and 10-percent potassium. In a 100-pound bag, therefore, 12 pounds is nitrogen, 8 pounds is phosphorous and 10 pounds is potassium. The other 70 pounds is known as ballast and has no value to the plants.

So why don't people need fertilizer to grow? Because we get everything we need from the plants we eat or from the meat of animals that ate plants. Plants are factories that do all of the work to process the basic elements of life and make them available to us.