How To Love Your Lawn

Chapter 3: Soil Types

Bob Brownmud stood out on the bare dirt of his front yard, looked down, and scratched his head.

"I don't know, Scott," he said to his neighbour. "You tell me what kind of soil I have. I wouldn't know good dirt from bad. I guess I'm going to have to pay for soil testing. Is it expensive?"

Scott Greenlawn smiled. "It can be, but since this is an established neighbourhood, the soil has already been tested by the local agricultural agent. I've got a copy of the report. It'll make choosing grasses and fertilizers a lot easier."

The main reason why people grow a lawn is not to have grass that looks nice, although that has become an end in itself. The real reason people strive to have healthy grass on their lawns is to prevent the erosion of their soil. Erosion of soil is a major contributor to flooding. Here are some photos that tell a tale about soil erosion from Dr. Ray Weil, a soil scientist from the University of Maryland, College Park, MD, USA.

Muddy runoff from tilled fields in Ethiopia Sediment-laden river running through Addis Ababa, Ethiopia, many miles downstream from the eroding soils.

Government research farm in central Ethiopian highlands

Soil clods from research farm before placement in water

Soil clods following placement in water

Soil clods after time has elapsed

General

Soils are the foundation of life. They serve as an anchor for plant roots. Plants need live, healthy, balanced soil for productive growth and protection against pests. Areas set aside for lawns usually have one or a combination of soil types, including clay, silt, loam, sandy loam, sand, gravel, and rock. All soils have five major components: organic matter, minerals, water, air, and living organisms. The seldom-discussed living organisms are very important and consist of earthworms, insects, plants, algae, bacteria, fungi, and other microorganisms. Healthy soils need a balance of mineral nutrients, approximately the following percentages:

– Calcium: 65 to 70 percent; 
– Magnesium: 12 to 22 percent; 
– Potassium: 4 to 5 percent 
– Other trace minerals.

The pH of your soil should range between 5.5 and 7.5. If the pH is above or below this range, then grass plants have difficulty absorbing certain essential nutrients they need to thrive, so you'll have to adjust it and perform more maintenance on a regular schedule. Sometimes the pH healthy balance has been negatively affected by the application of harsh synthetic fertilizers and chemicals and the regular removal of dead organic matter. What this can leave a homeowner with is dry, sterile dirt.

In order to know what you're dealing with in terms of soil, you may wish to determine its chemical characteristics by having the soil tested. The tester should be a company that will give you detailed information about your soil's chemical composition as well as organic fertilizer recommendations. Local nurseries or agricultural offices may be able to provide this service.

One of the best soil tests is to dig out a piece of soil measuring 30 cm (11.75 in.) by 30 cm (11.75 in.) by 18 cm (7 in.) deep and count the earthworms. If there aren't several earthworms, you will need to aerate the soil and add organic matter. The structure of the soil at depths of 30 cm (11.75 in.) and 60 cm (23.5 in.) is important for drainage and deep root development, but the structure of the top 18 cm (7 in.) is the most important. That's where air, organic microbes, earthworms, and feeder roots are concentrated.

Types of Soil

Sand: Sand is grainy soil that holds little or no compost or humus. It drains very well, and as a result, does not hold water very well. It is also lacking in minerals and micronutrients needed by your plants. Roots of plants can easily grow and expand through sand. We all know that Cactus grows in sandy soil. But, did you know that peanuts prefer sandy soil too?

Clay: This is the second major type of soil. It is largely the opposite of sand. It retains water and does not drain well. Heavy clay soils can act as a pot, holding water for days as rainwater ever so slowly seeps through it. Roots can actually drown, as there is no air in the soil. Roots have a hard time pushing

Helpful Hints Still stumped by soil? Flip open the yellow pages and head to the S section. You should have several local companies who both supply and advise customers about the soil products that will work best with their lawn compositions and growing needs.

through it and tend to ball up.

Loam: This soil contains a mixture of clay, silt, sand, and some organic matter. It retains water well, yet is loose and contains plenty of air pockets for roots to breathe. Best of all, it is rich in minerals and nutrients vital to your plants' growth and development.

Humus: Soil containing a rich mixture of decomposed plant or animal matter. It is rich in minerals and nutrients vital to your plants' growth and development.

All soils are composed of a mixture of clay, silt, and sand. Your exact soil composition will most likely be described as a mixture of two or more of these components. Soil is a mixture of air, water, and soil particles. For best growth of your grass, this mixture must be the right balance. The texture of your soil is the mix of the three basic soil components:

* Sand: Soils with particle sizes ranging from 2.0 (.01 in.) to .05 mm (.002 in.)

* Silt: Soils with particle sizes ranging from .05 (.002 in.) to .002 mm (.0001 in.)

* Clay: Soils with particles sizes smaller than .002 mm (.0001 in.)

Loam: Loam is the ideal soil mixture, consisting of 40% Sand, 40% Silt, and 20% Clay. A loam soil will seem crumbly in comparison to a clay soil that is very tight. The best soils for grasses are loamy soils with a 40-60% sand component, a 20-30% clay component, and a 20-30% silt component.

Organic Matter: Organic matter is plant and animal residues, soil organisms (microscopic,) and living plant roots. Organic soil also includes humus matter, which is highly decomposed organic material. Good lawn soils should have at least 2% of organic soils. Organic soil matter helps your plants by supplying usable nutrients and nitrates for growth. Organic matter also helps establish a soil with various crumb sizes (composed of 3 types of soil) of 1 to 3 mm (.025 to .10 in.) This is the best soil structure in which air, nutrients, and water can produce healthy grasses.

For lawn purposes, your concern should not be the fertility of the soil, but rather how the makeup of the soil affects its ability to hold water and to allow air to pass through it. You may need to improve sandy soils by adding organic matter (heavy soils) and clays or clay-loams. For a clay soil, you should add organic matter (light soils) and sand or sandy loams.

The organic matter may be materials such as peat, manure, old sawdust, straw, seed hulls, and other materials. You should thoroughly mix the organic matter with your soil to a depth of 12.75-15.25 cm (5-6 in.) Add extra nitrogen if high quantities of organic matter are added so as to replace the nitrogen that is tied up in the decomposing materials in your soil. Fertility can be improved through the addition of fertilizers and lime (use sulfur if the soil is alkaline.)

Using Soil Tests

Soil Tests Reduce Fertilizer Guesswork

Soil tests reduce the guesswork involved in deciding what kind and how much fertilizer to use. Your soil may contain an adequate level of one mineral nutrient and be quite low in another. A test of your soil will enable you to determine the correct amount of each mineral nutrient to apply.

Did You Know? Some experts believe that over 7% of the world’s soil erodes every year … and that the figure is increasing.

Soil tests are done by laboratories at colleges and universities and by private labs. A soil test result will give you the levels of nutrients in your soil and the recommendation for how much fertilizer your plants will need each year. You don't need to test your soil every year — testing every three to five years is adequate.
To get useful results from a soil test, take a soil sample that represents your lawn and provide

information about the types of grass you're considering on the form provided by the soil test lab. When collecting a soil sample, take samples from a depth of 15.25-20.25 cm (6-8 in.) from at least ten spots in your yard. Avoid sampling areas that are not typical of your yard. Mix the samples together well and take a sub-sample to send to the lab.

If only one or two fertilizer nutrients are needed, you may prefer to purchase fertilizers containing only the needed minerals and apply them separately. Some common fertilizer sources are:

Common Fertilizer Sources

ammonium nitrate	33-0-0-0-0	33 % Nitrogen
ammonium sulfate	21-0-0	21 % Nitrogen
bloodmeal (organic)	16-0-0	16 % Nitrogen
sulfer-coated urea (slow release)	36-0-0	36 % Nitrogen
treble superphosphate	0-45-0	45 % Phosphate
bonemeal (organic)	4-17-0	17 % Phosphate
muriate of potash	0-0-60	60 % Potash
woodashes (organic)	0-0-?	6 % Potash

Soil amendments adjust the pH (soil acidity or alkalinity level) and supply calcium (Ca) and magnesium (Mg) to the soil. Most lawns grow best in moderately acidic soil. Soils with a pH from 5.5-7.0 do not need soil amendments to adjust the pH level.

Lime is calcium carbonate. It will raise soil pH (reduce acidity) and supply calcium. Dolomite lime is calcium-magnesium carbonate. It will supply both calcium and magnesium to the soil and raise soil pH. Sulfur is used to lower soil pH. Apply soil amendments based on the recommendations from a soil test.

The recommended quantities of lime or dolomite should supply enough calcium or magnesium to last several years.

Gypsum Seldom Improves Soil Structure

Gypsum (calcium sulfate) has been promoted as a soil amendment to improve soil structure. In the vast majority of cases, it will not work. Gypsum only improves structure when the problem results from excessive sodium in the soil, which is a rare condition.

Apply lime and other soil amendments in the fall. With vegetable gardens and flowerbeds, till the lime into the soil. On lawns and perennial plantings, fall application allows the winter rains to dissolve and carry the amendments into the soil. Do not apply lime and fertilizer at the same time. Lime, if needed, should be applied at least 30 days before any fertilizer application.

Salinity

Salinity Test Shows Soluble Salts in Soil

The salinity test measures the total soluble salts in the soil. In arid regions, the total amount of soluble salts can accumulate to problematic levels. The following table shows how to interpret a salinity test.

Salt in millimhos per centimeter (mmhos/cm)

4 or above

Severe accumulation of total salts in the soil that may restrict growth of many ornamental plants. Salt level should be reduced by leaching.

2-4

Moderate accumulation of salts. Will not restrict the growth of ornamental plants, but may require more frequent irrigation to prevent wilting.

2 or less

Low salt accumulation. Well below the tolerance of all ornamental plants.

Leaching is the practice of applying irrigation water in excess of the water-holding capacity of the soil.

This excess water must drain downward through the soil, and in so doing, carries the excess soluble salts with it. Three inches of excess water will remove about 50 percent of the soluble salts from the soil. Five inches of excess water will remove approximately 90 percent. When leaching, apply water at a rate that does not exceed the permeability of the subsoil.

Seasons And Soil

Soil Management Practices by Season

Spring:

Cut grass once a week.

Add fertilizers as needed.

Prepare flowerbeds planting.

Cultivate shallowly to control weeds.

Irrigate as needed.

Summer:

Irrigate as needed.

Mulch flowerbeds to conserve moisture and control weeds.

Use shallow cultivation as needed to control weeds. Build compost pile (if desired) with organic refuse (grass clippings, weeds, vegetable trimmings, etc.)

Fall:

Add soil amendments if needed.

Winter:

Add fertilizer to soil if runoff is not a problem.

Go To How To Love Your Lawn Chapter 4: Seeding or Sodding
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