Soil Sense
Imagining Garden

Soil is a main factor that provide an anchor for the plant's roots provides nutrients and water, and act as a reservoir for the oxygen that plant roots need to live and grow. Soil is the collection of natural bodies on the Earth’s surface that contains living matter and is capable of supporting plants. The nature of a soil depends upon the combination and interaction of five factors-climate, plant and animal life, parent material, topography, and time.


Soils have a different kind depend on different regions because they are made up of weathered rock and minerals. Different kinds of rocks, and different ways that weathering affects different types of rock result in different of soils. "For example, soil that is derived from granite tends to be acidic. Because granite is a hard material, the soil particles might be relatively large, especially when compared to soils derived from limestone, which are also more alkaline. The material from which soils originate affect the kinds of plants that grow well, the frequency of irrigation, need for more or less plant food, and need to adjust the soil's pH."


The weather of each region is also affecting on soils. In the warm and wet area, soils are wet because they receive additional water from higher places on the landscape by surface or subsurface flow. In addition, many of the minerals that act as plant nutrients are washed away. The soil becomes more acidic and contains a large percentage of iron. You need additional fertilization to produce healthy plants in red or yellow soils.


In arid environments the soils are often low in nutrients. In these environments, the soils need to wash with a large amount of water to remove excess salts before plants can be grown successfully, and periodically after that to prevent building up of salts. Soils in dry climates tend to be on the alkaline side. 

Organic Matter

Organic matter is a collective term, assigned to the realm of all of this broken down organic matter. Basic structures are created from cellulose, tannin, cutin, and lignin, along with other various proteins, lipids, and sugars. It is very important in the movement of nutrients in the environment and plays a role in water retention on the surface of the planet. The organic matter in soil derives from plants and animals. In a forest, for example, leaf litter and woody material falls to the forest floor. A teaspoon of healthy soil contains an entire universe of microorganisms. Yeasts, bacteria, and fungi are invisible but vitally important to soil health because they help decompose organic matter. When it decays to the point in which it is no longer recognizable it is called soil organic matter. When the organic matter has broken down into a stable substance that resist further decomposition it is called humus. Thus, soil organic matter comprises all of the organic matter in the soil exclusive of the material that has not decayed. One of the advantages of humus is that it is able to withhold water and nutrients. Therefore, giving plants the capacity for growth. Another advantage of humus is that it helps the soil to stick together which allows nematodes, or microscopic bacteria, to easily decay the nutrients in the soil.


One source of groundwater is soil organic matter and sedimentary organic matter. The major method of movement into the soil is from groundwater. The amount of rainfall is an in direct proportion of organic matter in soil. The regions that have rain regular and abundant, organic matter content averages 5 to 6 percent or higher up to 10 percent. In the regions with little of rain, organic matter can be as little as a fraction of a percent. Organic matter improves workability or structure of clay soils. As fine soil particles bind with micro-organisms, clay particles become stable clumps, or aggregates. Thus, instead of forming a tight mass that sheds water, soil has space between aggregates for water and air to penetrate. In a similar way, organic matter also improves sandy soil, helping it to better retain water and fertility.


Water and Air

Pore space is the space in soil, this space contains the liquid and gas phases. It contributes a major role in infiltration rates in many soils as well as preferential flow patterns, hydraulic conductivity and evapotranspiration. In your garden, these spaces are essential for air, water, and roots to move through the soil and for microbes to survive. All of these resources are necessary for roots to perform their life functions. Both the mineral and organic portions of soil influence the amount of pore space the soil contains. The healthy soil is depending on the mineral particles, because large the mineral particles generate more pore space in soil and pores let water flow through, while small pores hold water for plants to use as they need it.



Soil Types

Soil type usually refers to the different sizes of mineral particles in a particular sample. Soil is made up in part of finely ground rock particles, grouped according to size as sand, silt and clay. Each size plays a significantly different role. Most soils are a combination of two or more of these types.


* Sand: Sand is a naturally occurring granular material composed of finely divided rock and mineral particles. Soils primarily made up of sand called sandy soil and have the largest particles and the largest amount of pore space. Sandy soils drain quickly, so gardener can work soon after rain or irrigation. The sandy soil warms faster in spring than clay soil that allowing gardener to grow their vegetable and annual flower in the ground and off to an early start. Sandy soils drain quickly, so it cannot supply plants with enough moisture for optimum growth. As water passes through sandy soils, it takes nutrients with it, which is the reason sandy soils are usually low in fertility.


* Silt: Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in a surface water body. It may also exist as soil deposited at the bottom of a water body. Silt is nearly microscopic soil particles. Silt is smaller pore spaces than sand, so it will drain more slowly than a sandy soil and retain more nutrients.


* Clay: Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Clay minerals are typically formed over long periods of time by the gradual chemical weathering of rocks, usually silicate-bearing, by low concentrations of carbonic acid and other diluted solvents. These solvents, usually acidic, migrate through the weathering rock after leaching through upper weathered layers. Individual clay particles are microscopic, so its pore space is very small. The pore space of the clay is small, so it holds more nutrients than other soils. Because the pore space of the clay is small, it makes the roots difficult to work their way through the soil. The garden with high percent of clay in soil may be difficult for growing. Adding organic matter will allow the soil to form aggregates, making the soil easier to work.



Soil Texture

Soil texture is a qualitative classification tool used in both the field and laboratory to determine classes for agricultural soils based on their physical texture. The classes are distinguished in the field by the textural feel which can be further clarified by separating the relative proportions of sand, silt and clay. Soils are almost always a mixture of sand, silt, and clay. Soil textures are classified by the fractions of each soil separate (sand, silt, and clay) present in a soil. The ideal is a loamy soil, which scientists classify as consisting of 40 percent sand, 40 percent silt, and 20 percent clay. Loam is ideal because it retains moisture and is fertile, yet has a favorable quantity of pore space for air, water, and roots.


* Determining the soil's texture in your garden: You can determine soil texture by place approximately one tablespoon of soil in palm. Add water a drop at a time and knead the soil to break down all aggregates. Soil is at the proper consistency when plastic and mobile, like moist putty.


Click here to see detail of determining the soil's texture. Modified from: Thien, Steven J., Kansas state University, 1979 Jour. Agronomy education.


Soil Drainage

Water is essential for plant growth. However, either too little or too much water can result in decline and death of plants. For this reason, internal drainage characteristics of soils are possibly the one biggest factor that will determine which types of plants will grow on a particular landscape site. When soils retain too much water, or restrict water movement through them, the result can be root suffocation, root disease, and eventual root death. Drainage is how fast and how much water moves through the soil. Soil with good drainage has a great supply of oxygen, which is vital to root and plant health. On somewhat poorly drained sites plants may not die, but instead show chronic decline symptoms associated with root loss. These symptoms may include yellowing of leaves (chlorosis), defoliation, marginal scorching, dwarfed foliage, and dieback. Trees and shrubs experiencing root decline from excess water are also more susceptible to attack and invasion by secondary diseases and insects. The best way to determine how well your soil drains is to dig a hole about 12 inches deep. Fill the hole with water. Depending on your soil type and existing moisture, the water should drain in a few hours or at least overnight. If water remains in the hole after 8 to 10 hours, you will need to improve the drainage, unless you're willing to limit your plant choices to those that tolerate wet feet. If the drainage in your garden is not well, you can choose plants that can grow in the west soil, or plant in mounds or beds raised higher than the surrounding soil.


Test Soil

Soil conditions may vary from backyard to backyard. For the most efficient and effective use of organic soil amendments, a soil test is advisable, if possible. Even a simple test using a soil test kit can help you to judge what your soil needs for 3 key elements. Soil should be tested periodically throughout the growing season, but it is especially recommended testing before planting in spring and when preparing beds in fall. If you feel your plants are not growing well, a soil test may help. Annual applications of fertilizer can raise the nutrients to excessively high levels, reducing plant growth and prevent seed germination. A soil test can pinpoint nutrient deficiencies and excesses, as well as a guide you toward materials that will help correct problems. Soil tests are a time- and money-saving tool because they point out exactly what amendments are needed, thus eliminating needless plant food applications.


"Getting pH right Chemical amendments are commonly used to modify soil pH. Acid soils are easier to correct than alkaline ones. Limestone is an effective amendment that raises soil pH. Two types are available: dolomitic limestone, which is high in both calcium magnesium, and calcitic limestone, which is high in calcium. In most cases dolomitic limestone is the best form to use. Where annual rainfall is low, such as throughout much of the western half of the U.S. and especially the Desert Southwest, soils are commonly alkaline, not acid. Amendments to acidify soil include iron sulfate and elemental sulfur. Use iron sulfate when the pH is only slightly high, applying 5 to 10 pounds per 1,000 square feet. But if the pH is 7.5 or higher, use elemental sulfur to lower it. Do not over apply. Excessive amounts of sulfur can damage plants. Extremely high-pH soils and soils formed from limestone are almost impossible to acidify to a level where acid-loving plants will grow well. Gypsum is sometimes recommended to improve drainage in heavy soils. However, gypsum is effective for this purpose only when the soil contains excess sodium. Use gypsum when soil test recommendations indicate a need for it."


Organic Soil Amendments

Healthy soils grow healthy plants. Healthy soils require organic matter, like compost, microbes, and moisture to support an environment that suppresses diseases and helps plants absorb nutrients. The result is strong plants and healthier flowers and higher quality fruits and vegetables that naturally resist diseases and pest. In both clay and sandy soil, organic matter contributes to a healthy soil system. Compost is one of the best organic soil amendments, while compost can bagged or in bulk, or you can make it by yourself. Following is descriptions of some of the best organic soil amendments to use.


"* Manures Years ago, suburban neighborhoods often smelled like steer manure as thousands of homeowners spread it on their gardens in springtime. Manure, which can be high in salts, is an inexpensive source of nitrogen and it can increase microorganism activity. If mixed into soil annually, manure will gradually improve soil structure as it decomposes. Use only aged manure near growing plants or prior to planting; fresh manure can burn plants but is fine to apply in the fall or whenever it will have time to partially break down before plant roots reach it. Poultry manure is also used as an amendment, sometimes combined with steer manure. Specialty manures, such as bat guano and worm castings, are effective. Because worm castings and specialty manures are usually expensive, you may decide to reserve them for your most prized plants. Processed sewage sludge is a popular amendment. It contains nitrogen and can also be used as a soil amendment."


"* Wood products The most prevalent commercial organic amendments for soil are wood products, such as ground bark and composted wood chips. These organic amendments are sold in bags and in bulk. They are especially good for opening up heavy soil. Wood products work well as long as they are thoroughly composted. Wood byproducts such as sawdust and shavings that are not composted can consume the nitrogen in the soil to the detriment of plants. If you use them, add some nitrogen plant food at the same time. Sometimes suppliers combine manures and wood products. Again, be sure that these are thoroughly composted. A reputable supplier should be able to provide you with certification and proof that the compost you purchase is not contaminated with excessive weed seeds or weed control products."

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