Soil Conditions

The soil’s main ingredients are (inorganic) minerals, air, water, and (organic) humus, and living organisms. Healthy soils are alive with life forms and their remains. There must be an abundant supply of oxygen available for the organisms. A typical soil supporting rich vegetative growth and serving as a host for insects, worms, and microbes is full of pores. The pore space should be at least 50% with 25% occupied by air and the other 25% occupied by water.

Soils are composed principally of an inorganic fraction consisting of sand, silt, and clay particles. The percentages, by weight, of each of these three components are used to determine the texture of the soil. The organic matter (humus) generally ranges from 2-4% of total weight. Air and water fill gaps between larger particles.

The ability of soil to hold air depends on soil particle size and how well the particles pack and cling together in forming a solid mass. These particle size groups are called “separates” and vary from clays, which are the finest, through silt to sand, to gravel. The particle size of clay is 0.005mm or less. The small particles in a clay deposit can pack so closely together thus eliminating essentially all of the air and water. This virtually eliminates the ability of the soil to support any life.

WHY IS SOIL AERATION SO IMPORTANT?

Soil aeration must replenish the oxygen (0₂) content of the soil air and exhaust the accumulation of carbon dioxide (CO₂). The air that enters the soil from the aboveground atmosphere contains 21 percent 0₂ and somewhere near 0.038 percent CO₂. Normal respiration by turf grass and soil microbes depletes 0₂ content and increases CO₂ content.

Diffusion moves substances from an area of high concentration to an area of low concentration. Gas diffusion rates are highly dependent on the cross-sectional area available for diffusion, so a small reduction in pore size greatly diminishes the movement of gas through it. Thus, loss of aeration porosity (macropores) translates directly into reduced soil aeration. The smaller pores that result from compaction are more likely to be blocked be water films. Both conditions – fewer macropores and more blocked passageways – accelerate formation of anaerobic soils, as characterized by a deficiency of oxygen (anoxia) or a toxic buildup of carbon dioxide.

WATER MANAGEMENT

Horticulturists must consider the soil as the growing media for their plants. Growers go to great efforts and expense to provide an optimum growing environment. A hard compacted soil on a poorly drained site provides a harsh environment for plant growth. Even though most growers would not consider planting trees, ornamentals, or shrubs on such a site, turf growers often plant grass on similar sites. They are expected to manage the soils and produce fine quality lawns, golf courses, sports fields, etc.

The ideal rootzone would contain available moisture for 5 to 8 days; yet maintain high infiltration and percolation rates enough so that water would not stand on the surface for more than a few minutes following a heavy rain event. As the rootzone deviates from this ideal, water management becomes more difficult.

Slowly permeable soils need adequate surface drainage to aid water management, since standing water creates a totally unfavorable rootzone environment for turf. Where standing water consistently occurs after rainfall or irrigation, traditional management practice recommends that drains must be installed to remove excess water. Core aeration also helps get water into a slowly permeable soil by increasing the surface area of the rootzone and by breaking up surface crusts that can impede infiltration. Aeration however provides only temporary improvement in water management and must be repeated when surface crusts and layers re-develop.

Soil aeration is directly affected by the amount of moisture contained within the soil. Soils will reach a point of saturation, which is the level when aeration or the diffusion of air ceases. At this point plant growth is affected and can be detrimental if the soil remains saturated for a period of time. Tests have shown that soils treated with SoilTech increase the amount of moisture contained before reaching saturation, and increasing aeration at lower moisture levels (See Respiration Rate Test).
Before SoilTech was introduced, the best option available to improve water management in the rootzone is combining surface drainage by core aeration and by installing subsurface drains.

CHARACTERISTICS OF COMPACTED SOIL

Soil bulk density is the weight of solid material in a given volume of soil. Bulk density is calculated by dividing the dry weight of a sample by its volume. It is widely believed that soils with a high bulk density and high soil strength reduce infiltration and percolation thus increasing runoff and soil erosion. Increased soil compaction reduces air space thereby increasing bulk density or weight of dry soil in a given space.

Soil strength is a measure of the penetration resistance of a soil. A handheld recording cone penetrometer can be used to measure soil strength. The cone penetrometer measures the load required to push the cone down into the soil, recording the penetration resistance of the soil. This penetration resistance is a measure of soil strength and is a measure of resistance to penetration by root tip elongation. Like bulk density, soil strength, or its resistance to penetration and displacement, increases with compaction. Soils that are compacted have high bulk density and high soil strength.

SOIL STRUCTURE AND POROSITY

The significant reduction in soil bulk density means that an increase in soil pore space will allow for greater infiltration and percolation. Individual particle size increases, thereby creating more porosity in the soil. Problem areas that had recurrent standing water problems following ordinary precipitation events should be eliminated with use of SoilTech (Refer to Arrowhead Sports Complex Test).

The increased infiltration and percolation exhibited by SoilTech in soils composed of water stable aggregates results in reduced runoff during a rainfall and therefore reduced erosion by running water. The aggregates, by virtue of their size and weight, are less readily carried by water and in addition are more stable to the destructive action of raindrops.
Soil scientists agree that a soil with good porosity directly affects soil aeration, water percolation and infiltration. Soil porosity reduces bulk density and aids in the soil water storing capacity. SoilTech agglomerates the fine particles into larger bodies or crumbs providing the proper pore space for the air and moisture, which in turn provides increased germination and/or growth to existing plants.

The wilting point, which is the moisture content of the soil below which plants are no longer able to extract sufficient water from the soil, determines the lower limit of available water for plant growth. The polyelectrolytes in SoilTech usually have no effect on the wilting point of the soil, but sometimes cause a slight elevation, which is usually not objectionable. Since the increase in the moisture equivalent is much greater than the increase in wilting point, treatment with SoilTech results in a substantial increase in the amount of water retained by the soil and available for the plant’s use.

The rate of evaporation of water from the surface is affected by soil structure and also by the presence of organic colloids in the soil. A soil of good structure, such as obtained with the treatment of SoilTech, will be composed of water-stable aggregates and in addition to capillary pores, has a large number of non-capillary pores (Refer to Soil Agglomeration Test and USDA National Soil Tilth Laboratory Tests). The action of these non-capillary pores is to break the continuity of the capillary pores to slow down movement of moisture by capillary action. The transfer of capillary water to the surface of the soil is slowed down, and therefore the loss of moisture by evaporation from the surface is greatly reduced.

SoilTech contains both hydrophilic (water loving) and hydrophobic (water hating) molecules. This is a very important to the efficacy of the molecule as the “water loving” part of the formula is attracting and holding onto as much water as it can. Meanwhile the “water hating” part is trying to get away from the water driving it deeper into the soil profile with the help of gravity, and also providing capillary horizontal pore space.

NUTRIENT MANAGEMENT

The nutrient status of the rootzone may be the second priority of the turf manager. Growth rate, density, root development and color are some of the responses to the turf grass nutrient status of the rootzone. If nutrients are not present in required amounts or are not available to the grass for some reason, then weak turf, poor color and slow recovery will be apparent (Refer to Law of the Minimums and Cation Exchange Capacity).

Soil moisture content, pH, soil structure and biological activity of the rootzone all influence the availability of nutrients. Even though nutrients may be present in adequate amounts, they may not be available to the grass in saturated soils, compacted soils or in soils with very low biological activities. To maintain conditions favorable for nutrient uptake, the turf manager must control the soil moisture content. Saturated root zones result in anaerobic conditions where nutrients are not available and gases toxic to grass roots are produced. Denitrification also occurs in saturated soils.

Compacted soils with poor structural characteristics do not provide adequate nutrients for good growth of turf grasses. After the addition of SoilTech, however, you will see pore space return to your reclaimed soil opening up to both air and water. This will encourage all biological activity to begin to flourish, which is the next step in the remediation program.

Soil microbes play a significant role in the availability of plant nutrients. Nearly all of the nitrogen and most of the phosphorous and sulfur, as well as other nutrients, are bound in soil organic matter. In this form these nutrients are largely, or entirely, unavailable for utilization by grasses. It is only through microbial activity that the vast store of nitrogen and the reserve phosphorous and other nutrients are made available to the grass. Thus rootzone conditions such as compaction, saturation, salinity, acidity, and low organic matter that reduces microbial activity also reduces nutrient availability.

For example, in compacted soils, or in poorly drained soils, populations of microbes shift from those that function under aerobic conditions to those that function under anaerobic conditions. As a result, hydrogen sulfide (H₂S) rather than CO₂ becomes the primary product of decomposition and grass roots deteriorate rapidly.

SOIL STRUCTURE AND DENITRIFICATION

There are many ways that nitrogen can be lost after nitrogen fertilizers are applied. For example, nitrates (NO₃⁻) can be leached deep into the soil. Also, there are gaseous losses of N to the atmosphere, including denitrification (Nitrogen Loss) in wet or compacted soils with loss of N gases, like nitrogen gas (N₂), nitrous oxide (N₂0), and ammonia (NH₃) volatilization losses from ammonium containing fertilizers like urea or ammonium sulfates. Denitrification is favored by anaerobic conditions; thus aeration will reduce those losses from compacted soils.

Nitrogen losses by denitrification in poorly aerated soils can be quite rapid and rather large. Losses between 20 and 500 ppm N per day have been reported. Losses increase as the 0₂ supply declines and the soil temperature and energy supply for soil microbes increase. Undoubtedly, the N deficiency that can occur in warm, wet compacted soils can contribute to poor turf quality. Soils that have been treated with SoilTech should significantly decrease denitrification by allowing the nutrients to be incorporated into the soil quicker and by reducing soil compaction.

SoilTech functions both as an acid and a base (amphoteric) therefore the organic polymer mixture will bind cation and anion nutrients and carry them down into the rootzone. In the case of nitrates and phosphates, leaching will be significantly reduced with the addition of SoilTech immediately after fertilization.

EFFECTS OF SOIL PH

Percolation of a soil depends on the soil particle size and on the chemical composition of the soil material. Soils become acidic or sour, by the oxidation of the organic matter and by selective leaching of salts (alkali and alkaline earth metals) by the passing ground water. Leaching is not altogether bad because this natural process removes unwanted elements. This is characteristic of most areas with higher rainfall.

In high sodic and/or saline soils, this leaching of the alkaline salts is greatly enhanced with the use of SoilTech. The strong negative charge of the polymers dissolves the alkaline salts which then allow the bicarbonates (HCO₃⁻) to leach deeply into the sub layers of the soil profile thus removing them from the root growth areas. The end result is lower bicarbonate levels and reduction in sodium levels because it releases a lot of insoluble calcium very quickly and puts it in cationic form (Ca⁺⁺) and into the soil solution.

The problem of poor soil conditions due to salts or pH can be improved with the addition of various chemicals, but traditionally using this method sometimes takes long periods of time for signs of soil improvement. The addition of SoilTech allows salts to leach deeper into the soil thereby creating a space near the layer of topsoil for improved conditions for plant growth. In the case of soils with poor pH qualities, SoilTech dissolves the alkaline materials, thereby promoting leaching deep into the soil more quickly, decreasing the time required to enable plant growth.

It is easy to visually see the effectiveness of SoilTech by taking core samples in the area to be treated and record the depth of insertion. Perform a ribbon test and note the soil particle size at various depths of the sample. After the SoilTech has been applied for 30 days repeat this same test to evaluate your progress. Check each 30-day period for six months.

CATION EXCHANGE CAPACITY

One of the most important functions of soil is to provide nutrients to the roots systems of plants to support their growth and development. Soil nutrients needed by turf grass and other plants are retained on the surfaces of soil particles and organic matter called exchange sites. The total number of nutrient exchange sites is referred to as the Cation Exchange Capacity (CEC) of the soil. The higher the CEC value, the richer the soil is in the contents of nutrients. The amount of these positively charged cations a soil can hold is expressed in milli-equivalents per 100 grams (meq/100g) of soil. The larger this number, the more cations the soil can hold.

Depending on the amount of clay and humus, soil types have a characteristic amount of cation exchange capacity. Soils have a slight excess of negative charge sites due to the presence of clay particles and organic matter. Thus the higher the clay content and organic matter content, the higher the CEC of the soil.

Cations bind loosely to negatively charged sites on soil particles until they are absorbed by plant roots or exchanged for other cations in the soil solution. Examples of positively charged ions (cations) include: calcium (Ca⁺⁺), magnesium (Mg⁺⁺), potassium (K⁺), sodium (Na⁺), hydrogen (H⁺), and ammonium (NH₄⁺), and aluminum (Al⁺⁺⁺). The group is subdivided into the acidic cations and base cations. The acidic cations are H⁺ and Al⁺⁺⁺. The base cations include Ca⁺⁺, Mg⁺⁺, K⁺, and Na⁺.

BASE SATURATION

The base saturation is the total percent of the exchange sites occupied by the four basic cations; Ca⁺⁺, Mg⁺⁺, K⁺, and Na⁺. Therefore it represents a ratio or percentage of acid:base cations in a given soil. For example if the combined percentages of the four basic cations equals 72%, and the acidic cations equal 28%, the % base saturation is 72%. If the exchangeable sodium levels are higher than 15% of the total cations (acid and base) the result probably would be soil compaction. The soil pH is directly related to the combined % base saturation. Generally pH less than 4.8 will have 0% base saturation. At a 5.3 pH the approximate value is 25%; at 6.2 it is at or near 50%; at 7.1 roughly 75%; at 7.5 around 90%; and at and over a pH of 8.0 the base saturation is 100%.

In areas where rainfall is abundant such as the eastern U.S., the base saturation tends to be lower due to the leaching of the alkaline salts, thereby reducing the soil pH. In the west, where rainfall is scarce, the pH is higher thereby increasing the base saturation of the soil. Note: There are numerous pockets of alkaline soils in the eastern U.S. particularly in areas where limestone is prevalent, or where the water supply is alkaline. In some cases, excess or unnecessary lime applications can cause alkaline conditions.

As mentioned earlier, sodium is included as one of the base cations. Sodium inputs from cheap fertilizers, pesticides, herbicides, and irrigation water are common. High sodium levels result in soil dispersion, poor water infiltration, and possible sodium toxicity to plants.

PLANT NUTRIENT IONIC CHARGE

Plants uptake and utilize both cations and anions. Cations and anions not only differ in the ionic charge of positive or negative, but also in its magnitude (1, 2, or 3).

In the table below, the essential elements are listed in their approximate order of critical concentrations, from greatest to least, from top to bottom. Interestingly, several elements are absorbed as oxyanions, ions composed of the mineral element surrounded by three or four oxygen atoms, giving a net negative charge. Also of interest is the fact that several elements are taken up in different forms.

PLANT NUTRIENT IONIC CHARGE TABLE

Cation (3+)	Cation (2+)	Cation (1+)	Neutral (0)	Anion (-1)	Anion (-2)
	Ca⁺⁺	K⁺		NO₃⁻
	Mg⁺⁺	NH₄⁺		H₂PO₄⁻	HP0₄ ² ⁻
	Fe⁺⁺
Fe⁺⁺⁺			B(OH)₃
	Mn⁺⁺			Cl⁻
	Zn⁺⁺
	Cu⁺⁺
	Ni⁺⁺			MoO₂⁻

From this table, a number of points can be made:

• Almost all elements are taken up as charged ions, with charges of 2⁺, 1⁺, 1⁻, 2⁻.
  
• Absent are all organic compounds of the nutrient elements, indicating that all organic fertilizers must undergo mineralization of nutrients to become available to plants.
  
• Nitrogen may be taken up by plants as either an anion NO₃⁻ (nitrate) or a cation NH₄⁺ (ammonium). Plant preferences for nitrate or ammonium are species specific and are usually related to the natural environment of the species, with plants adapted to bogs, marshes, cold, or acid conditions often preferring ammonium-N, and most other dry land species preferring nitrate-N.
  
• The ionic charge on the orthophosphate ion, whether H₂P0₄⁻ or HP0₄²⁻, is dependent upon pH conditions prevailing in solution. At pH 7.2, they are present in equal concentrations. At pH 6.2, the ratio H₂P0₄⁻:HP0₄²⁻ is 10:1, and at pH 8.2, 1:10.

REQUIRED MINERAL ELEMENTS FOR PLANT GROWTH

The Required Mineral Elements Are:  

Nitrogen (N), Phosphorous (P), Potassium (K), Calcium (Ca), Magnesium (Mg), Sulfur (S), Boron (B), Chlorine (Cl), Iron (Fe), Manganese (Mn), Zinc (Zn), Copper (Cu), Molybdenum (Mb), and Nickel (Ni).

In addition to the essential mineral elements are the favorable elements that promote plant growth in many plant species but are not absolutely necessary for completion of the plant life cycle.

Recognized Favorable Elements Are:

Silica (Si), Sodium (Na), Cobalt (Co), and Selenium (Se).

The other elements that have been proposed as candidates for required or favorable elements include:

Chromium (Cr), Vanadium (V), and Titanium (Ti), although definitive proof is lacking at this time.

The required non-mineral elements, elements taken up as gas or water, which are:
Hydrogen (H), Oxygen (O), and Carbon (C).

Somewhat arbitrarily, a dividing line is drawn between those mineral elements required in greater quantities, macronutrients, and those elements required in smaller quantities, micronutrients. This division does not mean that one nutrient is more important than another, just that they are required in different quantities and concentrations.

Macronutrients: N, K, Ca, Mg, P, and S

Micronutrients: Cl, Fe, B, Mn, Zn, Cu, Mo, Ni

According to the cultural practice perspective only, the primary nutrients are N,P, and K, because they are most often limiting.

All of the other required macronutrient elements are secondary nutrients because they are rarely limiting, and more rarely added to soils as fertilizers.

The ability of soils to supply secondary nutrients to plants indefinitely is subject to the law of conservation of matter and is therefore dependent upon nutrient cycling. Continued plant removal of Ca, Mg, and S requires replenishment just as surely as primary nutrients, but most likely less frequently.

Calcium and magnesium are often supplied by mineral weathering, either of natural soil materials or of ag-lime, ground limestone added to correct soil acidity. Sulfur is often added to soil as either atmospheric deposition (associated with air pollution) or as impurities in fertilizers, particularly common P fertilizers.

To demonstrate that this classification is more responsive to soil ability to supply nutrients than plant requirements, it should be noted that plant requirements for calcium, a secondary nutrient element, is greater than for phosphorous. Calcium is found as a principle exchangeable cation in most soils and an important soluble cation in the soil solution.

Phosphorous, on the other hand, is only slightly soluble in most soils, and many soils (particularly acid and alkaline soils) have the potential for causing phosphorous deficiencies.

Bob Richardson

Restoration Biologist

Soil Technologies, LLC