about soil nutrients

SOIL TESTING

Soil Testing

Soil testing provides valuable information on pH and plant-available nutrients. Test your soil before planting and every two to three years thereafter. Inexpensive soil test kits are unreliable. To accurately determine your soil characteristics and the proper amount of lime and fertilizer to apply, contact the NC Department of Agriculture and Consumer Services (NCDA&CS). The accuracy of these reports, however, depends on the quality of the sample submitted.

Tips for Collecting a Good Soil Sample

·         Collect samples with stainless steel or chrome-plated tools. Using brass, bronze, or galvanized materials could contaminate the sample.

·         The bucket in which material is collected should be made of plastic.

·         Make sure the collection bucket is clean because even small amounts of residual lime or fertilizer can affect the test results.

·         Avoid taking samples from areas that are obviously different from the norm, such as wet spots, compost piles, animal urine spots, and brush piles, or from under eaves or sites where trash has been burned.

·         Remove large pieces of organic material, such as roots, stalks, and leaves, from the sample.

·         For gardens, new lawns, and other cultivated areas, sample to the depth the soil has been, or will be, tilled. For established lawns, collect the sample 2 to 4 inches deep. For trees and shrubs, take a sample to a depth of 6 inches near the plant's drip line. Even if the soil looks the same, take separate samples for flower beds, vegetable gardens, fruit orchards, shrub borders, and lawn areas.

·         If using a trowel or spade, dig a hole, then take a slice of soil down one side. Repeat this procedure in five to eight spots for each area to be tested. Mix these cores together to obtain one composite sample. If the soil is very wet, it could be more difficult to mix, but do not attempt to heat the soil to dry it.

        Soil testing includes determination of PH, EC, organic carbon, nitrogen, phosphorus, potassium, sulpher, boron, zinc, iron, calcium and magnasium.

Soil pH

Soil pH is a measure of the soil’s relative acidity or basicity. The pH scale ranges from 0 to 14. A pH of 7 is a neutral state, representing the value found in pure water. Values above 7.0 are basic, while values below 7.0 are acidic. The pH scale is logarithmic, meaning each unit has a 10-fold increase of acidity or basicity. Thus, compared to a pH of 7.0, a pH of 6.0 is ten times more acidic, and a pH of 5.0 is 100 times more acidic.

North Carolina soils tend to be acidic, as are nearly all soils in the Southeast. These soils were acidified over thousands of years by inputs of acids from atmospheric sources (carbonic, sulfuric, and nitric acid), the decay of plant and animal residues, and removal of basic cations by the natural processes of leaching. If our native soils are not limed (basic), the pH is often in the 4.5 to 5.5 range.

THE IMPORTANCE OF SOIL ORGANIC CARBON

The carbon cycle is a fundamental part of life on earth. ‘Soil organic carbon’ (SOC) – the amount of carbon stored in the soil is a component of soil organic matter – plant and animal materials in the soil that are in various stages of decay.

Soil organic carbon is the basis of soil fertility. It releases nutrients for plant growth, promotes the structure, biological and physical health of soil, and is a buffer against harmful substances.

Soil organic carbon is part of the natural carbon cycle, and the world’s soils holds around twice the amount of carbon that is found in the atmosphere and in vegetation. Organic material is manufactured by plants using carbon dioxide from the air and water. Plants (and animals, as part of the food chain), die and return to the soil where they are decomposed and recycled. Minerals are released into the soil and carbon dioxide is released into the atmosphere.

Soil organic carbon accounts for less than 5% on average of the mass of upper soil layers, and diminishes with depth. According to the CSIRO, in rain-forests or good soils, soil organic carbon can be greater than 10%, while in poorer or heavily exploited soils, levels are likely to be less than 1%.

SOIL MACRONUTRIENTS

Nitrogen

Nitrogen is a major constituent of several of the most important plant substances. For example, nitrogen compounds comprise 40% to 50% of the dry matter of protoplasm, and it is a constituent of amino acids, the building blocks of proteins.^[8] It is also an essential constituent of chlorophyll.^[9] Nitrogen deficiency most often results in stunted growth, slow growth, and chlorosis. Nitrogen deficient plants will also exhibit a purple appearance on the stems, petioles and underside of leaves from an accumulation of anthocyanin pigments.

Microorganisms have a central role in almost all aspects of nitrogen availability, and therefore for life support on earth. Some bacteria can convert N₂ into ammonia by the process termed nitrogen fixation; these bacteria are either free-living or form symbiotic associations with plants or other organisms (e.g., termites, protozoa), while other bacteria bring about transformations of ammonia to nitrate, and of nitrate to N₂ or other nitrogen gases. Many bacteria and fungi degrade organic matter, releasing fixed nitrogen for reuse by other organisms

Phosphorus

Like nitrogen, phosphorus is involved with many vital plant processes. Within a plant, it is present mainly as a structural component of the nucleic acids: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), as well as a constituent of fatty phospholipids, that are important in membrane development and function. It is present in both organic and inorganic forms, both of which are readily translocated within the plant. All energy transfers in the cell are critically dependent on phosphorus. As with all living things, phosphorus is part of the Adenosine triphosphate (ATP), which is of immediate use in all processes that require energy with the cells. 

Phosphorus deficiency can produce symptoms similar to those of nitrogen deficiency, but as noted by Russel: 

Potassium

Unlike other major elements, potassium does not enter into the composition of any of the important plant constituents involved in metabolism, but it does occur in all parts of plants in substantial amounts. It seems to be of particular importance in leaves and at growing points. Potassium is outstanding among the nutrient elements for its mobility and solubility within plant tissues. Processes involving potassium include the formation of carbohydrates and proteins, the regulation of internal plant moisture, as an accelerator of enzyme action, and as contributor to photosynthesis, especially under low light intensity.

Potassium regulates the opening and closing of the stomata by a potassium ion pump. Since stomata are important in water regulation, potassium regulates water loss from the leaves and increases drought tolerance. Potassium deficiency may cause necrosis or interveinal chlorosis. 

Potassium serves as an activator of enzymes used in photosynthesis and respiration. Potassium is used to build cellulose and aids in photosynthesis by the formation of a chlorophyll precursor. Potassium deficiency may result in higher risk of pathogens, wilting, chlorosis, brown spotting, and higher chances of damage from frost and heat.

SOIL MICRONUTRIENTS

Sulfur

Sulfur is a structural component of some amino acids (including cystein and methionine) and vitamins, and is essential for chloroplast growth and function; it is found in the iron-sulphur complexes of the electron transport chains in photosynthesis. It is needed for N₂fixation by legumes, and the conversion of nitrate into amino acids and then into protein.

In plants, sulphur cannot be mobilized from older leaves for new growth, Symptoms of deficiency include yellowing of leaves and stunted growth.

Iron

Iron is necessary for photosynthesis and is present as an enzyme cofactor in plants. Iron deficiency can result in interveinal chlorosis and necrosis. Iron is not a structural part of chlorophyll but very much essential for its synthesis. Copper deficiency can be responsible for promoting an iron deficiency. It helps in the electron transport of plant.

Boron

Boron is absorbed by plants in the form of the anion BO3− . It is available to plants in moderately soluble mineral forms of Ca, Mg and Na borates and the highly soluble form of organic compounds. It is available to plants over a range of pH, from 5.0 to 7.5. It is mobile in the soil, hence, it is prone to leaching. Leaching removes substantial amounts of boron in sandy soil, but little in fine silt or clay soil.

Zinc

Zinc is required in a large number of enzymes and plays an essential role in DNA transcription. A typical symptom of zinc deficiency is the stunted growth of leaves, commonly known as "little leaf" and is caused by the oxidative degradation of the growth hormone auxin.