One of the most important soil properties is acidity. The normal growth and development of plants largely depends on it. When liming acidic soils, depending on their acidity, a certain dose of lime is added. Therefore, the acidity of the soil must be known, and also able to determine. Soil acidity can be determined using universal indicator paper, or it is possible, resorting to a simpler method, using indicator plants.
The purpose of our work: to find out whether indicator plants can be used to determine soil acidity.
- The object of our study was the soil.
- The subject of the study is soil acidity.
In accordance with the foregoing, we decided on the objectives of the study:
- Study literature on:
a) what is the acidity of the soil;
b) methods of eliminating soil acidity;
c) what is a hydrogen indicator.
Determine the acidity of soils where indicator plants grow using universal indicator paper.
- Literature review
Soil acidity
Soil is a thin layer of earth that gives life to plants, formed by transforming the surface layers of the lithosphere, by the combined action of water, air and organisms. Soil consists of genetically related horizons that reflect the evolution of soil formation. In it, our "green companions" find support for the roots, nutrients, water, and their growth and development depend on its properties.
One of the important properties of the soil is acidity. It is due to the presence in the soil of organic and mineral acids, physiologically acid salts. Organic acids are formed in the process of decay of the remains of plants and animals in the absence of aeration (air access) of the soil. Such, for example, peatlands. Physiologically acid salts are understood as mineral fertilizers introduced into the soil, such as ammonium sulfate, ammonium chloride, ammonium nitrate, which increase the acidity of the soil as a result of systematic use, which is not accompanied by liming. Also, acids in the soil accumulate when precipitation, spring meltwater, calcium and magnesium are washed out of it. This process is characteristic of podzolic soils, therefore they have, as a rule, high acidity. An additional factor in increasing soil acidity is acid rain, containing sulfuric and partially nitric acid.
The acidity of the soil is directly related to the absorption by the plants of the nutrients necessary for their growth. Too acid and alkaline soils are unfavorable for most plants because they dissolve nutrients poorly. For example, on acidic soils, a significant part of the phosphorus fertilizers introduced goes into an insoluble, difficult to reach form for plants. Also, in acidic soils, the solubility of compounds of iron, manganese, aluminum, boron, copper, zinc; with an excess of these elements, plant productivity decreases. At the same time, high acidity lowers the availability of such an important trace element as molybdenum.
Bacteria are poorly developed in acidic soils. This means that the transition of humus to soluble mineral salts slows down. In addition, acidic soils do not dry well in spring, and then quickly dry out and become crusty. Strongly acidic and acidic soil is not tolerated by earthworms, the absence of which significantly reduces its fertility.
Chemical land reclamation.
Chemical reclamation is carried out to improve the quality of soils with high acidity or alkalinity. In the first case, liming is carried out, in the second, gypsum plating.
Liming acts on the soil in many ways: it improves the activity of nodule and nitrogen-fixing bacteria, increases the coagulating ability of soil colloids, and therefore increases the effectiveness of mineral fertilizers by 30-40%; improves soil structure, their water and air regime; contributes to the development of the root system of plants.
The main lime fertilizer is ground limestone CaCO3. Water-insoluble calcium carbonate under the influence of carbon dioxide (the product of the vital activity of microorganisms) and water turns into soluble calcium hydrogen carbonate, which is hydrolyzed by anion. The resulting hydroxide anion also neutralizes the excess of hydrogen cations in acidic soils.
Cultivated plants react differently to soil acidity and liming. Alfalfa, cabbage, clover, beets are very sensitive to soil acidity, they need a medium close to neutral (pH 6.2-7.2), so the soil must be liming. Wheat, barley, corn, peas, beans, vetch, turnip, rutabaga grow well with a slightly acid reaction (pH 5.1-6.0) and liming. Rye oats, timothy, buckwheat tolerate moderate acidity (pH 4.5-5.0) and respond positively to high doses of lime. Potatoes, flax, and sunflowers easily tolerate moderate acidity and require liming only on strongly and medium-acid soils. Lupine, tea bush are not very sensitive to soil acidity.
In addition to limestones, other carbonate minerals are used as lime fertilizers: calcareous tuff, dolomite, chalk.
Hydrogen indicator
The acidity of the soil denotes pH, and its degree is the corresponding figure.
PH is a hydrogen indicator, where the r-initial letter of the Danish word potenz is a mathematical degree; the letter H is the hydrogen symbol. This concept was introduced in 1909. Danish chemist S. Serensen to express the concentration of H + ions in solution. pH is the decimal logarithm of the concentration of H + ions taken with the opposite sign: pH = - Ig (H). Depending on the concentration of H + ions in the solution, the medium may be acidic, alkaline or neutral.
Distilled water is considered neutral. As a complex electrolyte, it slightly dissociates into H + and OH- ions, which are in equilibrium with the undissociation of Н2О molecules: Н2О – Н + + ОН-
It was established by experience that in 1 liter of water at room temperature (220 ° C) only 10–7 mol / L H2O undergoes dissociation and 10–7 mol / L H + ions and 10–7 mol / L OH– ions are formed. pH = - Ig (10-7) = 7
Thus, if pH = 7, = the medium is neutral;
pH <7, > acidic medium
pH>, < alkaline medium.
The pH of the solution can be determined using a universal indicator paper, which is a regular filter paper impregnated with a solution of a universal indicator. It is designed to determine the pH in the range from 1 to 10. Depending on the pH of the solution, the universal indicator paper takes on a different color, according to which the pH of the solution is determined using a standard color scale. Like an aqueous, soil solution with a pH of 7 is considered neutral if pH> 7 is alkaline and at pH <7 is acidic.
Different plants react differently to the acidity of the soil in different ways: some require acidic soils for their development, such plants are called acidophiles; others need close neutral soils; still others prefer alkaline soils; they are basophils. Each type of plant can exist only in the range of soil acidity (pH) inherent to it. Therefore, some plants act as indicators of soil acidity.
The so-called eurytopic plants normally develop over a wide range of acidity in soil solutions (from 3.0 to 7.5 and from 5.0 to 9.5). Therefore, they cannot be used as indicators of soil acidity. These plants include: wild strawberries, creeping buttercups, Mazibela, bird buckwheat, field bindweed.
Experimental part.
"Determination of soil acidity using plants - indicators and universal indicator paper."
Equipment and reagents: a tablespoon or a baby scoop, tweezers, a porcelain mortar and pestle, scales, weights, universal indicator paper, beakers (100 ml.), Sample 1 N KCL solution.
Working process:
Determination of soil acidity using a plant indicator.
. We determined the site where the plant is an indicator, and the acidity of the soil on it using table 2.
Determination of soil acidity using universal indicator paper
a) The selection of soil samples, their storage and preparation for analysis
. Took 5 - 6 tablespoons of soil in different places of this site.
Note: In the forest, on the lawn, soil samples are taken from a depth of 5 - 10 cm. In the field, in the garden, in the meadow, the upper 15 - 20 cm of soil are used for sampling.
. Put all the samples in a plastic bag.
. Be sure to fill in the label indicating the date and place of sampling, plant indicator, your name.
. They put the label in a plastic bag with selected soil and brought it to the storage room.
Note: since the soil in the plastic bag is very wet until the writing on the label disappears, stick it on both sides with tape (or put it in a small plastic bag).
. No more than a day later, the contents of the bag were poured onto a sheet of thick paper or a sheet of plastic film, mixed thoroughly and dried in air for 2 to 3 days, avoiding direct sunlight.
Note: It is not recommended to dry the soil on paper with text or drawings, as well as on any surfaces covered with paint. The storage room should be dry, well ventilated, free from air fumes of acids and gases.
. After drying, all foreign impurities (leaves, roots, small stones, etc.) were removed from the soil mixture with tweezers.
. They ground the soil in a porcelain mortar with a pestle until the diameter of the lumps exceeds 1 - 2 mm.
The crushed soil was placed in the same plastic bag along with the label.
a) Preparation of salt extract from the soil.
. Weighed on the scales of 10 g. Air - dry soil and placed it in a beaker.
. 25 ml were added to the sample. 1 n KCI solution (soil: water ratio = 1: 2.5).
. Shaken the mixture and left for a day.
. The next day, the solution was mixed and analysis started.
Note: for the preparation of 1 N. KCI solution must be dissolved in water 74.56 potassium chloride and bring the volume in the volumetric flask to 1 liter. The solution should be prepared at least a day before the analysis.
C) Determination of pH of salt extract using universal indicator paper.
. In a glass with a small amount of hoods, a strip of universal indicator paper was lowered.
. The pH value was determined by its color (with an accuracy of 0.5 pH) using a standard color scale showing the color of the paper at various pH values. The experiment was carried out three times.
Presentation of work results.
Conclusions
In the course of practical work, the acidity of the soil was determined using an indicator plant and universal indicator paper. It can be seen from the results of the work that the pH of the salt extract is within the limits of soil acidity typical of the plant. Therefore, these indicator plants (black currant, raspberry, warty quinoa, compact sphagnum, poisonous ranunculus, coltsfoot) can be used to determine the acidity of the soil.