Soil acidity is a soil condition that occurs when there is gradual depletion and replacement of soil basic cations (Ca, Mg, K) by cations held in colloidal soil reserves. The replacement of the basic cations leads to a decrease in soil PH. pH stands for the potential (p) of hydrogen ion (H+) in water. It is a way of calibrating the concentration of H+ in a solution. Soil pH is the pH of soil water. The pH measurement is based on a scale from 1 to 14. With pH 1 denoting an acidic substance while pH 14 is used to denote a basic.
pH of 7.
0, the mid point of 0 and 14, is used to denote a neutral soil; neither acidic nor basic since there is a balance of hydrogen (H+) ions and hydoxyl (OH-) ions. pH, by definition, is the negative logarithm of the hydrogen ion activity; this therefore means that a unit change in pH scale will represents a ten-fold rise in the amount of acidity or basicity of a suspension or solution.
During the process of acidification there is a decrease in pH. This is due to the release of positively charged ions from the organic matter and clay minerals.
The concentration of potassium , magnesium and calcium in soil solution increases considerably. Once the cation exchange surface (in this case organic matter and clay surfaces) is depleted of the ions, the concentration of the soil solution becomes low and the pH is then largely determined by the weathering rate. pH of soil falls below 6. 0, the availability of some nutrients like as phosphorus, potassium, calcium, and magnesium to plants is decreases.
However the availability of most metallic micronutrients like zinc, manganese, copper, and iron increases.
Some other nutrients that is not necessary for plant like aluminum is also increased. As the soil pH decreases Aluminum, one of soils principle constituent, dissolves more this makes it more available for uptake by plants. Increased uptake of aluminum is toxic to plants. Aluminum toxicity to plants is the main concern with acid soils in our region. Some other problems associated with acidic soils include: Manganese toxicity to plants, Calcium and magnesium deficiency, molybdenum deficiency in legumes, poor bacterial growth (necessary for proper growth of some plants) and reduced nitrogenous transformations.
In tomato plant, calcium is one of the most important mineral. Tomatoes require large quantities of calcium which is estimated at around 1. 7 kg of calcium which is removed in every tonne of the crop produced. The quantity taken up by the plant however depends primarily on three factors: the quantity available in the soil; the rate of water movement into the plant; and the acidity or basacity of the soil. Calcium is required in tomatoes for vigorous leaf and root development, and canopy growth.
It is also responsible for the proper formation of cell walls and cell membranes in the tomato plant as well as helping the fruit retain firmness as it develops. Moreover, it aids in pollen germination, regulation of some intracellular enzyme systems and also influences the resistance of tomato to the development of blossom end rot. A constant supply of calcium is therefore necessary throughout the plant’s life. But soil acidity reduces this likely hood leading to immature flowering and watery tomato fruits.
Soil acidity, by virtue that it makes calcium unavailable to tomato plants, therefore affects proper growth and development of tomato plants. Aims The aim of this research paper is to show through experiments and practical demonstrations that soil acidity affects proper growth and development of tomatoes. It also aims at showing that calcium uptake by the tomato is partly influenced by soil acidity. Hypothesis Soil pH is necessary for growth and development of tomato plants Procedure
In one set of experiment to test for effect of calcium deficiency on tomato plant, two sets of tomato plants were planted in an experimental setting, factors such as levels of other nutrients, temperature, humidity, the hours of exposure to sunlight, water availability were controlled to enable accurate analysis and deductions from the data acquired. The soil used for the experiment was one with a pH of 6. 4(for the control experiment) and another soil with an acidic constitution having a pH of 5. 5.
In one set of experiment (which was the control for the experiment), tomato plants were denied calcium for calcium for a relatively short time; while in the other calcium was supplied. The variety of tomato used in this case was the ‘Capita’ variety. The seeds were all germinated in a controlled environment and were cultivated for 28 days. At this stage, the plants were growing in 12 liter containers. Then the nutrient supply for these plants was changed such that calcium was supplied to the control experiment and denied in the experimental tomatoes for seven days.
Samples of plants in each group were harvested before and after the change in the nutrient supply and studied seven days after application of calcium to the specimen. Analysis The reduced rate of photosynthesis which is recorded in the experiment would have an effect on plant growth and development. The acidic nature of the soil coupled with nutrient denial for the first seven days to the plants in the first experiment inhibited calcium uptake by the plants. The sample tomatoes taken from the experiment before introduction of calcium recorded less accumulation of dry matter over the time than did the controls.
After the seventh day and the change in nutrient constituents of both the control and the experiment, there was little change in the leaf formation of the control experiment while the experiment did not appreciate (recover fully) in leaf formation. The experiment failed to accumulate dry matter at the same rate as the controls. This showed that calcium is also necessary in early development of root and stem. The experiment could not accumulate more dry matter because of poor root development.
The effects of acidity on the specimen could be seen because after the seventh day there was a small increase in the total leaf area while in the control experiment there was a total reduction in the total number of the leaves as well as the surface area of the leaves. Discussion Out of laboratory, in normal field practice, field-grown tomatoes are usually planted into soil with a pH of between 6 and 6. 5. However, as soil pH declines, the availability of calcium declines, especially when the soil pH goes below pH 5. 5.
In such a situation, the tomato plants have little soil reserves of calcium to draw on, so its uptake is restricted. Most of the calcium which is taken up by plants enters the plant as part of mass flow, along with the water that is used in transpiration. When the level of soil water is low, less calcium is taken up by the plant since less water enters the plant. Humidity control in the experiment is meant to prevent water loss hence allowing more of calcium to be taken up by plants. In normal field planting practice, tomatoes are sown in polyethylene-mulched beds.
They were sown when the garden temperatures were consistent at 50° F in plastic mulch beds which help to maintain a high degree of water and fertilizer use efficiency. Seedlings are thereafter transplanted 3 to 5 weeks after sowing. Spacing for the tomatoes is done at approximately 5-7 feet between rows, and 3-4 feet in the row. However if the tomatoes are to be pruned then a Spacing of 4-5 ft between rows and 15-24 inches between plants is required. For early root development, 10:52:17 compound fertilizer can be used in application solution of 3-4 lbs per 50 gallons of transplant water.
The sown seeds should then be kept in shade for the first week and are carefully monitored to maintain proper watering, nutrition and diseases detection. The soil pH should also be tested in most cases to ensure proper application of required nutrients. This can be done by use of commercially available electronic pH meter, in which a rod is inserted into moistened soil and it measures the concentration of hydrogen ions in the soil, other ways of measuring soil pH are: to observe the predominant plants, some plants are associated with acidic soils while others are associated withy basic soils.
For example Erica, Rhododendron, Ericaceae species, Betula (birch) are found in acidic areas and are referred to as Calcifuge plants. Fraxinus, Honeysuckle, Buddleia, Cornus spp (dogwoods), Lilac and Clematis spp. Calcicole are mostly got in lime (basic) soils. Observing symptoms that might indicate acidity or alkalinity of soil is also another method. There are some occurrences of some plant diseases that may be caused by conditions of either alkalinity or acidity of the soils. Other more common methods are the use of barium sulfate powder which is mixed with a sample of soil containing water.
The change in color indicates either the acidity or alkalinity of a soil sample. Litmus papers can also be used. Soil acidity as seen, in tomato plant experiment is responsible, by deduction, for poor leaf and roots development, susceptibility to some bacterial infections like blossom end rot, poor fruit formation, immature falling off of fruits amongst other problems that can be directly attributed or indirectly attributed to the effects of soil acidity. Conclusion Soil acidity can be caused by a number of factors.
These factors can either be the soil forming factors of the nature of the parent material, the type of climate, types and availability of living organisms, topography of the land and the time it has taken since its formation or environmental or human factors. Soil acidity as seen in the research leads to serious inhibition of calcium and other trace elements necessary for proper development and growth of tomato plants. Calcium deficiency also leads to poor fruit and stem development as well a leaving the tomatoes prone to fungal attacks.
Calcium can be supplied to plant in a number of ways; Dry-application of fertilizer can work in the period before planting. This will provide the tomato plants with a reserve of calcium and other nutrients that are necessary for growth. However, if specific nutrient deficiencies become apparent as the plant matures then application by spraying the leaves may be appropriate. The fruits can also be sprayed to maximize the quality the fruit produced. Such fruit sprays, especially with calcium, reduce likelihood of an attack by blossom end rot.
One of the ways to reduce soil acidity is by application of lime and other alkaline based fertilizer. The choice of fertilizer to be applied should be based on crop nutrient demands as well as the stage of crop growth. Excessive fertilizer application is also not recommended because it often results in salt buildup, phytotoxic effects on plant growth as well as ground water contamination.
Dustman, R. B. Effect of Acid Soil on Early Growth of Tomato Plants. Botanical Gazette, Vol. 77, No. 4, 1924.
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