Soil Acidity and Alkalinity are both termed soil reaction or soil condition or soil pH. It is important these two parameters are known because they have great effects on crop yield.
They determine the type of crop to be grown on a piece of land because there are some crops that prefer acidic soils while some prefer alkaline soil. Also, they control the availability of the essential nutrients and minerals and the abundance of soil microorganisms. Adversely, high pH can disrupt the soil structure.
A farmer must determine the reaction or condition of the soil before planting as it will guide the farmer to know the type of crop to be grown on the land or to make correction, if needed, to suit his choice of crop to be planted. The standard soil reaction scale ( soil pH) ranges from 1 to 14, the soil reaction is acidic when it is below 7 but alkaline when it is above 7. At 7, the soil reaction is regarded as neutral but in practical terms soils between 6.5-7.5 is regarded as being neutral.
A soil is said to be acidic when the soil reaction is below 7, soils in the range 5.6-6.0 are moderately acidic and below 5.5 are strongly acidic. The more Hydrogen ion held on the soil, the greater the acidity of the soil. Soil acidity is formed as a result of the inputs of carbonic, sulfuric and nitric acid from the atmosphere, plant exudates and the decay of plants and animals residues. Also caused by the continuous use of acid forming fertilizers. It is common in areas with high rainfall.
Acidic soils are deficient of essential plants nutrients such as Calcium, Magnesium, Phosphorus and the minor nutrients like Manganese, Iron and Aluminum become toxic. Crops grown on acidic soils must be able to contend with high level of Aluminum and Manganese, also low availability of Phosphorus, Calcium and Magnesium.
EFFECTS OF SOIL ACIDITY
Soil acidic leads to the following problems
• Aluminum Toxicity
• Manganese Toxicity
• Iron toxicity
• Calcium deficiency
• Magnesium deficiency
• Molybdenum deficiency
• Very slow organic decomposition
• Decrease in Calcium and Phosphorus availability.
HOW TO CORRECT SOIL ACIDITY
When a particular soil is acidic, it can be corrected to suit ones choice for planting. This can be done using the following methods:
• Addition of organic matter
• Addition of wood ash
• Liming: This is the traditional method used to correct soil acidity and to improve soil productivity. Common liming materials are: limestone, dolomite, hydrated lime, quicklime,
Alkaline soils are soils with high soil reaction (pH) above 8.0, they are mostly clay soils with poor structure and low infiltration capacity. They have hard calcareous layer of about 0.5 to 1 metre depth. Alkaline soils also called Sodic soils contain sodium carbonate which causes the soil to swell and difficult to settle. They are mostly found in arid areas (region with uneven rainfall) . They have high salt content.
EFFECTS OF ALKALINE OR SODIC SOILS
• Due to the presence of high content of salt, it causes an osmotic pressure in plants leading to plasmolysis ( the contraction of the protoplast of a plant cell as a result of loss of water from the cell.)
• The quality of water produced to the plants are reduced due to the presence of salt.
• Inability of the plant to absorb nutrients needed from the soil.
• The alkalinity causes corrosive action on the bark of roots and stems.
• Sodium ion has an adverse effects on the plant metabolism.
• The soil has low infiltration rate.
• Rain water stagnates in the soil easily.
HOW TO CORRECT SOIL ALKALINITY
An alkaline soil can be corrected to suit planting conditions through the following ways:
• Good drainage to allow the salts drain with fresh water.
• Leaching and flushing out of the salts from the soil by keeping the soil free of vegetation for about a year to accumulate enough water to penetrate beyond the root depth.
• Addition of gypsum or sulphur to the soil.
THE SOIL pH OF COMMON CROPS
Individual crop has its own specific soil pH some crops can also thrive well on acidic and slightly acidic soil to slightly alkaline soil, these crops are:
• Pineapple (4.5-5.5)
• Egg plant (5.5-6.5)
• Watermelon (6.0-6.8)
• Potatoes (4.5-6.0)
• Tomatoes (5.5-7.5)
• Black berry (5.0-6.0)
• Blue berry (4.5-6.0)
• Raspberry ( 5.5-6.5)
• Peanut (5.0-7.5)
• Garlic (5.5-7.5)
• Radish (6.0-7.0)
• Sweet potatoes (4.5-5.5)
• Beans (5.5-7)
• Cabbage (5.5-7)
• Onion (5.5)
• Grape (5.5-6.5)
• Cassava (5.5-6.5)
• Rice (6.0-6.7)
These values can only be gotten through soil testing, farmers are hereby implored to carryout soil test to know if the soil is good enough for the crop growth.