The factors which influence the availability of nutrients in the soil include the following:
a) Soil pH: The degree of acidity or alkalinity of the soil affects the availability of nutrients, both in the soil and also to plants.
- A low pH (high acidity) will encourage the disintegration of clay minerals like calcium, iron and aluminium, which are leached away from the soil.
- At high pH (high alkalinity), calcium and magnesium ions accumulate in the soil, and this affects the growth of plants.
- A low pH also reduces the activities of soil living organisms which aid the decomposition of organic matter.
b) Concentration of Other Nutrients
- The presence of certain element(s) in high concentration may prevent the absorption or utilisation of other elements.
- The concentration of nitrogen and phosphorus in the soil results in the non-availability of potassium.
- This condition results in retarded growth, low yield or even death of the plant.
- This is the removal of nutrients from the top soil to the inner parts of the soil beyond the reach of the roots of plant.
- It results in the loss of nutrients such as calcium, magnesium, potassium from the top soil in solution.
- It also results in the accumulation of aluminium and hydrogen ions which become acidic and toxic to plants.
d) Crop Removal
- Nutrients are removed from the soil by crops for growth, development and production.
- When the crops are harvested, the nutrients contained in the plants are never returned to the soil.
- The rapid removal of nutrients from the soil by continuous cropping completely deprives the soil of such nutrients.
e) Oxidation and Reduction of Organic Material
- Some compounds such as ammonium radicals are oxidised to gaseous ammonia.
- Nitrates are also reduced to molecular nitrogen or oxides of nitrogen by denitrifying bacteria.
- These products (i.e ammonium radicals and nitrates) which escape into the atmosphere in form of gases make the soil become poorer in nutrients.
- It exposes the soil to erosion which can wash away plant nutrients in the soil.
- It burns the organic matter content of the soil, thereby reducing the amount of nutrients in the soil.
- It kills or reduces the number of soil organisms which aid decomposition of materials, and consequently, most nutrients may not be available to the soil.
g) Soil Texture
- Fine texture, such as clay and silt, ensures the availability of nutrients in the soil.
- But coarse texture like sand prevents the availability of nutrients in the soil.
- Coarse texture encourages the leaching of nutrients from the soil.
- Heavy rainfall causes the washing or carrying away of top soil which is rich in plant nutrients.
- Top soil can also be blown away by winds, resulting in nutrient reduction in the soil.
i) Soil Moisture Content
- Soil moisture content determines the level of nutrients in the soil.
- High level of soil moisture can lead to toxicity of nutrients in the soil.
- High moisture content can lead to soil erosion that can wash away nutrients in the soil.
- Moderate moisture in the soil ensures adequate availability of nutrients in the soil.
- Very low soil moisture leads to dryness or non-availability of nutrients for plants.
j) Level of organic matter/microorganisms in the soil
- High level of organic matter and micro-organisms lead to adequate availability of nutrients in the soil.
- High level of organic matter ensures availability of water in the soil and vice versa.
- High level of micro-organisms the soil ensures good growth for crop plants.
- High level of organic matter in the soil helps to prevent soil erosion.
- Adequate level of organic matter improves the activities of microorganisms in the soil.
- Organic manure also helps to improve the structure of the soil.
- It also reduces rapid soil temperature fluctuations.