A nutrient imbalance in soil occurs when the amount of essential nutrients for plants is either too low or too high or when it is insufficient or in excess. This can negatively impact plant growth and soil health:
PLANT GROWTH:
When nutrients are deficient, plants may be stunted or have a reduced yield and quality. When nutrients are in excess, the plant may lose nutrients from the soil.
SOIL HEALTH:
Nutrient imbalances can lead to soil acidification, which reduces the availability of nutrients for plants. They can also change the composition of soil biota, like microorganisms and insects, which can disrupt the soil food web.
ENVIRONMENTAL DEGRADATION:
Nutrient imbalances can contribute to environmental degradation and greenhouse gas emissions. Misuse or overuse of fertilizers can harm soil, water, and human and animal health.
Nutrient imbalance can be nutrient in excess or nutrient insufficient. The build up of surplus nutrients in excess of immediate crop can lead to nutrient losses. This causes an economic inefficiency in nutrient use by farmers and also a source of potential harm to the environment. Water bodies become polluted, air and soil also become polluted, and can also lead to greenhouse gas emission. Some nutrients, like nitrogen, phosphorus, and potassium, are macronutrients that plants need in larger quantities. Other nutrients, like iron, manganese, and zinc, are micronutrients that plants need in smaller quantities.
Some nutrients can compete with others for plant uptake, even when soil levels are sufficient ,while some becomes fixed to the soil. For example, in clay soils, phosphorus can become tightly bound to soil particles, making it less available for plants.
Soil nutrient balance is affected by nutrient management in crops. A poor nutrient management technique results in an imbalance in the soil nutrient status which could have a long-term negative impact on crop production.
The nutrient balance is defined as the difference between the nutrient inputs entering a farming system (mainly livestock manure and fertilisers) and the nutrient outputs leaving the system (the uptake of nutrients for crop and pasture production). Inputs of nutrients are necessary in farming systems as they are critical in maintaining and raising crop and other plant productivity.
EFFECT OF EXCESSIVE NUTRIENTS OR NUTRIENT TOXICITY IN SOIL
Soil nutrients sources can be from fertilizers, soil minerals and organic matter. Soils with excessive organic fertilizer like compost and particularly manure, tend to develop high concentrations of nutrients such as ammonium, calcium, magnesium, potassium and sodium. These soils can also develop high concentrations of bicarbonates, carbonates and hydroxyls. This ( excessive nutrients) can inhibit the uptake of other nutrients ( antagonism and synagism ), resulting in deficiencies. For example, high ammonium can inhibit the uptake of calcium, magnesium and potassium.
High concentrations of base cations like calcium, magnesium, potassium and sodium are associated with increased soil alkalinity.
Highly alkaline soils tend to have a high pH (a measure of acidity), and many nutrients become less available in high pH soils. As a result, plants may exhibit nutrient deficiency symptoms, despite an excess of nutrients in the soil.
Another issue of soils that receive excessive compost is the potential for increased soluble salts to levels that would cause salt toxicity.
Optimum nutrient levels listed on soil test results represent the range at which plant growth is maximized. Nutrient levels that are above optimum do not improve plant growth. In addition, excessive nutrients can cause adverse effects on plant growth, increase the potential for environmental contamination due to leaching, and represents a waste of resources. In particular, above optimum, nitrogen and phosphorus levels can lead to excessive plant and algal growth in waterways that can degrade drinking water, fisheries, and recreational areas. High potassium can lead to an imbalance of base saturation levels as well as high soluble salts. Also, high organic matter levels can cause poor drainage. Areas where lawns or turf are being grown should have organic matter levels less than 5%. In general, organic matter levels greater than 8% in outdoor growing environments are unnecessary and can cause the issues above.
In high tunnels, soluble salts can accumulate to excessive levels because leaching is minimal.
Composted manure is generally higher in salts than composted vegetative matter.
Raw manure can be very high in salts and ammonium and is not recommended for use in high tunnels.
Other effects of excessive nutrients in soil include:
1. PLANT GROWTH:
Too much of any nutrient can prevent plants from absorbing other nutrients, which can lead to deficiencies. It can also cause abnormal growth, such as stunted or excessive growth, leaf discoloration, and necrotic spotting. Apart from these, excessive nutrients, or nutrient toxicity can affect plant growth by causing Wilting: Leaves may wilt , Defoliation: Plants may lose leaves ,
Stress: Plants may become stressed and weakened, making them more susceptible to disease and insects , Scorching: Plants may look scorched and
Cellular damage: Reactive oxygen species (ROS) generated by high levels of micronutrients can cause extensive cellular damage
2. SOIL HEALTH:
Excess nutrients can create high salt concentrations in the soil, which can harm beneficial microorganisms.
3. ENVIRONMENTAL CONTAMINATION:
Excessive nutrients can lead to leaching, which can contaminate the environment.
4. IT CAN ALSO LEAD TO RUNOFF:
Excess fertilizer that plants don’t take up can be carried and deposited by water into watersheds, which can harm wildlife.
5. IT CAN ALSO CAUSE EUTROPHICATION: If a water body has high nutrient levels it is said to be eutrophic; the process is called eutrophication.
High levels of nutrients in waterways can cause harmful algal blooms and loss of aquatic life . The high density of these green algae on the water body will block sunlight from penetrating the water causing larger plants under the surface to die and decompose. Apart from this, the sudden algal bloom can die off quickly, decay by the action of bacteria and cause deoxygenation of the water. This is a major problem of eutrophication. Also, nitrate can cause high growth of cyanobacterias in water. Some species of cyanobacteria (also known as blue-green algae) that flourish under these conditions produce toxins that cause liver, nerve and skin problems in humans and animals.
Eutrophication also encourages the growth of larger plants, such as the floating and invasive water hyacinth (Eichhornia crassipes) which can cover large areas of lakes. When these plants die, they add to the problems of deoxygenation caused by decaying organic material.
6. WATER QUALITY:
Excessive nutrients in water can have a number of harmful effects on water quality. Such harmful effects including:
i. DRINKING WATER TREATMENT:
High levels of nitrogen and phosphorus can cause excessive plant and algal growth in waterways, which can degrade drinking water, fisheries, and recreational areas.
Water that contains large amounts of nitrates is unpleasant to drink and can be toxic to humans and animals. In infants, a condition called
Methohemoglobinemia may result. This condition is also known as “blue-baby syndrome”, it is potentially fatal blood disorder that can occur in infants less than six months old. It is associated with nitrates in drinking water.
In addition, Algae and macrophytes bloom can clog filters, corrode intake pipes, and require more chemicals to treat drinking water.
ii. ALGAL BLOOMS:
When there is too much nitrogen and phosphorus in the water, algae grows faster than ecosystems can handle. This can lead to harmful algal blooms (HABs) that can harm the environment and human health.
iii. REDUCED OXYGEN:
The rapid growth of algae can reduce the amount of oxygen available to aquatic life. This can lead to hypoxia, or “dead zones”, where aquatic life cannot survive.
iv. TOXINS:
Algae can produce toxins that can harm people, animals, and aquatic life. These toxins are released into the water when algae cells die or rupture. Some examples of algal toxins include:
Cyanotoxins: Produced by cyanobacteria, also known as blue-green algae. These toxins can cause skin irritation, nerve damage, and other health effects.
Dinotoxins: Produced by dinoflagellates, these toxins can cause diarrheal shellfish poisoning.
Phycotoxins: Produced by diatoms, these toxins can cause amnesic shellfish poisoning.
v. LOSS OF SPECIES:
When algae die and decompose, it can reduce dissolved oxygen in the water, which can cause organisms to die. If this happens repeatedly, species may be lost from the water.
vi .LOSS OF HABITAT:
Eutrophication can kill off plants that fish depend on for their habitat.
vii. DECREASED VISIBILITY:
Algae can reduce water clarity and visibility, which can make it harder for fish to see prey or predators.
7. WASTE OF RESOURCES:
Using too many nutrients is a waste of resources. Excessive nutrients can cause waste of resources by damaging the environment and harming water quality.
Excess nutrients, mainly nitrogen and phosphorus, cause excessive algal bloom. This results in consumption of large amounts of oxygen, which fish, shellfish, and other organisms need to survive. It
makes water cloudy, reducing the ability of aquatic life to find food. It can also clog the gills of fish and other aquatic organisms that uses gills to breath. It can also block light that is needed for plants, such as seagrasses, to grow. And it produces toxin that can harm people, animals, and aquatic life
CAUSES OF SOIL -NUTTIENTS IMBALANCE
Two main causes of nutrient imbalance include impoper pH and nutrient level. Other causes include various factors such as: imbalanced fertilization, soil compaction, poor root health, and other environmental stresses.
Lack of nutrients will lead to low soil fertility. Thus, causing nutrient deficiency and nutrient deficiency symptoms in plants. Too little or too much of any nutrient can lead to nutrient imbalance.
The following are causes of nutrient imbalance:
A. IMPROPER SOIL pH: pH is the measure of soil acidity or alkalinity. It affect soil health and some nutrient availability for uptake by plant.
Soil that is too acidic or alkaline can affect how plants access nutrients.
CAUSES OF SOIL ACIDITY
a. High rainfall
b. Acidic rain
c. Fertilizers
d. Weathering oxidation
EFFECT OF SOIL ACIDITY
a. It affect crop yield
b. crop suitability
c. crop-plant availability
d. soil microbial activities
Most plants can only survive at neutral pH to slightly alkaline pH (that is, 7.5 to 8.5)
at pH 5.5 or lesser, Al3+, H+ and Mn2+ becomes toxic , while P, Ca2+,MO and Mg3+ becomes deficient in the soil.
At pH 7.5 and above, Fe, P, and Zn becomes deficient, HCO3 becomes excessive and Ca, Mg and K becomes imbalance.
CAUSES OF SOIL ALKALINITY
a. Drought
b. Weathering
c. High concentration of HCO3
FACTORS THAT AFFECT SOIL pH
Soil pH is affected by
a. land use and management
b. vegetation type: The type of vegetation in an area can have great impact on soil pH. For example, forest land are more acidic than grassland. Conversely, the conversion of both forest land and grass land into crop land can affect soil pH. The changes are caused by
I. loss of organic matter
ii. removal of soil minerals when crops are harvested
iii. erosion of soil layer
iv. effect of Nitrogen and sulphur Fertilizers
Note that addition of nitrogen and sulfur can lower soil pH over time. Soil pH that are too high or too low leads to:
i. deficiency of soil nutrients
ii. decline in crop yield
iii. deterioration of soil health
iv. decline in microbial activities.
MEASURES THAT LIMIT OR CORRECT ACIDIFICATION
A. pH outside the desired range:
a. add sulfur to lower pH
b. add lime to increase the pH
-nutrient deficiency at low pH and toxicity include Fe, MN and AL
Nutrient deficiency and toxicity at high pH include CO32-, HCO3-,AlO4 and toxicity.
Also, outside the pH range, some nutrients can be made available. For example, Al at low pH.
HOW TO CORRECT pH
i. Apply the correct amount of nitrogen fertilizer
ii. liming raise pH of acidic soils
iii. Add sulfur to lower soil pH of alkaline soils
iv. Diversify crop rotation to interrupt acidifying effect of Nitrogen fertilizers
v. Application of manure and other organic materials that has high calcium and bicarbonate.
B. NUTRIENT INTERACTION
The essential plant nutrients must be balanced to ensure plant growth and production. Deficiency of one nutrient cannot be compensated by surplus of the other nutrient. Nutrient interact with each other either synagistically to increase the uptake of one nutrient or antagonistically to reduce the uptake of another nutrient.
Mulders chart can be used to determine nutrient interaction. An antagonize element may be present at adequate level and the plant will not have access to it. The only way to make such nutrient available is to add other nutrients that will knock them out and make them available for plant uptake.
Competing of nutrients at uptake site of the root.
Increase K will hinder Mg, B, N and P utilization etc.
C. IMBALANCED FERTILIZATION: Using fertilizers incorrectly or in excess can lead to nutrient imbalances. This imbalance can be minimized by applying the appropriate rate of fertilizer according to the crop’s demand. Increasing the application of nutrients (NPK) using inorganic fertilizers increased the available nitrogen, phosphorus, and potassium contents in soil for for some crops. The use of NPK fertilizers is critical for restoring soil nutrients and closing the yield gap. Soil fertility can also drop along the hills. The drop in soil fertility in the hills is increased by a decrease in organic matter content. Similarly, applying an inadequate amount of K fertilizer over multiple years may lead to K deficit and reduction in crop yield.
D. SOIL COMPACTION: Compacted soil can make it harder for roots to grow and absorb nutrients. Roots that do grow in compacted soil are often shallow and malformed.
Nutrients such as nitrogen, phosphorus, and potassium are non available to crops in compacted soils due to the following factors:
a. Reduced oxygen: Compaction reduces the amount of oxygen in the soil, which affects the availability of nitrogen. When oxygen levels in soil is low, nitrogen in the soil becomes less available to plants by causing denitrification. Low soil oxygen levels results in anaerobic bacteria using nitrate as an oxygen source. The nitrate is converted to gaseous nitrogen oxides or N2 gas. These gaseous forms of nitrogen are then lost to the atmosphere and are unavailable to plants.
b. Low concentrations: Compaction reduces the concentration and mobility of nutrients like phosphorus and potassium in soil solutions. It can reduce the mobility of phosphorus and potassium in soil by making the soil less porous, which limits the movement of nutrients. Compaction can also restrict root growth. Roots are less able to penetrate the soil, thus, limiting their ability to access nutrients and moisture. Compaction can also interfere with drainage. It can cause extended periods of saturation and also reduce permeability (As soil is compacted, the void ratio decreases, reducing permeability).
Soil compaction do affect the soil physical properties and plant growth, and through the effects on aeration all biological soil processes are affected
E. EXCESSIVE LEACHING: Leaching is the process of removing soluble substances from the top layer of soil through the action of precipitation or irrigation. The rate of leaching increases with heavy rainfall, over irrigation, high temperatures, and the removal of protective vegetation.
Leaching can be beneficial for crops by transporting minerals from topsoil down to roots zones. However, excessive leaching can lead to nutrient imbalances, which can cause poor plant growth and reduced crop yield. Leaching removes vital nutrients and micronutrients, such as water-soluble boron, nitrogen etc from the soil, causing potential deficiencies in crops. For example, Boron deficiency result in distorted or misshapen leaves, thickened leaves, brittle leaves, hollow centers in developing curds or heads, abnormal flower development. And Nitrogen deficiency result in poor plant growth and reduced crop yield etc.
F. POOR ROOT HEALTH:
Root health has a significant impact on a plant’s ability to absorb nutrients from the soil. The roots are the primary interface between the plant and its environment and it is the organ plants use for absorbing nutrients from the soil solution. Root diseases or poor root development can make it harder for plants to absorb nutrients. Root health can affects nutrient uptake through the following ways:
a. Root hairs
Roots have thousands of root hairs that increase their absorbent surface area. Damage to these root hairs can make it difficult for the plant to absorb nutrients and water.
b. Morphological ( such as diameter, surface area, cell wall structure, root hairs, and length) and physiological properties ( anatomical features) of roots and their accompanied tissues also affect nutrient uptake and transport. The root traits( Root traits are characteristics of a plant’s roots that can be morphological, physiological, anatomical, chemical, or biological such as root thickness, longevity, lateral root density, root tip diameter etc ) related to the properties also depend on the kinds of nutrients and their mobility in the soil. For example, plants may grow thinner and produce deeper roots to acquire water and nutrients during droughts.
EFFECTS OF NUTRIENT INBALANCE IN SOIL
Some effects of nutrient imbalances in soil include:
a. REDUCED PLANT GROWTH: Plants may not be able to absorb the nutrients they need to grow.
b. SOIL ACIDIFICATION: Soil can become more acidic, which can reduce soil fertility and the availability of nutrients for plants.
c. CHANGES IN SOIL BIOTA: The composition of soil microorganisms and insects can be affected, which can disrupt the soil food web.
d. ALTERED SOIL CHEMISTRY: The availability of nutrients for plants can be reduced
BALANCING SOIL NUTRIENTS
Soil nutrient balance is the equilibrium between the nutrients that enter the soil and the nutrients that leaves the soil. It’s important for maintaining soil health and productivity. Some ways of maintaining soil nutrient balance include:
1. INCREASE SOM: SOM Prevents clay particles from forming soil mass by adding organic matter. SOM improves pore spaces, increases microbial activities, act as sponge to hold more water etc and helps buffer soil pH. Organic matter also improve soil texture, structure, and chemical balance. Organic matter can be added to soil by using compost, manure, or cover crops.
2.COMPOST: Compost helps balance soil nutrients in a number of ways: It can assist in nutrient release. Compost gradually releases nutrients as organic matter decomposes. It assist in converting nutrients into available form. Beneficial microorganisms in compost convert nutrients into forms that plants can use.
Compost also improves soil structure, which helps retain nutrients and allows root systems to access nutrients more effectively. Compost also assist in maintaining Carbon-to-nitrogen ratio. The ideal carbon-to-nitrogen (C/N) ratio for composting is around 30:1, or 30 parts carbon for each part nitrogen by weight.
Other benefits of compost including:
-Preventing soil erosion
-Assisting in stormwater management
-Promoting healthier plant growth
-Conserving water and
-Reducing waste
3. TEST SOIL: A soil test will provide information on the current levels of nutrients in the soil, including nitrogen, phosphorus, potassium and other nutrients. After the test, the amount of nutrients needed can then be calculated and applied so as not to provide in excess.
4. ADD FERTILIZER: After soil test and the soil shows low levels of key nutrients, then additional commercial fertilizer can be applied to revitalize the soil.
5. PROTECT TOPSOIL: The topsoil is the richest horizon with abundance amount of nutrients and microbial activities. When the topsoil is left bare, loss of nutrient from the layer is high. Therefore, with mulch or cover crops, the topsoil layer can maintain its nutrient level.
6. ROTATE CROPS: Rotating crops can help maintain soil nutrients especially when legumineous crops are included in the rotation. Also, planting crops with different root depth can mine nutrients from the various layers of the soil and not overexploit nutrients from a single layer.
7. LIMIT USE OF CHEMICALS: Farmers should avoid using chemicals or limit their usage. They can only choose chemicals unless there’s no other option.
8. MAINTAIN SOIL MOISTURE: Adequate soil moisture can promote microbial populations and activity. Soil moisture is also needed to dissolve the nutrients and put them in available form for plant uptake.
9. MAINTAIN SOIL pH: Maintain the optimum pH for the soil is essential for optimum plant growth.
10. MAINTAIN SOIL AERATION: Good soil aeration can promote microbial populations and activity. Therefore, soil pore spaces must be improved for optimum soil aeration.
