Forestscan be referred to as groups of trees and other plants in a large densely wooded area. The two main categories of forests are natural forests, which grow under no human influence and artificial forest, which have been planted by humans. Both types of forests are very beneficial to humankind and to the environment in so many ways.

IMPORTANCE OF THE FORESTS

Forests highly essential for humans and animals’ survival, from the air we breathe through the food we eat to the wood we use. Besides providing habitats for animals and livelihoods for humans, forests also offer watershed protection, preventsoil erosionand mitigate climate change.

Any activities performed by humans involve forests, either directly or indirectly. Some are easy to figure out – fruits, paper and wood from trees, and so on. Others are less obvious, such as by-products that go into everyday items like medicines, cosmetics and detergents.

The forests provide ecosystem services that are critical to human welfare. These include:

• Absorbing harmful greenhouse gasses that produce climate change. In tropical forests alone, a quarter of a trillion tons of carbon is stored in above and below ground biomass
• Providing clean water for drinking, bathing, and other household needs
• Protecting watersheds and reducing or slowing the amount of erosion and chemicals that reach waterways
• Providing food and medicine
• Serving as a buffer in natural disasters like flood andrainfalls
• Providing habitat to more than half of the world’s land-based species

1. Bring Rainfall: Forests are responsible for rains on the land. Due to forests, the clouds get cooled and convert to rainwater. So one can notice heavy rainfall in the areas of forests and around. Forests slower the monsoon currents (winds) and let the clouds move slower over land. They also provide a suitable low temperature for the water vapour in the clouds to convert into water droplets and cause rain. Hence there are no rains in the deserts.
2. PreventSoil erosion: Soil erosion is an everyday natural activity happening due to winds and floods. Growing forests help minimise this soil erosion in the nearby farms. The importance of soil is too much that we cannot afford to lose the fertile top layers. This layer of soil is essential to grow crops and trees.
3. Reduce the effect of natural calamities: In case of the natural disasters like the tsunami, floods, hurricanes, cyclonic winds. Presence of abundant forests helps us minimise the effects of these disasters. Hence when there was tsunami disaster, the areas with many trees at the seashore had less damage than regions without any trees.
4. Home for animals(Ecosystem):Looking at it beyond our narrow, human – not to mention urban – perspective, forests provide habitats to diverse animal species. They are home to 80% of the world’s terrestrial biodiversity, and they also form the source of livelihood for many different human settlements, including 60 million indigenous people.

Forests are some of the safest and comfortable homes for animals and birds. Many animals, birds can dwell peacefully in forests as it is a natural home for them.

They even find sufficient food for the day and together with their herds or groups. Forests are heaven for animals nowadays.

5. Minimise thepollution

It reduces air, sound and even thermal pollution. Forest have many plants and trees. The wind on the earth moves from one place to another. Similarly, the gas and air pollution diffuses to all over the air and get less severe. Presence of forest nearby helps these pollutants to be absorbed from the air.

6. Economic importance: Forest has a significant economic influence. Sometimes the economy of a region depends mostly on forests. Forests provide many natural resources which are of excellent value for money. For example, in the recent times, the red sandalwood from the jungles have been found to be of immense value, and the authorities are planning to capitalise the sale of the wood to run the government welfare schemes for the people. Similarly, in other countries, the presence of rainforests attracts a lot of tourists.

Some of the notable examples of reserves with economic importance are

1. Medicine:Many plant drugs like cinchona, cinnamon, eucalyptus, etc. are grown in the forest. Though smaller medicinal plants are grown by farming, drugs from large trees are available from forests alone. The medicines procured by this method are mostly, alkaloids, glycosides, tannins, etc. Besides one can also get essential oils.
2. Wood for Furniture: Forests are the sole reserve for best woods needed for furniture. There are many kinds of woods for different purposes like insect repellent ones (neem), red sandal, teak, etc. can be found in forests.
3. Honey: This is a sugary liquid produced by honey bees after consuming nectar from flowers. It is widely used in medicine, ice-creams, sweets and other confectionery. It is mostly obtained by cultivation using honey bees in controlled boxes. But honey from the wild forest has its taste and strength than the farmer made one.
4. Insect Wax: The insects which produce most wax are found in forests and the lac. When isolated this wax is used to make cosmetics and dye.
5. Good for Picnic and leisure:

Nowadays many forests are exploited as picnic spots. Though this may be disturbing to the native animals and people, still the governments encourage it for tourism revenue. There are various picnic and holiday packages offered to spend time in the midst of forests.

CAUSES OF DEFORESTATION

Deforestationis the removal of large areas of forest to providelandfor farming and roads, and to providetimber(wood) for building, furniture and fuel. Deforestation has a number ofundesirable effectson the environment. Deforestation and forest degradation can happen quickly, such as when a forest is clear-cut to make way for a palm oil plantation or a new settlement. It can also happen gradually as a result of ongoing forest degradation as temperatures rise due to climate change caused by human activity.

There are many causes of deforestation. Almost a half of the trees illegally removed from forests are used as fuel. Some other common reasons are:

• To make more land available for housing and urbanisation
• To harvest timber to create commercial items such as paper, furniture and homes
• To create ingredients that are highly prized consumer items, such as the oil from palm trees
• To create room for cattle ranching

Common methods of deforestation are burning trees and clear cutting. These tactics leave the land completely barren and are controversial practices.

In Zambia, deforestation is considered one of the priority environmental problems and woodland conversion to agriculture and wood harvesting for charcoal production seem to be the main causes of forest loss.

It is important to underscore that during the first half of the 20th century, traditional crop production in Zambia was dominated by shifting cultivation, the“citemene”system, which symbolised the effective use of tropical soil by the African indigenous peoples. For many years, the farmers of Zambia logged trees, burned the branches, and used ash as a fertiliser for the soil. Due to the nature of the soil, this method worked well and land could be used for 5 years before being left to rest.

However, there are a number of underlying causes related to the government’s economic liberalisation policies that have not been adequately investigated, forces that influence forest conversion to agriculture and clearance for charcoal production. These include:

• Higher price of electricity: The privatisation of electricity generation imposed on many countries by the IMF and the World Bank- increased electricity prices and affected the electrification policy, pushing local people to the use of charcoal as energy.
• Charcoal burning:The introduction of charcoal as an urban cooking energy source in Lusaka city created a new incentive among rural communities in central Zambia to clear woodlands to supply charcoal to the urban market.
• Removal of agricultural subsidies:Incomes from charcoal production were used to buy household requirements and in some cases these were invested in agricultural production after the removal of subsidies: a forest product had become a source of subsidy for agricultural production. Under traditional agricultural system trees were cut and burnt but with the commodification of charcoal, cut trees were converted to charcoal for sale and the land cultivated to produce both food and cash crops.
• Timber sales:Besides agriculture and charcoal production which are destroying the forest, uncontrolled or poorly controlled commercial exploitation of timber is a major cause of deforestation in Zambia’s Western, Eastern and Southern provinces. Few of the profits reaped from this activity, supported by the government, benefit the local communities, given that there are no timber industries worth talking about in those areas. All the money realised from timber sales goes abroad or ends in Lusaka.

In general deforestation is as result of the human economic activities and some natural causes which include the following:

• Conversion of forestsfor other land uses, including pulp, palm, and soy plantations, pastures, settlements, roads and infrastructure.
• Forest fires:Each year, fires burn millions of hectares of forest worldwide. Fires are a part of nature but degraded forests are particularly vulnerable. These include heavily logged rainforests, forests on peat soils, or where forest fires have been suppressed for years allowing unnatural accumulation of vegetation that makes the fire burn more intensely. The resulting loss has wide-reaching consequences on biodiversity, climate, and the economy.
• Illegal and unsustainable logging: Illegal logging occurs in all types of forests across all continents destroying nature and wildlife, taking away community livelihoods and distorting trade. Illegally harvested wood finds its way into major consumption markets outside the developing countries, which further fuels the cycle.
• Fuelwood harvesting: Over-harvesting for domestic use or for commercial trade in charcoal significantly damages forests.
• Mining: The impact of mining on tropical forests is growing due to rising demand and high mineral prices. Mining projects are often accompanied by major infrastructure construction, such as roads, railway lines and power stations, putting further pressure on forests and freshwater ecosystems.
• Climate change: Forest loss is both a cause and an effect of our changing climate. Climate change can damage forests, for instance by drying out tropical rainforests and increasing fire damage in boreal forests. Inside forests, climate change is already harming biodiversity, a threat that is likely to increase.

THE EFFECTS OF DEFORESTATION

Deforestation, as defined earlier, is the permanent destruction of forests in order to make the land available for other uses.

The removal of forests results into a number of undesirable effects which include the following:

• Reduction of habitats or food sources for animals, which can result in theirextinction.Animal and plant diversity is reduced, and food chains are disrupted.
• Loss of plant speciesand their genes which may be important for medical use or genetic engineering in the future.
• Removal of trees means there are no roots to hold soil, which can result insoil erosionand leaching of minerals. Desertification can eventually occur.
• Lack of roots and soil,floodingand mudslides. Lakes can become silted up.
• Leaching of nutrients into lakes and rivers leads to eutrophication.
• Less CO₂is absorbed from the atmosphere, more CO₂build up and increase thegreenhouse effect.
• Less O₂is produced and atmospheric O₂level can drop.
• Less transpiration and reduced rainfall.

1. Climate Imbalance:Deforestation also affects the climate in more than one ways. Trees release water vapour in the air, which is compromised on with the lack of trees. Trees also provide the required shade that keeps the soil moist. This leads to the imbalance in the atmospheric temperature further making conditions for the ecology difficult.Flora and faunaacross the world are accustomed to their habitat. This haphazard clearance of forests have forced several of these animals to shift from their native environment. Due to this several species are finding it difficult to survive or adapt to new habitats.
2. Increase in Global Warming:Trees play a major role in controlling global warming. The trees utilise the greenhouse gases, restoring the balance in the atmosphere. With constant deforestation the ratio of greenhouse gases in the atmosphere has increased, adding to our global warming woes.
3. Soil Erosion:Tree roots anchor the soil. Without trees, the soil is free to wash or blow away, which can lead to vegetation growth problems. Also due to the shade of trees the soil remains moist. With the clearance of tree cover, the soil is directly exposed to the sun, making it dry. After a clear cutting, cash crops like coffee, soy and palm oil are planted. Planting these types of trees can cause further soil erosion because their roots cannot hold onto the soil.
4. Floods:When it rains, trees absorb and store large amount of water with the help of their roots. When they are cut down, the flow of water is disrupted and leads to floods in some areas and droughts in other.
5. Wildlife Extinction:Seventy percent of the world’s plants and animals live in forests and are losing their habitats to deforestation. Due to massive felling down of trees, various species of animals are lost. They lose their habitat and forced to move to new location. Some of them are even pushed to extinction. It also has negative consequences for medicinal research and local populations who rely on the animals and plants in the forests for hunting and medicine. Our world has lost so many species of plants and animals in last couple of decades.
6. Water cycle: Trees are important to the water cycle. They absorb rain fall and produce water vapour that is released into the atmosphere. Trees also lessen the pollution in water, by stopping polluted runoff.
7. Life quality: Soil erosion can also lead to silt entering the lakes, streams and other water sources. This can decrease local water quality and contribute to poor health in populations in the area.

Forests are complex ecosystems that affect almost every species on the planet. When they are degraded, this can set off a devastating chain of events both locally and around the world. It is therefore more important that they are well safeguarded, and this made responsibility of each and everybody, everywhere.

MEASURES TO CONTROL DEFORESTATION

It has been a common belief that to counter deforestation, people simply need to plant more trees. Though a massive replanting effort would help to alleviate the problems deforestation caused, it would not solve them all. Reforestation would facilitate:

• Restoring the ecosystem services provided by forests including carbon storage, water cycling and wildlife habitat
• Reducing the build-up of carbon dioxide in the atmosphere
• Rebuilding wildlife habitats

In addition to reforestation, some other tactics are being taken to counteract or slow deforestation. Some of them include shifting the human population to a plant-based diet. This would lower the need for land to be cleared for raising livestock.

Global Forest Watch has also initiated a project to counteract deforestation through awareness. The organisation uses satellite technology, open data and crowdsourcing to detect and alert others of deforestation. Their online community is also encouraged to share their personal experiences and the negative effects of deforestation.

• The best solution to deforestation is to curb the felling of trees, by employing a series of rules and laws to govern it. Deforestation in the current scenario may have reduced however it would be too early to assume. The money-churner that forest resources can be, is tempting enough for deforestation to continue.
• Clear cutting of forests must be banned. This will curb total depletion of the forest cover. It is a practical solution and is very feasible.
• Land skinned of its tree cover for urban settlements should be urged to plant trees in the vicinity and replace the cut trees. Also the cutting must be replaced by planting young trees to replace the older ones that were cut. Trees are being planted under several initiatives every year, but they still don’t match the numbers of the ones we’ve already lost.

In Zambia, policies such as reducing emissions from deforestation and forest degradation (REDD+). To make this possible, some measures were taken, which include the following:

• Government has trained communities in alternative livelihood income-generating activities like the bee-keeping programme and other initiatives such as crafts, basket making and fruit propagation, aimed at reducing dependence on charcoal producing will be implemented by the Ministry of Lands, Natural Resources and Environmental Protection.
• Government has been conducting sensitisation activities on the importance of forestry and increase patrols as measures to protect reserves in different parts of the country.
• Government has intensified patrols on all major entry points within the reserve areas to curb the illegal trade in forestry products such as harvesting of logs, such as those of Mukula trees.
• In addition to that, the Government of Zambia, included in the 2015 budget the funds to renovate dilapidated forestry offices in various districts around the country.

Zambia instituted the Environmental Protection and Pollution Control Act in 1990. TheEnvironmental Council of Zambia(ECZ) was then established in June 1992 in the Ministry of Environment and Natural Resources. The ECZ is an institution charged with responsibility of implementing the environmental protection and pollution control Act of 1990. Since its inception theECZhas collected data on the environmental degradation and baseline data on pollution.

The raising of public, awareness is an important element in the promotion of environmental management, unless people are aware of the problems affecting them and consequent results, they would not be encouraged to take action in redressing the situation. The levels of awareness on the environment as well as environmental quality rights among Zambians is low. This is manifested in the widespread negative attitude that prevails among Zambians towards environment.

Although Zambia has no clear-cut environmental education policy, it is guided by education and environmental policies under the Ministry of Education, Environment and Natural Resources. Non-governmental Institutions are also involved in environmental education. Some of these includeWildlifeConservation Society(WCS), Zambia Environmental Education Programme (ZEEP), National Centre for Environmental Education (NCEE) and many others like Child to Child Programme for UNICEF; World Wildlife Fund (WWF)..

TheECZhas enacted a series of statutes aimed at protecting land, water, air and wildlife.

• TheECZhas formulations of standards and regulations onwater pollutionand effluent discharge, wastes management and waste water discharge and, pesticides and toxic substances unit.
• Noise abatement andair pollutioncontrol are in place, but regulations to back them are not yet finalised due to lack of expertise in the field. Environmental Impact Statements (EIS) have also been formulated, and wetlands policy documents on natural resources have been drafted
• Under the waste management theECZhas designated certain areas as dumping grounds.
• Strict rules have been set for companies and institutions to follow in waste disposal, failure to which they will be prosecuted. A governing licence to operate waste disposal site, the licence to transport waste shall be subject to conditions that will avoid spillage during transportation.
• Vehicles transporting the waste should be such that they do not scatter, pour or emit bad smells from the waste and should follow approved routes to licensed disposal sites or plant. One such disposal site has been designated in Kitwe at Uchi near the agricultural show grounds.
• A number of industries are taking measures to address the pollution problem. Many are attempting to change the technologies they are using to make them more environmental friendly with the regulation and standards set up by theECZ.

This change can be encouraged in Zambia if the law concerning environmental pollution was made stronger. At the moment the penalty of those companies and institutions polluting the environment is as low as K20.00.

Soil fertilityis defined as the ability of the soil to produce and sustain high crop yields indefinitely. In other words, fertility is a measure of the available nutrients in the soil and the proportion in which they occur. The soil is able to do this only if it can adequately supply the nutritional requirement of the crop plants in question.

A.Factors contributing towards soil fertility

Some of the factors are as listed below:

1. Soil depth- deep soils afford plant roots greater volume to exploit.
2. Good drainage to avoid water logging.
3. Good aeration to promote healthy root development and functioning.
4. High water-holding capacity
5. High level of nutrients
6. Soil pH.
7. Freedom from pests and diseases

In farming soil fertility may be lost in many ways. The common ways include the following:

1. Soil erosion by either water or wind
2. Soil capping: formation of an impervious layer of soil on the surface of the soil which obstructs rain infiltration leading to run off.
3. Development of hard pans short distance below the surface of the soil which impedes water percolation as well as root penetration. Hard pans may be caused by repeatedly ploughing at the same depth.
4. Loss of organic matter through rapid oxidation by soil micro-organisms due to unduly too frequent cultivations.
5. Leaching, especially serious with such nutrients as nitrogen which are highly soluble in water.
6. Loss of nutrients through sale of farm produce off the land without replenishing the nutrients removed in the produce.
7. Weeds. These compete for nutrients and moisture.
8. Alteration ofsoil pH, such as through misuse of certain fertilisers.
9. Build-up of soil pests and diseases by practicing certain systems of farming such as monoculture.

B.Plant Nutrients

In plant nutrients, you may discover that certain elements are essential for plant growth. Those being required in the largest quantity are known as major or macro elements while those needed in small amounts are known as minor or micro elements, and those needed in very minute quantities are known as trace.

The elements needed in large amounts are carbon, hydrogen and oxygen, obtained mainly from air and water. Nitrogen, Phosphorus, potassium, calcium, magnesium, sulphur and iron are obtained from the soil dissolved in water, or from application offoliar sprays. Essential trace elements are copper, manganese, zinc,molybdenum,boronand chlorine which can be made available to plants either through their roots or their leaves.

The table below summarises the importance of major and minor nutrients to the plants, deficiency symptoms and their sources.

Table 3.3

C.Inorganic fertilisers

As for Inorganic Fertilisers, these are artificially made fertilisers which are manufactured to supply the chemical nutrient needs of plants. The proportions of the main contents are stated on the container. Fertilisers which supply one main element such as nitrogen, phosphorus and potassium are known as straight fertilisers. Those containing mixtures in definite proportions are known as compound fertilisers.

The table below shows examples of straight fertilisers:

(a)Nitrogen

Phosphorus

(c).Potassium

It is necessary to note that top dressing fertiliser is sometimes applied with fertilisers of nitrogen. Plants, which are adequately supplied with potassium, are better able to withstand drought conditions than those suffering from a shortage.

On the other hand, Compound fertilisers are fertilisers containing more than two major elements along with minor elements. They are mostly applied as basal dressing fertilisers.

The table below shows the percentage constituents of Nitrogen, Phosphorus and potassium present in the different compound fertilisers

D.Organic Fertilisers

As for organics, these are the waste and residues of plants and animals. These organics can be in many forms such as poultry manure, cow dung/animal manures, farm yard manure, green manure and compost. They are natural manures and their decomposition is achieved by bacteria to form humus. Organic manures have bad and good effects on the soil.

Soil can either be acidic or alkaline depending on the parent material it was made from. The chemical composition affects the acidity or alkalinity of a soil, a factor which influences the availability of nutrients to plants. Soil acidity is also affected by the use of both natural andchemical fertilisers, lime and leaching.

SOIL pH REACTION

Soil pH is a measure of the acidity vs the alkalinity of the soil, and determines the capacity of that soil to exchange nutrients with plants growing in it. The soil acidity or alkalinity is influenced by the existence of hydrogen ions (H+) and hydroxyl ions (-OH). Therefore, soil pH is the degree of acidity or alkalinity of a soil.

If soil contains more hydrogen ions, it is said to be acidic. If more hydroxyl ions than hydrogen ions are present, the soil is alkaline. A soil with equal members of hydrogen ions and hydroxyl ions is neutral. Soil acidity or alkalinity is measured on a pH scale. The pH scale consists of a series of a number from 1 to 14.

As well as affecting the ability of plants to uptake nutrient by both chemical and biological processes, the pH also affects the diversity and species of soil microbiology. pH is usually measured on a scale of 1-14:

• A pH of 7 indicates neutral soil
• A pH above 7 indicates alkaline soil
• A pH below 7 indicates acidic soil

Soils with less than pH 7 are acidic and those with more than pH 7 are alkaline. This is as shown below

The degree of acidity or alkalinity on a pH scale is either 10 times more or less from one number to the next, depending on the direction on the pH scale.

1.Problems with high pH (alkaline) soils

Soil alkalinity is mainly caused by bicarbonates and carbonates, although phosphates,boratesand some organic molecules can contribute. In a soil with pH from 7 to 8.2, bicarbonates and carbonates of calcium and magnesium dominate.

Calcareous soils contain from 1 to 90 % lime material as calcium carbonates and these sparingly soluble salts cause the soil to have a pH of 8.0–8.2 which is not a severe problem for plant growth or agricultural production.

Problems are encountered in alkaline soils when sodium occurs or accumulates and forms salts such as sodium bicarbonate and sodium carbonate. These are highly soluble and increase the soil pH above 8.

When the pH is more than 9, the soils are considered highly alkaline and often have toxic amounts of bicarbonate, carbonate, aluminium and iron. Nutrient deficiency is also likely to be a major problem and the high amount of exchangeable sodium in these soils reduces soil physical fertility.

Most nutrients that plants need can be chemically assimilated when the pH of the soil solution ranges from 6.0 to 7.5.

• Below pH 6.0, some nutrients, such as nitrogen, phosphorus, and potassium, are less available.
• When pH exceeds 7.5, iron, manganese, and phosphorus are less available.

So getting your soil pH right is absolutely essential, if you want nutrient-dense vegetables.

Not all plants are the same – different crops prefer different levels of acidity – for example:

• Strawberries will yield well at a lower pH of 5.5 to 6.5
• Carrots love balanced soils pH of 6 to 7
• Sunflowers thrive in soils ph 7 to 7.5

So it depends on what you are growing as to what pH you want to nudge your soils towards. Keep in mind that most annual veggies prefer a bacterially dominated soil, which is leaning towards a pH of 7 – 7.5

Experiment: Testing the soil with a simple soil ph test kit:

Requirements: a soil pH test kit including the following:

We recommend the dye & powder system or Kelway Soil pH & Moisture Meter for broader areas.

• Use a small sample of soil, taken 10-15cm from the surface, and put on the mixing card
• Add a few drops of the indicator dye and dust with the white powder supplied with the kit.
• Wait about 30 seconds for the colour change to take effect. You will get a more accurate result if you wait a few minutes.
• Use the colour chart to match the colour of your soil samples. Each colour indicates what level pH your soil is.
• If in doubt, wait 2 minutes and check again the resulting colour
• Take several measurements in different spots in the garden. A minimum of six samples from different parts of the garden is a safe amount.
• A single reading may be an anomaly, so it is good to get an idea of the average pH in a plot. If they are all around the same, take the average and amend the soil accordingly. If one spot is very different than the rest, however, there is need to “spot treat” it.
• Record your results. You may need to reference your test results at a later date, as they may change over time.
• Test your soil annually to know exactly what your garden’s nutritional requirements are.

It is important to note that keeping a garden diary is a great way to improve garden and soil health for it is difficult to remember all the pH results just in one’s head

2.How to balance your soil’s pH

Once the soil is tested in at least six places and is found to be generally a pH of different from 7, the following measures should be taken:

If the soil is too acidic: less than 7 = low pH:

• Add green manure crops into your rotation with more frequency.
• Add organic matter in the form of a well-balanced, pH neutral compost, adding humus is the best way of changing pH.
• Add agricultural lime (not builders lime). As a rule of thumb, carefully apply 100g to each square metre.NOTElime can only be accurately applied if a total mineral test is performed. It will take a while to increase the pH this way , so you should see a change in the pH within 6 months. Be careful not to over apply.
• Add Dolomite , though it contains Magnesium, which if it is already present in large quantities, could block other minerals. Again, a total mineral test is a good idea before doing this.

If soil is too alkaline: greater than 7 = high pH:

• This soil will be harder to rebalance
• Add organic matter such as pine needles or decomposed tree leaves.
• Add green manure crops into your rotation with more frequency

• Add organic matter in the form of a well-balanced, pH neutral compost, adding humus is the best way of changing pH.

• In an extreme situation you could use powdered sulphur. Be very careful with this as sulphur is anti-microbial and will kill off the important microorganisms in the soil if applied regularly. Apply one handful per square metre, once a year. It works very slowly and the change in the pH may not easily noticed before about 6 months.

3.Significance of soil pH for plant growth

Some of the main effects of pH on plant growth are as follows:

Low pH lowers the availability of nutrients such as phosphorus and molybdenum. On the other hand, at alkaline pH above 8.5,” manganese, potassium, boron, iron and zinc become less available.

At very low pHs the concentration of available iron and aluminium in the soil solution may increase to such an extent as to become injurious or toxic to the plants.

Very acidic or low pHs inhibits the activity of soil microorganisms, notably the nitrifying and nitrogen-fixing bacteria.

Soil pH may affect the balance of the different microorganisms in the soil by influencing their competitive ability.

Plant damage by various soil pests e.g. nematodes is usually more serious in acid than in neutral soils. Different crop species react differently to pH.