FERTILISERS
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Fertilisers are concentrated sources of plant nutrients either in chemical (synthetic) or organic form which aim to promote plant growth and health. Synthetic fertilisers have significantly contributed to the creation of modern agriculture and are one factor in growth of global population, as crop yields have been able to increase therefore feeding more people. Synthetic fertilisers are also widely available for gardening to increase soil nutrients and improve the quality of the plants. Fertilisers can help plant growth; however, over-application of synthetic fertilisers can lead to them leaking into the environment and causing issues for local wildlife as plants begin to grow uncontrollably. Along with this, for synthetic fertilisers to be produced minerals have to be mined and manufactured causing many environmental issues in the process. There are many alternatives available, and examples can be found in the “Alternatives” section of this page
Synthetic Fertiliser
Pros:
– A synthetic fertiliser provides macro nutrients such as nitrogen, phosphorus, and potassium to the plant, which are needed to help growth (1).
– Areas with low quality soil fertilisers can help plants grow and even correct issues with soil deficiency (2).
– They are inexpensive and the exact ratio of nutrients can be seen on the packing so is easy to understand their effects (3).
– Their impacts can be seen in days as the nutrients is directly available to the plants (3).
Cons:
– Whilst synthetic fertilisers provide key macro nutrients to a plant, they often neglect other secondary nutrients like magnesium, which plants need too (1, 5).
– Inorganic, synthetic fertiliser products need to be manufactured, often their chemical are sourced from mines which can have significant negative effects on the local environment (4).
– Fertilisers can have such a high saturation of only the key three chemicals that it over-saturates the soil, blocking the plant from absorbing other key nutrients. Additionally, root burn can happen instantly from high mineral levels, as well as long term chemical use causing imbalance in the soils ph making it toxic (5).
– Over-application of fertiliser can lead to it being washed away, making its way into water systems, and becoming a pollutant, leading to unwanted growth such as algae blooms which can reduce oxygen levels in the water. Therefore pollution of fertilisers can cause negative effects on the whole ecosystem (5).
– Plants that grow bigger and lusher can attract more pests, impacting the plants. This may require action, see herbicides.
SYNTHETIC FERTILISER MINERALS
Plants need many different nutrients and vitamins to ensure healthy growth, however, they need three core macro nutrients Nitrogen, Phosphorus and Potassium. Synthetic fertilisers are used heavily in agriculture, but also gardening, to ensure the plants have the right amount of nutrients to successfully grow. However, the sourcing of the components needed for synthetic fertilisers can be problematic.
Phosphorus
Most phosphorus is obtained from mined phosphate rock. Mining has many consequences for the environment but also the resource itself, and there are many things to consider with phosphate rock:
– It is estimated that between 120- 170 million tonnes of the rock has been extracted each year for 30 years, with only 20-30 million tonnes of purified phosphorus being produced in a year (6). More than 85% of this goes into fertiliser (7).
– The resource is only located in a handful of countries, such as Jordan, America, Morocco, and Egypt, however some countries do have untapped resources (8). Due to this, the resources need to be transported, increasing the amount of carbon emissions generated in the whole production process of synthetic fertilisers.
– The volume of waste produced from phosphorus mining can vary with it ranging from 1-12 tonnes of waste extracted per 1 ton of phosphate ore (9).
– Phosphorus is a finite resource meaning that it will eventually run out one day, so can’t truly be a sustainable resource. Extraction needs to be reduced and made more efficient to reduce the damage to the environment and the levels of waste produced (10).
– The most common method of mining is open-cast mining, this causes large scale environmental disturbance and can destroy habitats, damaging the local ecosystem (11).
– Phosphorus mines also impact the surface water, with wastewater which may produce radioactive chemicals and dust contaminating water sources (12).
Nitrogen
The biggest elemental influence on plant cells and life, nitrogen is needed by plants in order to grow. The air contains large amounts of nitrogen, and processes exist which can extract nitrogen from the air by making ammonia, meaning that it does not need to be mined like Phosphorus or Potassium. However, there are issues associated with nitrogen as to much is being added to the environment unbalancing the natural system:
– Pollution of nitrogen into water systems can cause algae blooms which strip the areas of oxygen choking aquatic life , creating dead zones in oceans and rivers (13).
– Recent estimates of nitrogen efficiency suggest that only between 18-49% of nitrogen is used efficiently with the rest of it going to waste and polluting the environment (14, 15).
– Whilst garden usage will not have the same amount of damage as agriculture, nitrogen runoff from synthetic fertilisers could contribute to the degradation of the environment such as soil acidification. This is when nitrogen pulls key nutrients out of the soil making it to acidic meaning plants can’t take up nutrients properly (13).
Potassium
Potassium is used in fertilizers to ensure proper functioning and to enhance plants resistant to disease, insect attacks and temperature stresses (16). The biggest source of potassium worldwide is from potash salts which are mined. This mining has a large impact on the environment, however:
– The UK does have potash mines such as Boulby Mine on the northeast coast, meaning there are potential local sources for fertiliser. However, most of the world’s potash comes from Canada, along with Russia and Belarus (17, 18).
– Environmental degradation and a reduction of biodiversity is bound to occur from the nature of mining. Salinization of the land and freshwater ecosystems is a significant problem from the potash salts in waste products. Subsidence of the ground is another concern due to the underground mining methods (19).
– Solution mining involves pumping a heated brine solution into the deposits to dissolve potash salts then pumped out again. It’s a highly water intensive process and has high risk of water contamination especially if water sources are close like aquifers (20).
PEAT
Harvested and used in soil and compost for decades, peat is a surface layer of partially decomposed organic matter like plant material which has built up under wet and oxygen deficient conditions (21). Peatlands are rare environments only covering 3% of the worlds surface but hold 30% of carbon in soils and provides a habitat for a lot of wildlife (22). Peat has been widely used for decades, which has contributed to a lot of peat already being depleted, and harvesting still continues. This is problematic, however, due to the fact that peat is a massive CO2 store (helping reduce the impacts of enhanced climate change) whilst also providing habitats for organisms.
Pros:
– It is relatively cheap and widely available.
– Block cutting used to be the most common form of harvesting for peat, but new methods have been created, like vacuuming (23).
– Due to its water retaining abilities and abundance of organic matter, it makes a good compost and allows vegetation to grow (24).
– The UK harvests 700, 000 tonnes of peat each year, which means locally sourced peat will not have to travel as far and this will reduce its impact on the environment (24).
Cons:
– In the UK, peat is already a massively depleted resource, with at least 80% of the UK’s peatland habitats having been lost or damaged (22).
– Peat has massive environmental benefits, it is a major carbon sink with UK peatlands holding 3.2 billion tonnes of carbon (25).
– Peatlands are great natural flood protection and purification system. Peat is very good at absorbing water, being able to hold up to 20 times its weight and acting as a filter to clean water as it passes through (24, 26).
– A 5% loss of peatlands carbon would release the equivalent of the UK’s total annual greenhouse gas emission (24).
– Peatland deposits accumulate at around 1mm per year which is much slower than the rate they are being harvested making them not be a sustainable option (27).
– The UK imports around $46.5 million worth of peat annually with over 50% of it being imported from Ireland (28).
– Annually around 3 million cubic meters of peat are sold for gardening purposes in the UK, with around a 1/3 coming for peatlands found within the UK (29).
– Peat is still being used, despite its environmental issues, and ‘environmentally friendly’ and ‘organic’ labelling does not always mean peat free (30).
ALTERNATIVES: ORGANIC FERTILISERS
Organic fertilisers are derived from biological sources, such as manure or plant matter. They provide nutrients to soils and plants much like synthetic fertilisers, however, these are usually slower-acting and don’t always contain nitrogen, phosphorus, and potassium. The effectiveness of organic fertilisers is also limited seasonally. Both compost and organic fertilisers can be seen as more environmentally friendly than synthetic fertilisers, however, this is dependent on the type of fertiliser used.
Coir
Derived from coconut husks, coir is added to the soil to help encourage growth. It is rich in potassium and its pH is neutral creating a stable environment for cultivation.
– Coir is a by-product; coconut fruit and milk is taken away and the husk is waste. This gives a purpose to a waste product that would otherwise be thrown away. Despite this, coconuts are grown in hotter climates, such as that found in Sri Lanka and Mexico meaning the product will have to travel a fair distance to be used in the UK, adding to its carbon footprint as CO2 will most likely be emitted to transport the material (31).
– Coir has a fine texture along with moisture retaining properties but also allows proper drainage which helps prevents water logging and root rot (32).
– The structure of coir allows for great aeration in the soil as well as preventing compaction (33).
Seaweed/ Kelp
Seaweed is a natural plant that grows in abundance in the sea. It has been used and collected in the UK since Roman times and is used worldwide for food, soap, fertiliser etc. It can be a great source of nutrients for plants, but there are some things to consider when purchasing/ harvesting it:
– Production of seaweed has more than doubled in the last decade with 35 million tonnes being produced each year, with the sector continuing to expand. Asia is dominant in seaweed production, with China, Indonesia and the Philippines leading in volume of production (34).
– Seaweed harvesting can be sustainable, (it can grow 30-60cm a day ). However, it’s the management plans which are key as it’s an important habitat that helps coastal ecosystems thrive (35, 36).
– Companies have petitioned to harvest 0.15% of kelp in Scottish waters, around 34,000 tonnes. Sustainable measures were also taken into account, by leaving younger plants alone from the combs that harvest and giving areas time to recover from harvesting. However, the true extend of how sustainable seaweed production is in the UK is still unknown (36, 37).
– There are concerns about the harvesting of seaweed, as the machines remove entire plants, restricting the ability of a kelp forest to recover. There are also issues about the fact that removing seaweed can send ripples down the food chain, potentially causes negative impacts on biodiversity and genetic diversity (38).
– As a fertiliser seaweed contains nitrogen, potassium, phosphate and magnesium helping to add nutrients to the soil and support plant growth. It can be used in a variety of forms such as fresh, dried or processed , however they’re not true fertilisers as the nutrient content is guaranteed(39).
Manure
Manure is derived from animal dung and can be used from a variety of animals for nurturing the soil. It has been used as a fertiliser for centuries. Here are some things to consider with manure.
– The material is a good source of nitrogen. Along with this, organic nitrogen is more stable than synthetic (40, 41).
– The nutrients in manure enrich the soil, but it also conditions the soil, improving its quality and helping retain moisture. This reduces the need to use as much water as the soil will retain water much longer (40).
– Mixing manure with compost is one of the best ways to use it as a fertiliser as applying it directly can ‘burn’ the plants due to the large amounts of nutrients (40).
– Manure is great at improving soil quality and structure. It’s been shown to help reduce raindrop impact helping to decrease soil erosion (41).
– By using manure, a waste product is taken and repurposed. It also has further environmental benefits reducing the need for mined or manufactured chemicals (41).
– It is possible to buy manure from a farm or a stable, meaning the distance travelled can be reduced if purchased locally.
Bone Meal
Once used on a large scale, and even exported from the UK, bone meal is not used to the degree it once was but can still provide nutrients to soil. Here are some things to consider:
– Bone meal is made from ground animal bones and can be sourced as a byproduct of the meat industry. Whilst this reduces the waste from the meat industry, it does not stop the environmental impact of the meat industry (42).
– The bone meal is a great source of phosphorus which helps create strong roots, calcium which promotes sturdy growth and nitrogen that supports lush green foliage (43, 44).
– Slow release fertilizer, this means that it only needs to be applied once a year as it will slowly break down releasing the nutrients for the plants to feed on (43).
Bone meal may not be suitable for all soils, studies have found that phosphorus in organic fertilisers, such as bone meal, may only be available to plants in acidic soil with a ph of 7 or lower (43, 45).
Mushroom
Once used to grow mushrooms, this compost is left over and sold as a byproduct of the mushroom industry (46). Due to this, a waste product is recycled which is beneficial for the environment as it reduces the need for other fertilisers/composts. It is relatively cheap to buy and can be bought in bulk, however, it is usually alkaline and is not compatible with acidic plants (46). Its high salt content may also be problematic for some plants, but it increases the water retention in soil, which reduces the amount of water needed to water plants etc. as water will not escape as runoff as easily (47).
Eggshell
A common household waste item, these shells can be used to decompose in the soil, providing nutrients, notably calcium, to the soil. The shells alone cannot provide all the nutrients needed but do have some benefits for plants such as strengthening their cell walls (48). It also reduces the need for other forms of fertiliser, like synthetic chemicals or lime. As the shells take months to decompose, its recommended to crush them before tilling them into the soil and the best time to apply them in in the winter as it gives them time to break down for summer (49).
Used Coffee Grounds
Composting coffee grounds provides a source of nitrogen to plants and is slow acting in its nutrient release. The grounds will also attract wildlife, such as earthworms which are beneficial in improving soil quality. In reusing the coffee grounds, a waste product is given another purpose and stops it going into a landfill. However, coffee grounds are high in caffeine which in plants can actually restrict growth so they should be spread evenly to help not oversaturate an area (50).
