of
soil and fertilizer during a rain stormSynthetic fertilizers used in agriculture have
wide-reaching environmental consequences. According to the
Intergovernmental Panel on Climate Change (IPCC) Special Report on Climate Change and Land, production of these fertilizers and associated
land use practices are drivers of
global warming. The use of fertilizer has also led to a number of direct environmental consequences:
agricultural runoff which leads to downstream effects like
ocean dead zones and
waterway contamination,
soil microbiome degradation, and accumulation of
toxic compounds in ecosystems. Indirect environmental impacts include: N-crop-pest cascades, increased
greenhouse gas emissions and
environmental impacts of fracking for the
natural gas used in the
Haber process, the agricultural boom which is partially responsible for the rapid
growth in human population and large-scale industrial agricultural practices associated with it causing
pressure on biodiversity,
habitat destruction and
fragmentation, and agricultural
soil loss. In order to mitigate
environmental and
food security concerns, the
international community has included
food systems in
Sustainable Development Goal 2 which focuses on creating a
climate-friendly and
sustainable food production system. Most
policy and regulatory approaches to address these issues focus on pivoting
agricultural practices towards
sustainable or
regenerative agricultural practices: these use less
synthetic fertilizers (for example
sustainable agriculture), better
soil management (for example
no-till agriculture) and more
organic fertilizers (for example
organic farming,
conservation agriculture,
biodynamic agriculture). waste near
Fort Meade, Florida For each ton of
phosphoric acid produced by the processing of
phosphate rock, five tons of
waste are generated. This waste takes the form of impure, useless, radioactive solid called
phosphogypsum. Estimates range from 100,000,000 and 280,000,000 tons of phosphogypsum waste produced annually worldwide.
Water Phosphorus and nitrogen fertilizers can affect soil, surface water, and
groundwater snowmelt and can
leach into
groundwater over time. Agricultural
run-off is a major contributor to the
eutrophication of
freshwater bodies. For example, in the
US, about half of all the lakes surveyed by the
United States Environmental Protection Agency (US EPA) were
eutrophic in 2007 with a further alarming increase to 80 per cent in 2012. The main contributor to eutrophication is
phosphate, which is normally a
limiting nutrient, besides nitrogen; high P concentrations promote the growth of
cyanobacteria and
algae, the
demise of which consumes oxygen.
Cyanobacteria blooms ('
algal blooms') can also produce harmful
toxins that can accumulate in the
food chain, and can be harmful to humans. Fertilizer run-off can be reduced by using weather-optimized fertilization strategies. The resulting lack of dissolved oxygen greatly reduces the ability of these areas to sustain oceanic
fauna. The number of oceanic
dead zones near inhabited coastlines is increasing. As of 2006, the application of nitrogen fertilizer is being increasingly controlled in northwestern Europe and the United States. In cases where
eutrophication can be reversed, it may nevertheless take decades and need significant soil management before the accumulated nitrates in
groundwater can be broken down by natural
denitrification.
Nitrate pollution Only a fraction of the nitrogen-based fertilizers is converted to plant matter. The remainder accumulates in the soil or is lost as run-off. High application rates of nitrogen-containing fertilizers combined with the high
water solubility of nitrate leads to increased
runoff into
surface water as well as
leaching into
groundwater, thereby causing
groundwater pollution. The excessive use of nitrogen-containing fertilizers (be they synthetic or natural) is particularly damaging, as much of the nitrogen that is not taken up by plants is transformed into nitrate which is easily leached. Nitrate levels above 10 mg/L (10 ppm) in groundwater can cause '
blue baby syndrome' (acquired
methemoglobinemia). The nutrients, especially nitrates, in fertilizers can cause problems for natural habitats and for human health if they are washed off into
watercourses or leached through the soil into
groundwater. Run-off can lead to fertilizing
algal blooms that use up all the oxygen and leave huge "dead zones" behind where other fish and aquatic life can not live.
Soil Acidification Soil acidification refers to the process by which the
pH level of soil becomes more acidic over time. Soil pH is a measure of the soil's acidity or alkalinity and is determined on a scale from 0 to 14, with 7 being neutral. A pH value below 7 indicates
acidic soil, while a pH value above 7 indicates
alkaline or
basic soil. Soil acidification is a significant concern in agriculture and horticulture, leading to cation leaching, unstable soil aggregate structure, metal toxicity, decreased nutrient availability, and thus affecting soil biological properties and plant performances. Nitrogen-containing fertilizers release
ammonium or
nitrate ions, which can
acidify the soil as they undergo
biochemical reactions. When nitrogen-containing fertilizers, whether mineral or organic, are added to the soil, they increase the concentration of hydrogen ions (H+) in the soil solution, which lowers the pH of the soil. This may lead to decrease in
nutrient availability which may be offset by
liming. Soil acidification occurs also through
acid rain, a man-induced
concern despite severe measures to suppress or mitigate industrial
gas emissions since the 1970s. Among reported causes of acid rain, nitrogen fertilizers (whether mineral or organic), and the subsequent emissions of
nitrous and
nitric oxides are prominent in regions of intensive agriculture. The mechanisms are complex, involving
ammonia volatilization from manure (whether stored or spread) or urea and direct redeposition followed by
nitrification in the soil or previous oxidation to
nitrogen oxides in the atmosphere before redeposition as
nitric acid.
Accumulation of toxic elements Cadmium The concentration of
cadmium in phosphorus-containing fertilizers varies considerably and can be problematic. For example,
mono-ammonium phosphate fertilizer may have a cadmium content of as low as 0.14 mg/kg or as high as 50.9 mg/kg. The
phosphate rock used in their manufacture can contain as much as 188 mg/kg cadmium Examples are deposits on
Nauru and the
Christmas Islands. Continuous use of high-cadmium fertilizer can contaminate soils and
plants. Limits to the cadmium content of phosphate fertilizers have been considered by the
European Commission. Producers of phosphorus-containing fertilizers now select phosphate rock based on the cadmium content. Consequently, the widespread use of phosphate fertilizers has increased soil fluoride concentrations. Also of possible concern are the effects of fluoride on
soil microorganisms.
Radioactive elements The
radioactive content of the fertilizers varies considerably and depends both on their concentrations in the parent mineral and on the fertilizer production process.
Uranium-238 concentrations can range from 7 to 100 pCi/g (
picocuries per gram) in phosphate rock and from 1 to 67 pCi/g in phosphate fertilizers. Where high annual rates of phosphorus fertilizer are used, this can result in
uranium-238 concentrations in soils and
drainage waters that are several times greater than are normally present. However, the impact of these increases on the
risk to human health from radinuclide contamination of foods is very small (less than 0.05 m
Sv/y).
Other metals Steel industry wastes such as steel
slag are often recycled as a
soil amendment or for the production of fertilizers due to their high Ca and Mg content and various
trace elements necessary for plant growth. However, they can also include
toxic metals. Among them are
arsenic,
cadmium, and
nickel, while steel slag amendment rather contribute to immobilize
lead in the soil and thus to decrease its toxicity to the cultivated plant. The most common toxic elements in this type of fertilizer are
mercury, lead, and arsenic. Given the high cost of removing potentially harmful properties from steel slags, a better solution is to
immobilize them. The incorporation of
biochar to steel slag make even the mixture a good amendement for the (
passivation) of
heavy metals in agricultural soil. Highly pure fertilizers are widely available and perhaps best known as the highly water-soluble fertilizers containing blue dyes used around
households, such as
Miracle-Gro. These highly water-soluble fertilizers are used in the
plant nursery business and are available in larger packages at significantly less cost than
retail quantities. Some inexpensive retail granular garden fertilizers are made with high purity ingredients.
Trace mineral depletion Attention has been addressed to the decreasing concentrations of
micronutrients such as
iron,
zinc,
copper and
magnesium in many foods over the last 50–60 years.
Intensive farming practices, including the use of synthetic fertilizers, are frequently suggested as reasons for these declines and
organic farming is often suggested as a solution. much of the measured decline can be attributed to the use of progressively higher-yielding crop varieties that produce foods with lower mineral concentrations than their less-productive ancestors. It is, therefore, unlikely that
organic farming or reduced use of fertilizers (e.g.
conservation agriculture) will solve the problem; foods with high nutrient density are posited to be achieved using older, lower-yielding varieties or the development of new high-yield, nutrient-dense varieties. Fertilizers are, in fact, more likely to solve trace mineral deficiency problems than cause them: in Western Australia deficiencies of
zinc,
copper,
manganese,
iron and
molybdenum were identified as limiting the growth of
broad-acre crops and pastures in the 1940s and 1950s. Soils in Western Australia are very old, highly weathered and deficient in many of the major nutrients and trace elements. and zinc fertilizers are widely used to solve this problem.
Changes in soil biology High levels of fertilizer may cause the breakdown of the
symbiotic relationships between plant roots and
mycorrhizal fungi, in particular when in excess of plant requirements. It is still debated whether and how fertilizers affect
soil animals. Both organic and organic–mineral fertilizers increase the abundance of soil fauna whereas mineral fertilizers had no such effect, with
idiosyncratic responses of soil animal groups masking overall effects. Chemical fertilizers stimulates the growth of
microbial populations but did not change their richness and diversity, while decreases in
enzymatic activity have been registered. The combination of
soil acidification and high nitrogen content was probably unknown to most soil organisms before the advent of
industrial agriculture. More generally, soils are either acidic and nutrient-poor, or neutral to basic and nutrient-rich (nitrogen included), in relation to the pH-dependent capacity of
clay minerals to hold nutrients. This unexpected combination of excess nutrient availability and acid
stress causes a depletion in the sustainability of animal and microbial communities by weakening the linkages between aboveground and belowground components of
agroecosystems. Other
ecosystems are also affected by nitrogen-enriched acid rains originationg from intensive agricultural practices.
Sphagnum bogs are now shifting from
carbon sinks (thanks to the accumulation of recalcitrant sphagnum litter and
anoxic conditions) to carbon sources under the influence of nitrogen deposition and subsequent stimulation of
decomposer activity. Other nutrient-poor ecosystems are also strongly affected, such as
heathlands, with a surprising combination of higher
soil organic matter accumulation and higher
soil enzyme activity.
Organic agriculture Two types of agricultural management practices include
organic farming and
conventional agriculture. The former encourages
soil fertility using local resources to maximize efficiency. Organic agriculture avoids synthetic agrochemicals. Conventional agriculture uses all the components that organic agriculture does not use. The excess use of organic amendments (e.g. pig
slurry) may have detrimental effects on
water quality through contamination of the
aquifer and subsequent
eutrophication of the
water bodies it feds. This is a societal concern in areas where
pig farming conflicts with
environmental protection.
Fossil fuel consumption and sustainability Most synthetic fertilizer is fed from
fossil fuel, using fossil energy and
methane for producing
hydrogen used in the synthesis of ammonia by the
Haber process, as well as various
chemical reactions used in the synthesis of most fertilizers (e.g.
urea,
ammonium nitrate,
superphosphate). Some alternatives have been proposed for the production of hydrogen, such as
solar energy, waste treatment, or
electrolysis.
Contribution to the greenhouse effect concentrations (surface and atmospheric) for 2005; note distinct plumes The amount of
greenhouse gases
carbon dioxide,
methane and
nitrous oxide produced during the
manufacture and use of nitrogen fertilizer is estimated as around 5% of
anthropogenic greenhouse gas emissions. One third is produced during the production and two thirds during the use of fertilizers.
Nitrate is converted by
soil bacteria to
nitrous oxide, a
greenhouse gas. Nitrous oxide emissions by humans, most of which are from fertilizer, between 2007 and 2016 were estimated at 700 million tons of CO2 equivalent. Nitrogen fertilizer was used at a rate of about 110 million tons (of N) per year in 2012.
Nitrous oxide (N2O) is the third most important
greenhouse gas after
carbon dioxide and
methane. It has 296 times greater
greenhouse effect per ton than
carbon dioxide. The 2025 emissions contributed the equivalent of 700 megatons of CO2 to the atmosphere. It also contributes to
stratospheric ozone depletion. Altering processes and procedures could reduce these emissions.
Methane emissions from crop fields (notably rice
paddy fields) are increased by the application of ammonium-based fertilizers. These emissions contribute to global climate change as methane is a potent greenhouse gas. == Policy ==