Assessment of the nutrient composition, nutritional value, and environmental impacts of
fertilizer feedstock.
Ian Bobbitt
ENVS 190- Environmental Policy Thesis
5/18/2015
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Table of Contents
Abstract
3
Introduction
3
Animal Fertilizer
4
Raising Animals
4
Disease and Antibiotic Resistance
7
Runoff
9
Contamination of Drinking Water
10
Invasive Species
10
Nutritional Value
11
Processing
13
Synthetic Fertilizer
14
Nitrogen
14
Phosphate
16
Potassium
18
Nutritional Value
19
Processing
20
Conclusion
20
Tables and Figures
23
References
31
Abstract
Modern agriculture relies on large quantities of fertilizer to maintain crop production, but
producing and using this fertilizer can cause harm to the environment and human health. The two
types of fertilizer most commonly used are synthetic and animal waste fertilizers. This paper
highlights the causes and harmful effects associated with both types of fertilizer. Animal waste
fertilizer requires land, water and food for the animals, lowers biodiversity, pollutes waterways
and can lead to antibiotic resistance. Synthetic fertilizers require large amounts of energy to
extract and process, release heavy metals and other toxins into the environment and phosphate
rock is a limited resource that is rapidly being depleted. Agricultural yields are highest when
animal waste is used with synthetic fertilizers. Therefore improvements in technology, fertilizer
use and animal management are required to support the growing human population.
Introduction
Humans began intensive cultivation of crops during the Agricultural Revolution, around
8,000 years ago (Stein, 2010). This cultivation yielded more food per acre than hunting and
gathering, which allowed more people to live in an area; however, intensive agriculture had
many harmful effects on the ecosystem and soil.
Intensive crop cultivation depletes the vital nutrients and minerals that plants rely on to
grow. There are several agricultural practices that can alleviate this nutrient depletion, but the
most common and widespread practice is the application of fertilizer, which is rich in the
macronutrients nitrogen, phosphate and potassium, and also contains trace amounts of
micronutrients such as iron, manganese, and zinc (Combs et al., 1998).
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There are a few major sources of fertilizer, including animal waste, nitrogen in the air,
and nutrient rich ores. Extracting a usable product from these sources takes investment, in both
time and money. The costs of extracting fertilizer varies depending on the source of the fertilizer.
This paper will attempt to evaluate the benefits and the costs associated with using artificial
fertilizers and fertilizers derived from animal waste.
Animal Fertilizer
Raising Animals
Producing animal-based fertilizer is a resource intensive process due to the resource
requirements of raising the number of livestock necessary to produce large quantities of manure
and other waste (Mekonnen and Hoekstra 2012, Rasby, 2013, Sprinkle and Bailey, 2004,
Subcommittee on Beef Cattle Nutrition, 2000, N.R.C.S., 2015). There are two main ways to raise
livestock, based on how they are fed. The first is using grazing of rangelands or pasturelands to
provide the bulk of their food. Rangelands are uncultivated areas where livestock are allowed to
graze, whereas pasturelands are cultivated areas. Grazing area for livestock is the largest single
land use in the United States; around 27% of land in the 48 contiguous states is privately owned
rangeland and 6% is privately owned pastureland (N.R.C.S., 2014).
The second method of raising livestock is to raise them in confined areas. Raising
animals this way is defined as an animal feeding operation (AFO) and if the concentration of
animals is large enough, an AFO can be classified as a concentrated animal feeding operation
(CAFO) (N.R.C.S., 2015). If the site has more than 1,000 animal units on that site for more than
45 days out of the year, or if the animal manure from the site is released into a waterway, it is
classified as a CAFO. CAFOs are subject to EPA regulation due to the concentration and
potential harm of the animal waste generated on CAFOs. All AFOs rely on managing the
animals' food, waste and health in order to raise large numbers of livestock on small units of land
(N.R.C.S., 2015).
Animals grazing consumes food based on the size of the animals and the vegetation in the
area. In the United States the metric for measuring how much area an animal requires for grazing
is the animal unit month (AUM), and is defined as the amount of food required to support a
1,000 pound cow and her a calf for a month, which is around 800 lbs. of dry weight forage (Pratt
and Rasmussen, 2001). To convert the AUM to specific animal or species a conversion factor
called animal unit equivalence (AUE) needs to be used (Pratt and Rasmussen, 2001). Livestock
have different AUEs depending on the type of animal, developmental stage, and sex (Table 1).
Farmers and ranchers use AUMs and AUEs to estimate carrying capacities for specific
tracts of land. For example, an alfalfa pasture can support about 6 AUM per acre when used for
pasture grazing. This means that a farmer can support six head of cattle if each cow weighs 1,000
lbs., but if each cow weighed 1,200 lbs. then this pasture could only support five cattle. Using
uncultivated land for pasture grazing can typically support around three head of cattle (Hofstrand
and Edwards, 2013). In areas that receive little rainfall, or have vegetation that is not suitable to
forage, this number can drop so that ten acres are required to support one cow (Sprinkle and
Bailey, 2004).
AFOs are designed to raise more livestock on less land than can be supported by grazing
alone. AFOs have smaller pastures for livestock and require that a majority of the food for
livestock comes from harvested crops, typically grains. A non-dairy cow will consume 2% of
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their body weight in dry food each day, so a 1,000 lb. cow will consume about 20 lbs. of dry food
per day (Rasby, 2013). Using an alfalfa pasture to produce food for cattle can produce around 77.5 tons/acre, which can support twenty-four 1,000 lb. cattle per acre (Putnam et al., 2007).
These calculations give a general range of carrying capacities for cattle, from a tenth of a
head up to about twenty head of cattle per acre. Land requirements of other animals can be
calculated similarly. Evaluating the AUE of horses at 1.3 the range extends from a fifteenth to
about fifteen horses. Goats and sheep have an AUE of one fifth, so the carrying capacities are
around two acres per head up to forty goats/sheep per acre (Sprinkle and Bailey, 2004). Using
these carrying capacities, and estimating the amount of manure an animal can produce will give
an estimate of how much land it takes to produce a ton of manure. Estimating daily manure
production per animal unit shows that a highly productive alfalfa pasture used for grazing
(6 AUM/acre) can produce around 400 lbs. of animal waste when grazed by beef cattle. When a
highly productive alfalfa pasture is used to produce hay (24 AUM/acre) for beef cattle, about
1,500 lbs. of waste is generated (Penn State, 2015).
These estimates of fertilizer yield show that to produce any large quantity of animalbased fertilizer, large tracts of land must be set aside for raising livestock, but clearing land for
livestock will have tremendous impacts on the environment. For example, in Texas during 2012
there were over eleven million cattle spread over 150 thousand farms, and those farms laid claim
to about 90 million acres of permanent pastureland, not including pastured croplands or
woodlands (Census of Agriculture, 2012). These 90 million acres of permanent pastureland are
spaces where the native flora and fauna have been altered or displaced. This pattern is repeated
across the world, as large tracts of land are cleared for livestock.
Grazing intensity is another major impact that livestock have on native plants. Moderate
grazing, keeping around 1.3 tons of dry forage per acre intact, has been shown to have a dramatic
effect on the biodiversity of grasses and legumes found within a site. Intensive grazing reduces
overall biodiversity of plant life, whereas less intensive grazing, keeping 2 tons of dry forage per
acre intact, keeps biodiversity much higher (Scimone et al., 2007). Insect biodiversity also
suffers from intensive grazing, but less intensive grazing has been shown to increase insect
biodiversity (Wallis et al., 2007).
One major constraint of raising animals is the amount of water they require, both for
drinking and for sanitation. Water consumption depends on several factors such as ambient
temperature, diet, developmental stage, sex and weight (Table 2). In 2010 livestock withdrawals
from water sources were two billion gallons per day. This is just 0.02% of total water usage in
the United States (Maupin et al., 2010). Cattle consumption is higher than the water consumption
of other livestock animals (Tables 3 and 4). If the water required to produce food for these
animals is included, then these numbers increase. For example, it takes 1,799 gallons of water to
produce one pound of beef (Mekonnen and Hoekstra, 2012).
Disease and Antibiotic Resistance
When raising livestock in close quarters, diseases and infections can spread to other
animals more easily, due to the proximity of animals to each other and to sharing living space
with more animals (Hennessy, 2005). To combat this problem, farmers have used antibiotics and
other drugs to control the pathogens. Use of drugs has helped keep livestock disease-free, but by
using these drugs, the bacteria that cause disease are adapting to the drugs in a process known as
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antibiotic resistance. This is a problem because use and over-use of antibiotics will cause these
drugs to be less effective, and in the future possibly even useless (U.S.D.H.H.S., 2013).
The consequences of antibiotic use can extend beyond the animal and into its manure.
Antibiotics consumed by animals can be passed through their system and remain in their waste
(Bassil et al., 2013). If this waste were used as fertilizer, then the antibiotics could be taken up by
plants and stored within the edible parts. Antibiotic uptake by plants can be affected by the
concentration of antibiotics in the manure and by the size of the compound. Smaller compounds
were found in higher concentrations in plants, and larger compounds had smaller concentrations
(Bassil et al., 2013). The concentrations of antibiotics were no greater than consuming meat that
had been treated with antibiotics (Bassil et al., 2013).
Using manure from animals treated with antibiotics has a two-fold effect. It increases
antibiotic resistance in bacteria in the wild, but it also aids in spreading bacteria already resistant
to the antibiotic. One example of this occurred in China, where chicken manure produced by
chickens treated with antibiotics contained several strains of antibiotic resistant bacteria. When
this manure was applied as fertilizer to crops, specifically celery, pakchoi, and cucumber,
antibiotic resistant bacteria were found in higher concentrations, indicating a spread of resistant
bacteria (Yang et al., 2014). Unfortunately antibiotic resistance may persist after the use of
antibiotics has ceased. Pigs are routinely treated with antibiotics as piglets (Table 5), and even
after they have matured, bacteria can persist inside them that are resistant to the drugs (Heuer
and Smalla, 2007).
Runoff
The nutrients contained within manure can easily be washed away into nearby bodies of
water, leading to a problem known as runoff, which occurs when material gets washed away and
gets concentrated as it flows down the watershed. When runoff contains sediment from nutrient
rich fertilizer it can provide nutrients for aquatic plants, which can cause a growth spike in algae
and cause algal blooms. Algal blooms are massive growths of algae, and are a problem because
when the algae die bacteria began to break down the dead tissue. The bacteria use much of the
dissolved oxygen, which lowers the oxygen rate in the water to a level at which aquatic animals
can not survive. This loss of dissolved oxygen leads to a die off of aquatic animals and can create
dead zones; areas where nothing can live.
The Upper Mississippi River water basin has runoff from agriculture that occurs in the
region. This runoff is concentrated as streams and other tributaries bring more of the particles
into the main channel of the Mississippi River (Houser and Richardson, 2010). When the
Mississippi River empties into the Gulf of Mexico it creates the second largest dead zone in the
world. In 2001 the size of the dead zone was 20,700 km2 (Rabalais et al., 2002). However, due to
improving agricultural practices, and reducing nutrient sediment, the dead zone shrank to about
13,080 km2 in 2014 (U.S.E.P.A., 2014). Dead zones impact the local environment, but also local
industries such as fishing and tourism.
Runoff comes from both animal sources of manure and usage of manure as fertilizer.
Keeping large concentrations of livestock in one area causes a build up of manure, which can be
washed away into nearby bodies of water. Furthermore, improper storage of fertilizer can cause
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tremendous amounts of leaching and runoff. Greater distances from the a nearby bodies of water
also reduce runoff potential (Tittonell et al., 2010).
Contamination of Drinking Water
A problem that is similar to agricultural runoff is contamination of drinking water.
Manure can travel through the soil in a process known as leaching. When water comes into
contact with the manure, the water can dissolve the nutrients in the waste and carry them down
into the soil. Nitrate (NO3-) is the most susceptible to leaching because it is not absorbed by clays
or organic matter (Brandjes et. al, 1996). Soils act as a buffer for phosphate, which allows for
storage of phosphate, so the effects of phosphate leaching are minimized (Thomason, 2002). If
enough nitrate reaches the water table, it can contaminate the groundwater and make it
unsuitable for drinking. The EPA has set the maximum contaminant level (MCL) for nitrate in
drinking water at 10 mg of nitrate per liter of water (EPA, 2014). AFOs also can contaminate
groundwater with veterinary pharmaceuticals and steroidal hormones (Bartelt-Hunt et al., 2011).
Trace amounts of these compounds can pass through the animal and then leach out of the
manure.
Invasive Species
Most livestock is an invasive species that was deliberately introduced because these
animals provided food, transportation, or other goods and services. However, raising livestock
can stress the environment, such as when livestock introduce new pests and diseases, which can
displace or harm local wildlife (Pruvot et al., 2014). Livestock grazing can also change the local
flora that occur in the area (Milchunas et al., 1998). Rangeland biodiversity is decreasing as
natural rangelands are being converted into agricultural land (Haddad et al. 2015), and the mean
species abundance (MSA) of these systems is decreasing (Table 6) and will continue to decrease
(Alkemade et al., 2011). Human protection of livestock can also cause serious ecological harm,
such as in the midwestern United States where wolves and coyotes were hunted to extinction in
some areas (N.P.S., 2015).
Nutritional Value of Fertilizer
There are two types of nutrients in fertilizer. The first type is macronutrients.
Macronutrients are the chemicals and compounds that an organism needs in large quantities. For
plants there are four primary macronutrients, carbon, nitrogen, phosphate, and potassium, and
three secondary macronutrients, calcium, magnesium and sulfur (Whiting et al., 2014). Carbon
dioxide is readily found in the air and taken into the plant to be used in photosynthesis, but the
rest of the macronutrients must come from soil.
While plants require relatively large amounts of macronutrients, the ratio of those nutrient
requirements varies from plant to plant. For example sorghum requires an
nitrogen:phosphate:potassium (NPK) ratio of 100:21.8:18.2, whereas wheat requires an NPK
ratio of 120:26.2:50. Legumes also require different ratios, with plants like cowpea having a ratio
of 32:5:60 and mungbean with a ratio of 30:4:36 (Sarker et al., 2011).
The variety of nutrient requirements means that no single source of fertilizer will be the
best in all situations, so it is best to evaluate a variety of fertilizers and look at the specific ratios
found within. Cattle manure has a typical nutrient ratio of 10:3:6, but it can vary depending on
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how the cow is being raised and the types of feed it receives. Swine manure has a ratio of about
13:7:4. Poultry manure tends to be around 22:15:15. Horse manure is close to 4:2:3 and sheep
manure yields 20:22:23 (Sawyer, 2009). These nutrients ratios of manure do not match up with
the nutrient requirements of most plants. This usually leads to people overusing manure to ensure
that plants get an appropriate amount of nutrients, and can result in lower crop yields and
decreased nutrient uptake.
Secondary macronutrients, calcium, magnesium, and sulfur, and micronutrients, boron,
chlorine, copper, iron, manganese, molybdenum and zinc, are also contained within animal
manure (Table 7), but their inclusion in fertilizer tends to have a different effect on soil fertility
than the primary macronutrients. Applying manure can increase the concentrations of these
nutrients several times over, increasing the salt content of the soil as well as affecting the pH.
This can cause issues with plants as they uptake these elements, as well as affect mineral runoff
and soil fertility (Brouwer et al., 1985).
Comparing several treatments of farm animal waste to varying levels of nutrients in
synthetic fertilizer showed that using farm animal waste improved soil quality, but the best
results were obtained when farm animal manure was used in tandem with a synthetic supplement
(Sharma et al., 2014). The okra plant also grew best with the mixed application of bioslurry, a
watery mixture of manure and nitrogen fertilizer, as opposed to synthetic nitrogen fertilizer alone
(Shahbaz et al., 2014). Soil amendments made of a mixture of animal waste and synthetic
fertilizer can match the nutrient requirements of plants better than animal manure alone, yielding
greater plant growth.
Processing
The length of time that manure is in storage affects its nutritional quality. During the
initial few months of storage nutrient loss is relatively high, but the loss decreases as the manure
dries out. This can result in at least half of all macronutrients being removed from the fertilizer
(Figures 1,2,3,4). Therefore it is important to use manure before the nutrients are lost; however,
untreated animal manure can contain pathogens and pests, which can harm plants and crops.
To remove these harmful side effects, the manure must be processed or treated. Balancing
nutrient retention and processing is important to utilizing fertilizer. Ways to process fertilizer
vary, and they can be as simple as drying out the manure or as complex as treating the manure
with chemicals (Black, 1967).
The most common method of storage is to use a “lagoon” where the manure is stored in a
pond or swamp-like area while the waste breaks down. This method is the easiest to implement,
but it can release organic sediment into groundwater, release odors and sediment into the air and
has a deleterious effect on local flora and fauna (Black, 1967).
The least expensive way of treating manure is to store it in tanks or dry it out in piles
before being used on agricultural land. This method has drawbacks in that it requires adequate
storage for about 6 months of animal waste, requires nearby agricultural lands and, if improperly
managed, odors can escape or organic solids can percolate into groundwater (Black, 1967).
Composting is another treatment method that is fairly cheap. This method treats the
manure by storing it until bacteria and fungi break down the waste. The problem with this
method is that most manure is too low in carbon to have complete breakdown, since composting
requires at least a 20:1 carbon to nitrogen ratio, and most manures are close to 10:1 (Black,
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1967). Mixing plant material with the manure can help the breakdown process. Mixing sawdust
in with swine manure at a 4:1 manure to sawdust ratio created higher quality compost than swine
manure alone (Troy et al., 2012).
The amount of animal waste generated makes treating waste chemically impractical,
since the costs of chemicals and infrastructure required are prohibitive. Large-scale,centralized
processing plants tend to be too expensive to operate and maintain, and small-scale farm
operations tend to be too complex for most farmers to operate (Melse and Timmerman, 2009).
Synthetic Fertilizer
Synthetic fertilizer is created by extracting minerals out of the earth or from the air and
then refining them into a form that is readily usable by plants. Creating synthetic fertilizer is
extremely resource intensive, requiring large amounts of energy to collect and process the
minerals. The most common way of acquiring these minerals is by mining them out of the earth,
but there have been attempts to create fertilizer from other sources. To examine synthetic
fertilizer, each primary macronutrient (nitrogen, phosphate and potassium) will be analyzed in
terms of mining, extraction, and processing.
Nitrogen
Nitrogen makes up around 75-79% of the atmosphere of the earth but it is in a form that
plants cannot readily use. Nitrogen in the air is comprised of N2, but most plants require that
nitrogen be part of a nitrate compound (NO3-) or the ammonium compound (NH4+) so this
nitrogen needs to be converted (Mattson et al., 2009).
There are several natural processes and organisms that perform this conversion, and the
primary way that nitrogen gets added to soil is by nitrogen-fixing bacteria (Nagatani et al., 1971).
The capability of bacteria to fix nitrogen into the ground sets a limit to the amount of nitrogen
that can be added to soils, or converted into useful compounds. However, until the late 19th
century the process by which nitrogen is added to the soil was not well known; it was only
known that using legumes helped improve soil fertility. In 1888 the prokaryotes responsible for
fixing nitrogen were discovered (Hirsch, 2009).
At the same time scientists had tried to use chemicals and energy to convert the nitrogen
from the air into a usable form. In 1910, this culminated in the Haber-Bosch process, which
converts nitrogen in the air into ammonia, using high temperatures, high pressure and in the
presence of a catalyst. Hydrogen is added to the process by combusting methane, but it was
originally created using electrolysis of water (Aftalion, 2001).
This process has several negative impacts. The largest one is the amount of energy
required to generate ammonia. It takes about 30 million BTUs to create a ton of ammonia, which
is about 300-400 times more energy than used to produce phosphate or potassium oxide. This
energy usage causes large quantities of CO2 to be added to the atmosphere. In 2006 the United
States emitted 14.6 million metric tons of CO2 due to the production of ammonia (U.S.E.P.A.,
2009). It was estimated that for every ton of nitrogen produced, about 7.8 tons of CO2 is
produced. If the best available technology was adopted then this number would drop to about 3.6
tons (Fossum, 2014). China has high CO2 emissions, at around 8.3 tons of CO2 emitted per ton of
nitrogen. Improving coal heat exchange operations in plants, increasing the efficiency of the
Haber-Bosch process so that more nitrogen is collected per gigajoule and upgrading older
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facilities to more modern plant standards will greatly decrease CO2 emissions to about 5.8 tons
of CO2 per ton of nitrogen (Zhang et al., 2013).
Phosphate
Phosphate mining, which provides a necessary nutrient for synthetic fertilizer, helped fuel
the Green Revolution because it allowed phosphate to be extracted and processed, whereas prior
to industrial mining most plants took in ambient phosphate from the environment. Most
phosphorous mining operations occur in South America, the Pacific Islands, Africa, China, the
Middle East, Russia, and the United States (Table 9). In 2013 world production of phosphate
rock was 225 million tons (Jasinski, 2015). In 1997 the US phosphate mining industry used
around 15.2 trillion BTUs to produce around 50.6 million tons of phosphate (U.S.D.E.
Phosphate, 2015). This number is expected to increase as readily exploitable deposits are
depleted.
An important concept in mining is the idea of peak supply. The basis of this concept is
that there are a finite amount of any specific resource, and the easiest deposits of this resource
are exploited first. Thus there will be a point where production starts to fall as deposits become
harder to exploit. World phosphate deposits are estimated at 300 billion tons, but only 67 billion
tons are economically profitable to exploit (Jasinski, 2015). It is estimated that peak production
of phosphate rock will be reached in 2040 and decline afterward, but demand will continue to
rise (Schroder et al., 2009).
Mining for phosphate mixes water with the phosphate matrix (a mix of clay, pebbles and
phosphate rock) to create a slurry, which is then separated. Pebbles and larger sediment are
removed with a conveyor belt while the smaller phosphate particles and sand must go through
more intense separation. The remaining mixture, mostly clays and water, is sent to lie in ponds
which allow for much of the sediment to settle along the bottom. This water can then be reused
in the process. If this water contains concentrations of toxins higher than the EPA maximum
contaminant level, then the water must be treated to remove the excess contaminants. The most
common contaminant is phosphate, and to remove it from the water a lime slurry (Ca(OH)2) is
used (U.S.D.E. Phosphate, 2015).
Phosphate is primarily mined using surface mining techniques, which requires the
removal and storage of the excess soil and bedrock called waste material. This waste material is
stored in tailings piles, either for reclamation or for dam construction. However, the waste
material often contains harmful contaminants, such as heavy metals, which can harm the local
environment (U.S.D.E. Phosphate, 2015).
Tailings piles tend to have a higher concentration of heavy metals than what is found at
ground level. Many of the heavy metals, such as arsenic, selenium, chromium, and lead, are
toxic. These heavy metals can be released into the environment via wind or leaching and can
cause severe harm to plants and wildlife. For example, selenium toxicity has been linked with
congenital defects in waterfowl (Torres-Vega et al., 2012). Lead impairs the nervous system,
liver, kidneys and can even cause death (U.S.D.H.H.S., 2007). If the concentrations of these
heavy metals get too high they can contaminate large bodies of water, especially sources of
drinking water. The EPA has strict regulations about the levels of contaminants that can be in
public drinking water, due to potential harm of ingesting these contaminants (Table 10).
Phosphate mining can also release radioactive material into the environment, since
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phosphate deposits usually have significant quantities of uranium nearby (U.S.E.P.A., 2014). The
radioactivity of uranium complicates mining and storage of the waste material, because if this
material were to be released into the environment it could cause harm to wildlife and people.
According to the EPA, mining in Florida for phosphate ores produces phosphogypsum, a calcium
sulfate byproduct, that has “ten times the background levels in soil for uranium and sixty times
the background levels in soil for radium-226” (U.S.E.P.A., 2012).
Potassium
The USGS estimates that there is about 7 billion tons of potash in deposits in the US, and
globally there are 250 billion tons. There are only a handful of countries that have sufficient
deposits of potash ore (Table 7). In 1979 an estimated 4.2 million BTUs were required to
produce a ton of potassium oxide (U.S.D.E. Potassium, 2000).
There are three primary methods for mining potassium from potash. Conventional mining
uses drills, explosives, and other heavy machinery to extract the ore from the rock face (U.S.D.E.
Potassium, 2015). Conventional mining makes up 80% of global potash production
(PotashCorp, 2013).
Solution mining uses a brine or a salt water solution to dissolve potassium contained
within the rock face. It is then pumped out into an evaporation pond, and the water is recycled to
be used again. The sediment is then removed from the bottom of these ponds (U.S.D.E.
Potassium, 2015). This method can cause severe water quality issues if the brine is not disposed
of properly. The largest potassium mine in Russia, the Upper Kama Potash-Magnesium Salt
Deposit, has had severe problems with disposal of its excess brine. Programs are underway to
offset the cost, such as finding optimum times to discharge waste and develop better distribution
patterns to spread the impact (Lepikhin et al., 2012).
The final major method is cut-and-fill stope mining. This method creates stopes, open
sections in the bedrock requiring no artificial support, and is similar to conventional mining, but
the waste rock generated is used to create a new platform for mining the rock face. This allows
for more efficient mining and extraction of potash ores (U.S.D.E. Potassium, 2000).
Potassium mining faces many of the same problems that phosphate mining does. Potash
waste material has a higher concentration of heavy metals than ground-level soils. Extraction of
potash ore and the waste material can release heavy metals into the environment, which can harm
wildlife or foul water sources. Sediments released by mining can clog rivers and lake beds.
Nutritional Value
The ratio of nutrients in synthetic fertilizer is easier to manipulate than in manure-based
fertilizer since the amount of nutrients added to the mixture can be controlled. This allows
synthetic fertilizer to contain a single nutrient, such as nitrogen fertilizers, or be specialized for a
specific crop. For example, wheat, sorghum, cowpea and mungbean have suggested NPK ratios
of 120:26.2:50, 100:21.8:18.2, 32:5:60, and 30:4:36 for maximum growth, and fertilizers can be
designed to contain appropriate amounts of nutrient for each crop (Sarker et al., 2011).
Even with nutrient ratios targeted for specific plants, crop yields tend to do better when
there is a mix of animal manure and balanced fertilizer (Sharma et al., 2014). Phosphate is
beneficial to plant growth as a soil supplement. Comparing compost enriched with rice straw and
phosphate rock to unenriched compost, biological activity was highest in the enriched compost.
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Furthermore, a mixture of fertilizer and enriched compost yielded richer soils and soil fertility
(Meena and Biswas, 2014).
Processing
One major drawback of producing synthetic fertilizer is the amount of energy it takes to
turn the feedstock into fertilizer. The global average of energy consumption is about 32.5 million
BTUs per ton of ammonia (Kelischek, 2011). Phosphate takes much less energy, requiring
around 1,070 BTUs per ton of material produced (U.S.D.E. Phosphate, 2015). Potash processing
requires around 44,400 BTUs, most of it used to operate a rod mill to crush the ore (U.S.D.E.
Potassium, 2015). Combining these costs of production with the costs of extraction yields 30
million BTUs per ton of ammonia, 70,670 BTUs per ton of phosphate and 88,900 BTUs per ton
of potash.
Conclusion
Fertilizer created an agricultural boom and spurred human population growth, but using
fertilizer has drawbacks, which vary depending on the source of the fertilizer. Using fertilizer
derived from animal waste require land, water and food be set aside to raise livestock. Livestock
also cause significant harm to the environment by displacing native species or contaminating
groundwater. Furthermore, using manure from animals that have been treated with antibiotics
can encourage antibiotic resistance in bacteria.
Many of these costs can be offset. Improving livestock diet will limit the amount of
resources that are required to raise these animals (Abberton et al., 2008; Arthur and Herd, 2005;
Kolver and Muller, 1998). Environmentally friendly farm planning can minimize the
fragmentation and displacement of native species (Annetts and Audsley, 2002; Smithers and
Furman, 2003). Improving manure management and treatment can limit the amount of runoff and
leaching that occurs (Lichtenberg and Penn, 2000; Oenema et al., 1998). Using antibiotics less
frequently will help prevent bacterial resistance (Mathew et al., 2007).
Synthetic fertilizer has several drawbacks as well. Producing synthetic fertilizer requires
large amounts of energy, with nitrogen being the most energy intensive nutrient to produce.
Phosphate and potassium mining can cause heavy metals and other toxins contained in the
extracted material to leach out into the environment, which harms plants and wildlife, and
contaminate ground and surface water. Phosphate rock is a limited resource which is being
consumed rapidly with no long term resource management strategy.
These costs can be offset as well. Using renewable sources of energy, removing old
technology and replacing it with newer can lower the carbon footprint of extracting and
processing these nutrients (Lund and Mathiesen, 2009; Worrell and Blok, 1994; Zhang et al.,
2013). Contaminant release can be limited by proper storage of waste material and improving
treatment options (Hilson and Murck, 2001; Lepikhin et al., 2012). Phosphate can be used more
efficiently and can also be managed so that the world's current reserves can last for a longer
period (Jasinski, 2015).
If these changes are implemented, then the environmental impact of agriculture can be
shrunk dramatically. Both animal based fertilizer and synthetic fertilizer are necessary, as crops
have the highest yield when both types of fertilizer are used in conjunction with each other
21/37
(Meena and Biswas, 2014, Sharma et al., 2014). As humanity's population keeps growing it is
important to maximize these agricultural benefits while minimizing the ecological detriments.
Tables and Figures
Table 1: A list of animal unit equivalence, used to
determine how much food animals consume (Pratt
and Rasmussen, 2001)
Animal Unit Equivalence
CLASS OF ANIMAL
Cow, 1000 lb, dry
Cow, 1000 lb, with calf
Bull, mature
Cattle, 1 year old
Cattle, 2 years old
Horse, mature
Sheep, mature
Lamb, 1 year old
Goat, mature
Kid, 1 year old
Deer, white tailed, mature
Deer, mule, mature
Elk, mature
Antelope, mature
Bison, mature
Sheep, bighorn, mature
ANIMAL UNIT EQUIVALENT
0.92
1
1.35
0.6
0.8
1.25
0.2
0.15
0.15
0.1
0.15
0.2
0.6
0.2
1
0.2
23/37
Table 2: Daily water intake for cattle based upon several factors such as class, weight and ambient temperature
(Subcommittee on Beef Cattle Nutrition, 2000)
Approximate Total Daily Water Intake of Beef Cattle
Temperature in °F (°C)
Weight
40
(4.4)
50
(10)
kg
lb
liters
gallons liters
gallons
182
273
364
400
600
800
15.1
20.1
23
4
5.3
6.3
16.3
22
25.7
4.3
5.8
6.8
273
364
454
600
800
1000
22.7
27.6
32.9
6
7.3
8.7
24.6
29.9
35.6
6.5
7.9
9.4
409
500
900
1100
25.4
22.7
6.7
6
27.3
24.6
7.2
6.5
409
900
43.1
11.4
47.7
12.6
636
727
1400
1600
30.3
32.9
8
8.7
32.6
35.6
8.6
9.4
60
(21.1)
70
(21.1)
80
liters
gallons liters
gallons liters
Growing heifers, steers and bulls
18.9
5
22
5.8
25.4
25
6.6
29.5
7.8
33.7
29.9
7.9
34.8
9.2
40.1
Finishing cattle
28
7.4
32.9
8.7
37.9
34.4
9.1
40.5
10.7
46.6
40.9
10.8
47.7
12.6
54.9
Wintering pregnant cows
31.4
8.3
36.7
9.7
28
7.4
32.9
8.7
Lactating cows
54.9
14.5
64
16.9
67.8
Mature bulls
37.5
9.9
44.3
11.7
50.7
40.9
10.8
47.7
12.6
54.9
(26.6)
90
gallons liters
(32.2)
gallons
6.7
8.9
10.6
36
48.1
56.8
9.5
12.7
15
10
12
14.5
56.1
65.9
78
14.3
17.4
20.6
-
-
-
17.9
61.3
16.2
13.4
14.5
71.9
78
19
20.6
Table 3: Water requirements for livestock based upon class and weight
(Ward and McKague, 2007)
Swine
Weaner
Feeder pig
Gestating Sow/Boar
Lactating sow
Horse
Small
Medium
Large
Sheep
Feeder lamb
Gestating meat
ewe/ram
Lactating meat ewe
plus unweaned
offspring
Gestating dairy
ewe/ram
Lactating dairy ewe
Weight Range
(kg)
7-22
23-36
36-70
70-110
-
Water Requirement Range
(L/day)
1.0-3.2
3.2-4.5
4.5-7.3
7.3-10
13.6-17.2
18.1-22.7
Average Typical Water Use
(L/day)
2
4.5
4.5
9
15
20
226
453
680
13-20
26-39
39-59
16.5
32.5
49
27-50
3.6-5.2
4.4
80
4.0-6.5
5.25
80
9.0-10.5
10
90
90
4.4-7.1
9.4-11.4
5.75
10.4
Table 4: Water requirements for chickens based on weight and type
(Ward and McKague, 2007)
Chicken Type
Laying hens
Pullets
Broiler breeders
Weight Range
(kg)
1.6-1.9
0.05-1.5
3.0-3.5
Water Requirement Range
(L/1,000 birds/day)
180-320
30-180
180-320
Average Typical Water Use
(L/1,000 birds/day)
250
105
250
25/37
Table 5: Variety of antibiotics given to pigs to treat specific diseases
(Muirhead et al., 1997)
Table 6: Rangeland description and the mean species abundance (MSA) with standard error (SE)
(Alkemade et al., 2010)
Rangeland Species Abundance
Natural rangelands
Moderately used rangelands
Intensively used rangelands
Man-made grasslands
Ungrazed abandoned rangelands
Short description
MSA
Rangeland ecosystems determined by
climatic and geographical circumstances
and grazed by wildlife or domestic animals
at rates similar to those of free-roaming
wildlife
Rangelands with higher stocking rates:
grazing has different seasonal patterns or
vegetation structure is different compared
with natural rangelands
Rangelands with very high stocking rates:
grazing has different seasonal patterns and
vegetation structure is different compared
with natural rangelands
Rangeland with high degree of human
management, including converted forests
Original grasslands no longer in use,
lacking wildlife grazing and no forests
developed
SE
1—
0.6
0.04
0.5
0.06
0.3
0.08
0.7
0.07
Table 7: Average nutrient concentrations of livestock manure (Combs et al., 1998)
8.4
1.5
13.5
5.5
4.7
1.5
9.8
2.4
2.8
1.6
10.4
1.2
6.2
6.9
51.8
2.5
2.6
2.6
17.6
0.8
0.9
0.2
1.4
0.6
Total Concentration (wet weight basis)
Al
Na
Zn
B
Mn
Cu
Se
Co
Cr
As
lbs/ton wet ton
0.5
0.5
0.2 0.03 0.01 0.06 0.01 0.0002 0.0003
0.001 0.0001
0.5
0.5
0.2 0.03
0 0.04 0.01 0.0001 0.0003
0.001 0.0001
3.1
2.4
1.1 0.17 0.03 0.19 0.08 0.0009
0.002
0.005 0.0001
0.1
0.1
0.1 0.01 0.01 0.02
0 0.0001 0.0001 0.0001 0.0005
24
4.2
27.6
17
47.6
12
60.2
31.5
29.2
5.9
36.6
23.2
26.5
7.1
33.9
17.2
6.6
1.2
7.5
4.8
5.3
1.2
6.8
3.9
19
4.1
23.9
14.7
14.4
2.2
16.3
11.3
59.9
18.1
94.8
22.6
55.9
17.9
90.4
21.6
39.2
11.2
55.4
14.5
64.8
11.2
191.9
23.9
7.6
1.9
10.6
3.7
7.5
2.3
10.7
2.7
3
4.3
21.8
0.5
2.6
3
12.7
0.4
27.3
10.3
50.2
11.1
10.5
4.7
19.6
3.4
21.1
10.5
39.8
6.8
15.1
8.8
36.8
5.2
5.3
3
14.7
1.9
2.2
1
3.9
0.8
0.9
0.7
3.4
0.2
0.7
0.6
3
0.2
69.4
19.1
95.9
42.1
36.8
15.6
63.3
25.2
25.1
12.2
41.8
8.3
21.8
9.9
35.6
12.7
7.4
3.1
10.7
4.1
5.3
1.5
6.7
3.9
2.5
2.8
7.4
0.7
2.4
3.6
8.7
0.4
N
Dairy solid
average
sd
max
min
Swine solid
average
sd
max
min
Poultry all
average
sd
max
min
Dairy liquid
average
sd
max
min
Swine liquid
average
sd
max
min
P2O5
K2O
Ca
Mg
S
Fe
6.7
1.5
8.6
5.3
0.79
0.21
1.02
0.53
0.04
0.01
0.05
0.03
1.09
0.12
1.3
0.99
0.5
0.18
0.72
0.33
0.002
0.001
0.003
0.002
0.003
0.001
0.005
0.002
0.01
0.002
0.013
0.008
0.0024
0.0009
0.0039
0.0016
7.8 0.48
3 0.17
12.3 0.83
1.7 0.17
lbs/1000 gal
3.3 0.11
1.8 0.06
7.7 0.23
0.6 0.02
0.08
0.05
0.3
0.02
0.61
0.27
1.13
0.15
0.66
0.39
1.34
0.02
0.002
0.001
0.004
0.001
0.003
0.001
0.005
0.001
0.014
0.009
0.033
0.001
0.033
0.051
0.173
0.0002
0.03
0.02
0.06
0.01
0.11
0.05
0.2
0.03
0.12
0.24
1.19
0.01
0.001
0.0004
0.002
0.0002
0.001
0.001
0.004
0.0003
0.002
0.001
0.005
0.001
0.0003
0.0003
0.001
0.0001
0.06
0.03
0.09
0.03
0.23
0.12
0.41
0.1
0.62
0.55
1.45
0.08
0.002
0.001
0.004
0.001
0.003
0.003
0.008
0.001
0.026
0.016
0.042
0.004
0.0024
0.0025
0.0067
0.0004
4.6
1.8
7.3
2.4
1.03
1.3
3.34
0.24
27/37
Figures 1,2,3,4: Nutrient composition of manure stored in a pit with no covering, in a heap with
no covering and in a heap with a roof overhead (Tittonell et al., 2010)
Table 8: Global production of phosphate based upon country (Jasinski,2015)
Global Phosphate Production
United States
Algeria
Australia
Brazil
Canada
China
Egypt
India
Iraq
Israel
Jordan
Kazakhstan
Mexico
Morocco and Western Sahara
Peru
Russia
Saudi Arabia
Senegal
South Africa
Syria
Togo
Tunisia
Vietnam
Other countries
World total (rounded)
Mine production (thousand tons) Reserves
2013
2014
31200
27100
1100000
1500
1500
2200000
2600
2600
1030000
6000
6750
270000
400
-76000
108000
100000
3700000
6500
6000
715000
1270
2100
35000
250
250
430000
3500
3600
130000
5400
6000
1300000
1600
1600
260000
1760
1700
30000
26400
30000
50000000
2580
2600
820000
10000
10000
1300000
3000
3000
211000
800
700
50000
2300
2200
1500000
500
1000
1800000
1110
1200
30000
3500
5000
100000
2370
2400
30000
2580
2600
300000
225000
220000
67000000
Table 9: Global potash production based upon country (Jasinski, 2015)
Global Potash Production
Mine production (thousand tons)
United States
Belarus
Brazil
Canada
Chile
China
Germany
Israel
Jordan
Russia
Spain
United Kingdom
Other countries
World total (rounded)
2013
960
4240
430
10100
1050
4300
3200
2100
1080
6100
420
470
—
34500
2014
850
4300
350
9800
1100
4400
3000
2500
1100
6200
420
470
150
35000
Reserves
K2O equivalent
Recoverable ore
1700000
3300000
300000
4700000
NA
NA
NA
NA
NA
2800000
NA
NA
250000
NA
200000
750000
50000
1100000
150000
210000
150000
40000
40000
600000
20000
70000
90000
3500000
29/37
Table 10: Inorganic contaminants, their maximim contaminant level (MCL), maximim contaminant goal (MCLG), and
possible side effects of exposure over the MCL.Treatment techniques (TT) vary with the chemical and if 10% of samples
surpass action levels then active responses are required to treat the water. (U.S.E.P.A., 2014)
Inorganic Chemicals
Contaminant
Antimony
Arsenic
Asbestos (fiber > 10
micrometers)
Barium
Beryllium
Cadmium
Chromium (total)
Copper
MCLG (mg/L)
MCL or TT1 (mg/L)
0.006
0
0.006
0.010 as of 01/23/06
7 million fibers per liter
(MFL)
2
0.004
0.005
0.1
1.3
7 MFL
Cyanide (as free cyanide)
Fluoride
Lead
0.2
4
zero
Mercury (inorganic)
Nitrate (measured as
Nitrogen)
0.002
10
Selenium
Thallium
0.05
0.0005
2
0.004
0.005
0.1
TT7; Action Level=1.3
Potential Health Effects from Long-Term Exposure Above the MCL (unless specified as
short-term)
Increase in blood cholesterol; decrease in blood sugar
Skin damage or problems with circulatory systems, and may have increased risk of
getting cancer
Increased risk of developing benign intestinal polyps
Increase in blood pressure
Intestinal lesions
Kidney damage
Allergic dermatitis
Short term exposure: Gastrointestinal distress; Long term exposure: Liver or kidney
damage
0.2
Nerve damage or thyroid problems
4
Bone disease (pain and tenderness of the bones); Children may get mottled teeth
TT7; Action Level=0.015 Infants and children: Delays in physical or mental development; children could show
slight deficits in attention span and learning abilities; Adults: Kidney problems; high
blood pressure
0.002
Kidney damage
10
Infants below the age of six months who drink water containing nitrate in excess of the
MCL could become seriously ill and, if untreated, may die. Symptoms include shortness
of breath and blue-baby syndrome.
0.05
Hair or fingernail loss; numbness in fingers or toes; circulatory problems
0.002
Hair loss; changes in blood; kidney, intestine, or liver problems
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