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Synthetic Fertilizers; Role and Hazards

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Synthetic fertilizers, benefits, toxicity, Nitrogen, phosphate, potassium
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Synthetic Fertilizers; Role and Hazards
AL-KAZAFY H. SABRY
ABSTRACT
Agriculture has relied on the use of natural fertilizers (substances that increase
the nutrient levels of soil) for most of human history. Synthetic fertilizers made
an entrance at the end of the 19th century and paved the way for modern
agricultural production. Their use increased crop yields and brought on an
agricultural revolution, the likes of which the world had not seen before. Synthetic
fertilizers continue to have far-reaching effects, both positive and negative, and
are likely to remain a part of human life for some time to come. These are
commonly used for growing all crops and play a great role in plants growth.
The importance of synthetic fertilizers are supplying of consistent amounts of
precise nutrients to the soil. They act on soil immediately unlike organic fertilizers
that need to break down before absorption. This immediate efficacy is especially
beneficial to dying or severely malnourished plants. Although of these benefits
of synthetic fertilizers, there are some negative effects such as these fertilizers
kill beneficial microorganisms in the soil that convert dead human and plant
remains into nutrient-rich organic matter. Nitrogen, phosphate and potassium
based synthetic fertilizers leach into groundwater and increase their toxicity,
causing water pollution. Fertilizers that leach into streams, rivers, lakes and
other bodies of water disrupt aquatic ecosystems. Synthetic fertilizers increase
the nitrate levels of soil. These harmful nitrites react with the hemoglobin in
the blood stream to cause methaeglobinaemia, which damages the vascular
and respiratory systems, causing suffocation and even death in extreme cases
(when blood methaemoglobin level is 80 percent or more). Plants that grow in
overly fertilized soil are deficient in iron, zinc, carotene, vitamin C, copper and
protein. Although synthetic fertilizers may produce impressively quick results
in your garden, or at commercial farms where growth equals profit, the liberal
and uncontrolled use of these synthetic compounds can lead to fertilizer pollution.
Assistant Researcher Professor, Pests and Plant Protection Department, National
Research Center, Giza, Egypt.
Corresponding Author E-mail: kazafyhassan@yahoo.com
111Synthetic Fertilizers; Role and Hazards
Key words: Synthetic fertilizers, benefits, toxicity, Nitrogen, phosphate,
potassium.
INTRODUCTION
Fertilizer defined as any organic or inorganic material of natural or synthetic
origin (other than liming materials) that is added to the soil to supply one or
more plant nutrients essential to the growth of plants. Or, Fertilizer is either a
chemical or organic compound that is applied to plant for the purpose of providing
supplemental nutrition to enhance all or a number of the plants growth
characteristics. Fertilizer also defined as any substance that contains one or
more essential plant nutrient elements. On the other hand, it can be defined as
plant nutrients existing naturally in the soil, atmosphere, and in animal manure.
However, naturally occurring nutrients are not always available in the forms
that plants can use, or in the quantities needed. So we add to them by applying
fertilizer, to make plants grow to their maximum potential.
Plants absorb nitrogen from the soil as both NH4 and NO3 ions, but because
nitrification is so pervasive in agricultural soils, most of the nitrogen is taken
up as nitrate. Nitrate moves freely toward plant roots as they absorb water.
Once inside the plant NO3 is reduced to an NH2 form and is assimilated to
produce more complex compounds. Because plants require very large quantities
of nitrogen, an extensive root system is essential to allowing unrestricted
uptake. Plants with roots restricted by compaction may show signs of nitrogen
deficiency even when adequate nitrogen is present in the soil. Today, virtually
all nitrogen materials are manufactured, usually from ammonia. Such materials
are less expensive; more concentrated, and are just as plant-available as the
organics used in the past. The production of fertilizers demands much energy
and generates considerable greenhouse gas (GHG) emissions. Kongshaug (1998)
estimated that the fertilizer production consumes approximately 1.2% of the
world’s energy and is responsible for approximately 1.2% of the total GHG
emissions. Ammonia (NH3) is the primary input for the majority of worldwide
nitrogen fertilizer production and all nitrogen fertilizers (DOE, 2000 and EFMA,
2000). According to Wood and Cowie (2004) Worldwide ammonia production is
largely based on modifications of the Haber-Bosch process where NH3 is
synthesized from a 3:1 volume mixture of hydrogen and nitrogen at elevated
temperature and pressure in the presence of an iron catalyst (Engelstad, 1985).
All the nitrogen used is obtained from the air and the hydrogen may be by
either of the following processes:
(a) Steam reforming of natural gas or other light hydrocarbons (Natural
Gas Liquids, Liquefied Petroleum Gas or Naphtha); or
(b) Partial oxidation of heavy fuel oil or coal. About 85% of world ammonia
production is based on steam reforming concepts (EFMA, 2000a). Natural
gas is the preferred hydrocarbon feedstock (Engelstad, 1985) with
112 Fertilizer Technology Vol. 1: Syntheis
approximately 80% of world ammonia capacity being based on natural
gas (EFMA, 2000 and Patyk, 1996).
Ammonium phosphate (NH4H2PO4) is produced by reacting phosphoric
acid (H3PO4) with anhydrous ammonia (NH3). Ammoniated superphosphates
are produced by adding normal superphosphate or triple superphosphate to
the mixture.
Microbial degradation of petroleum hydrocarbon is a very important factor
in the treatment of oil pollution both in aquatic and terrestrial environment
(Ibe and Ibe, 1984).
THE DIFFERENCES BETWEEN ORGANIC AND INORGANIC
FERTILIZERS
Fertilizers Can be Classified into two Groups: Organic or Inorganic.
1. Organic fertilizers are derived from living or once-living material,
including animal wastes, crop residues, compost and numerous other
by-products of living organisms. These fertilizers are the oldest known
form of fertilizers and have been used for hundreds if not thousands of
years to increase the yield or condition of agricultural and ornamental
plants. Organic fertilizers, as the name suggests are derived from
“organic” or naturally found materials and include such things as
composted vegetable materials and decomposed animal waste. They are
normally applied liberally as topdressing to agricultural fields or
production areas. The material needs to be decomposed as to allow the
release of the nutrients into the soil. Organics are normally “broad
spectrum” fertilizers that provide a whole spectrum of nutrients to the
plant with one application.
2. Inorganic fertilizers are derived from non-living sources and include most
of our man-made, petroleum fertilizers and commercial fertilizers. Man-
made and natural fertilizers contain the same elements, but man-made
fertilizers act more quickly.
Although the distinction between the two types is not always clear-cut,
urea, for example, is a naturally occurring organic compound, but chemically
synthesized urea is generally grouped with inorganic fertilizers. According to
the Minnesota Department of Agriculture, a natural organic fertilizer has to
be derived from either plant or animal materials containing one or more
elements (other than carbon, hydrogen, and oxygen) that are essential for plant
growth. Plant roots absorb the majority of their nutrients from the soil solution
as simple, inorganic ions (charged atoms or molecules). Larger molecules can
also be absorbed, but their rate of absorption is slow. Most inorganic fertilizers
dissolve readily in water and are immediately available to plants for uptake.
When used according to recommendations, these types of fertilizers efficiently
supply the required nutrients for plant growth and are safe for the environment.
113Synthetic Fertilizers; Role and Hazards
Organic fertilizers are more complex chemical substances that take time
to be broken down into forms usable by plants. They are slow-release type
fertilizers, compared to the quick-release characteristics of most inorganic
fertilizers. It is important to apply these organic fertilizers well before periods
of rapid plant growth.
Organic fertilizers usually have a low salt index, so larger amounts can be
applied at one time without causing injury to plant roots. With organic nitrogen
sources (except urea), one application can be made without having to be
concerned about losing most of the nitrogen to leaching. However, even organic
fertilizers applied at excessive rates can cause environmental degradation due
to nitrate leaching or runoff of soluble organic compounds.
The cost of organic fertilizers at garden centers per pound of nutrient
basis is usually higher than quick-release inorganic fertilizers.
Organic matter can increase soil drainage, aeration, water holding capacity,
and the ability of the soil to hold nutrients.
The beneficial effects of organic matter on soil structure can have a greater
effect on plant growth than the fertilizer value of some of these organic
materials. Synthetic Fertilizers are “Man made” inorganic compounds-usually
derived from by-products of the petroleum industry. Examples are:
SYNTHETIC FERTILIZERS OF NITROGEN (N)
Nitrogen is abundant in our atmosphere but rare in the soil–it is naturally
“fixed” (converted to soil availability) by bacteria on the roots of leguminous
plants, or by a strike of lightning. The Haber-Bosch process was developed in
the early 20th century to combine nitrogen from the air with hydrogen at high
temperature and pressure to make anhydrous ammonia (NH3), the basis for
all synthetic nitrogen fertilizers as well as munitions used in warfare. The
hydrogen source for the process is natural gas, a non-renewable resource that
currently accounts for 80 to 90 percent of the cost of fertilizer production. In
the conventional system, our very ability to feed ourselves is dependent upon a
non-renewable fossil fuel.
Synthetic nitrogen fertilizer became popular in the U.S. after World
War II when large stocks of leftover ammonium nitrate munitions were
marketed for agricultural use. However, the widespread adoption of synthetic
fertilizer and associated agricultural practices had a host of unintended
consequences to our environment, the quality of our foods, and the sustainability
of our food system (Fig. 1).
Synthetic fertilizers are banned from USDA’s organic production
standards, but were used in conventional food production on a massive scale.
More than 21 million tons of synthetic fertilizers were spread over American
114 Fertilizer Technology Vol. 1: Syntheis
Fig. 1: World consumption of N fertilizer until 2012.
farmland in 2010 alone, covering about one-eighth of the continental land mass.
Ammonium nitrate is a chemical compound with the formula NH4NO3. It is
composed of nitric acid and salt of ammonia. In room temperature, ammonium
nitrate appears in a white crystalline form and it is also colorless. Its melting
point is at 169.6 degrees Celsius or 337.3 degrees Fahrenheit. These crystals
are rhombohedral in shape but when they are subjected to temperatures above
32 degrees Celsius, they change to monoclinic crystals. Ammonium nitrate is
usually used as a solid material with an analysis of up to 34% nitrogen. It
contains both NH4
+ and NO3
forms of nitrogen, and is used as a source of
nitrogen in many blends of liquid and dry fertilizers, as well as being applied
directly. Pure ammonium nitrate is very hygroscopic and can be explosive under
certain conditions; however, present fertilizer grades of the material are
specially conditioned, and when stored and handled properly, pose no problem
or hazard.
Ammonium nitrate was said to be developed Germans which they used as
fertilizers instead of Chilean Nitrates since it is a lot cheaper. Commercially,
it is prepared by mixing nitric acid and ammonia salt. The reaction from the
two substances combined will form Ammonium Nitrate. The kind of ammonium
nitrate sold in the market contains an average of 33.5 percent of nitrogen. This
compound is very soluble in water; and if the water which ammonium nitrate
was dissolved at is heated, the by-product will be nitrous oxide which is
commonly referred to as laughing gas.
Role of Synthetic Nitrogen Fertilizer in Soil
Since the Green Revolution of the 1960s, substantial increases in cereal
production have allowed an ongoing rise in world population, which was exceeds
6.5 billion (United Nations, 2006). The gain in agricultural productivity has
been accomplished with the introduction of modern crop production practices
that rely on high-yielding varieties and heavy inputs of fertilizers and pesticides.
115Synthetic Fertilizers; Role and Hazards
This is approach is solely directed toward maximizing grain yield, without
regard to long-term impacts on the soil resource that is crucial for sustainable
cereal production. Nitrogen is the most important mineral nutrient for cereal
production, and an adequate supply is essential for high yields, especially with
modern cultivars. Consequently, a dramatic escalation has occurred in global
consumption of synthetic N, from 11.6 Tg in 1961 to 104 Tg in 2006 (FAO,
2009). This N is applied largely in the form of ammoniacal fertilizers produced
via the Haber Bosch process, an energy-intensive conversion of highly inert N2
to highly reactive NH3 that relies on natural gas for process energy and as a
source of H2 (Smil, 2001). Faced with rising energy costs and concomitant price
increases for N fertilizers, grain producers are under growing pressure to
maximize fertilizer N uptake eûciency (FNUE), deûned herein as 100 ×
(fertilized yield–unfertilized yield) × grain N concentration/fertilizer N applied.
Ammonium nitrate (as an example for synthetic nitrogen fertilizer) is
generally used as a fertilizer. It is actually sold in the form of pellets that are
coated with clay. The reason why it is very popular in agriculture is because of
the high nitrogen amount in this compound. Nitrogen is a very important plant
nutrient that assists in the growth and metabolic processes that the plant
undergoes. Agriculturists love using ammonium nitrate because it is a cheap
alternative to expensive fertilizers. It can also yield rapid growth and may
increase the fruit production capacity of a plant. It may also affect the quality
of green leafy vegetables since the nitrogen which is used by the plants is
actually very helpful in the process of photosynthesis. Another famous use of
ammonium nitrate is as an additive in explosives. Ammonium nitrate is
sensitive to heat and any application of this external factor can lead to explosion.
It is a strong oxidizing agent. This means that it can actually remove certain
electrons from other reactants when subjected to a redox chemical reaction.
This is the reason why ammonium nitrates are paired and added in combustibles
like TNT and others. Aside from that, ammonium nitrate is also the main
component of an explosive called ANFO which stands for Ammonium Nitrate
Fuel Oil. It is an explosive mixture which is used widely in mining. ANFO is
composed of 94 percent ammonium nitrate and 6 percent fuel oil. The
ammonium nitrate will serve as the oxidizing agent for the fuel. Another
interesting fact about this compound is that it is actually hygroscopic. A
hygroscopic substance is something that can easily collect water molecules
from the environment where it is placed. Because of this reason, ammonium
nitrates should not be stored in humid areas since water can easily affect the
compound’s explosive function. Ammonium nitrates are now regulated by the
government since it is already used to create fertilizer bombs. These are
improvised explosive devices that other people use in terrorism. Ammonium
nitrate can be very helpful in agriculture but correct storage and handling
should always be observed.
Nitrate fertilization generally, leads to higher levels of amino acids and
protein and increased growth (Bernier et al., 1993), and also to changes in
116 Fertilizer Technology Vol. 1: Syntheis
carbon metabolism including increased levels of organic acids and decreased
levels of starch (Scheible et al., 1997a), to changes in phytohormone levels
(Crawford, 1995) and to changes in allocation and phenology including a
decreased root: shoot ratio (Scheible et al., 1997b), altered root architecture
(Stitt and Feil, 1999).
Production of Ammonium Nitrate
Ammonia can be oxidized in air to produce nitric acid (HNO3). This nitric acid
can then be neutralized with more ammonia to produce a solution that is
typically 83% ammonium nitrate and 17% water. This solution can be used to
produce nitrogen fertilizer solutions or can be processed further to produce
solid ammonium nitrate (Figs. 2 and 3).
Fig. 2: Production of ammonia.
Fig. 3: Production of ammonium nitrate.
117Synthetic Fertilizers; Role and Hazards
Metabolism of Ammonium Nitrate
Generally, NO3; occurs in a much higher concentration than NH4 in the soil
solution and is free to move to the roots by diffusion and mass-flow. Plants,
however, tend to prefer NH3 to NO4 the preference varying with ambient pH
and temperature (Clarkson and Warner, 1979). It is therefore of interest to
study to what extent the presence of a low ambient NH4 concentration affects
the above mentioned processes in NO3-fed plants. Hedley et al. (1982) observed
a steady decline in the uptake of NO; by rape, when plants grown in small
volumes of soil became extremely P deficient. They suggested that this, together
with an increased uptake of Ca2+ was the cause of a higher uptake of cations
than of anions in the P deficient plants.
Usry (2013) reported that the air is about 80% nitrogen. In nature, this is
where the nitrogen nutrient originates. It can be brought into the soil by rain,
other plants (such as legumes: alfalfa, clover, peas, etc.), other organisms (such
as blue-green algae or microbes), the decay of other green plants, etc. There
are about 50,000,000,000 (fifty billion) microbes in a tablespoon of healthy
soil. Many more of these microbes are near the roots of plants. Their primary
job is to breakdown organic matter and to also feed plants. You could have
every element in its proper proportion available in the soil, but without the
microbial action plants would not be able to utilize them. Synthetic chemical
fertilizers actually inhibit, kill and alter this natural microbial activity which
is so very important to healthy plants. In healthy soil there are herds of microbes
near the roots of plants which out-compete pathogenic species and form a
protective layer on the surface of living plant roots. Microbes are essential in
making minerals available to plants and they also retain large quantities of
nutrients (such as nitrogen, phosphorus, potassium, sulfur, etc.) in their bodies
which help to prevent these nutrients from being leached or washed away.
Some microbes eat the dead cells of other microbes thus retaining the nutrients
within the soil. In the natural process, predator organisms which eat other
microbes get too much nitrogen in relation to the carbon that they require. It
takes 30 parts of carbon to assimilate one part of nitrogen in a normal soil.
When the predator microbe consumes excessive amounts of nitrogen, it is
released into the soil as nitrate. Plants can only use nitrogen in the nitrate
form. (For example, ammonia nitrogen can not be accessed by plants until it is
broken down into the nitrate form by microbial action). Nitrate is very, very,
very water soluble. Remember this point when you read further down.
118 Fertilizer Technology Vol. 1: Syntheis
Hazards of Ammonium Nitrate
Nitrogen is an essential constituent of proteins. In humans, when our proteins
(amino acids) breakdown, the nitrogen waste from the protein turns to ammonia
(NH3). Ammonia is very, very toxic, but the liver along with other body functions
quickly convert the ammonia into a less toxic substance, urea [(NH2)2CO].
While urea has some toxicity, we excrete it when we go to the bathroom or
sweat. However, the body is set up to process and handle nitrogen waste only
at a constant rate. If there is too much nitrogen waste for the body to handle at
one time, you will notice that you start to feel poorly. The highly toxic ammonia
content starts to buildup in the body (and possibly the less toxic urea buildup
if there are difficulties with the kidneys or other body systems). You might
personally observe this at those times you eat too much in proteins, such as
meat. A person will start to feel kind of lousy and kind of poisoned in an odd
sort of way. Some bacteria and parasites in the body also can dump toxic
ammonia into the system causing similar symptoms. So, you can imagine how
stressful this is on a body’s system when nitrogen from fertilizers enters the
body through the air, skin, or ingestion. The body can only handle so much at
a time. Also, ammonia can easily affect the brain which lacks the enzyme
essential for changing it into urea.
Ammonium nitrate (NH3NO3): Ammonia, a base, is extremely toxic to
humans. It has a sharp penetrating odor. Nitric acid is mixed with ammonia to
form a salt, ammonium nitrate. Ammonium nitrate can easily have reactions
if exposed to a variety of metals (e.g., iron, zinc, copper), acids, alkalis, solvents,
oil, grease, etc. You will notice that bags of fertilizer are often plastic coated
and sealed in order to keep contaminants out and gases in. Storage alone will
give off ammonia. Introduce heat to fertilizer and there will be further
instability. The release of toxic fumes is one of the main hazards associated
with the decomposition of Ammonium nitrate. Exposure to ammonium nitrate
can cause eye and skin irritation and burns. Inhalation exposure can result in
irritation of the nose, throat, and lungs. One can also experience nausea,
vomiting, flushing of the face and neck, headache, nervousness, uncontrolled
muscle movements, faintness and collapse. Because ammonia or nitrates
combine rapidly with water, feeling dehydrated is common. Lips will become
dry. The next time you handle or are exposed to chemical fertilizer, you will
probably notice some of these symptoms. Because the accumulation of ammonia
in the body can quickly lead to death, the urea cycle in humans is extremely
important.
Usry (2013) stated that nitrate is converted to a very toxic substance
(nitrite) within the digestive systems of human infants and also different
livestock and poultry and birds. During the first few months of an infants life
or in some baby animals or in some adult animals there exists a bacteria in the
stomach which changes the nitrate to nitrite. Nitrite is extremely toxic and
reacts with the hemoglobin in the blood to cut out the oxygen supply. It does
119Synthetic Fertilizers; Role and Hazards
not take a whole lot of substance to start producing toxic reactions. A baby will
suffocate if not given immediate medical attention. Signs are parts of the body
turning blue or the blood turning chocolate brown. These signs occur with both
humans and animals. Some livestock will go into convulsions and then die.
Pregnant mothers should also dramatically avoid fertilizers. Also, you certainly
would not want to expose any of your young pets (or some adult species) to
fertilizer. As a baby gets older, the hydrochloric acid in the stomach kills off
the bacteria which change the nitrate to nitrite. It should be noted that the
bacteria which convert the nitrate into the deadly nitrite can exist in adults to
various degrees
According to Department of Mines and Petroleum (2012) fires are avoided
by rigorously eliminating and reducing the amount of potential fuel, combustible
materials and dangerous contaminants in and around the ammonium nitrate
store. Fires involving ammonium nitrate cannot be extinguished by oxygen
deprivation because of the provision of oxygen from ammonium nitrate. Water
is the most effective means of fire fighting—attempts to smother fires with dry
chemical, carbon dioxide or foam extinguishers will not succeed. Suitably
designed, constructed and maintained ammonium nitrate storage facilities and
ammonium nitrate transfer equipment play a vital role in minimizing the risk
of fire–as does appropriate training of all relevant persons.
The risk of an explosion is decreased by reducing the potential for the AN
to be:
Heated, such as in a fire
• Contaminated
• Confined.
Given the nature of modern formulations of AN, explosions of solid AN
(excluding those initiated by explosives) without prior fire are very unlikely. If
all potential sources of fuel can be eliminated, the chance of an accidental
explosion is remote. However, such explosions can and have occurred with
concentrated hot solutions, particularly during manufacture.
Toxicity of Ammonium Nitrate to Human
There is limited information about the toxicity of ammonium nitrate;
unless otherwise stated the information is about nitrates in general.
Ammonium nitrate is well absorbed after ingestion, potentially absorbed
by inhalation; dermal absorption of nitrates may occur through abraded
areas (Mozingo et al., 1988).
The main mode of toxicity of nitrates is the induction of
methemoglobinaemia.
The primary systemic toxicity of nitrates is due to in vivo conversion to
nitrites.
120 Fertilizer Technology Vol. 1: Syntheis
The minimum lethal human exposure has not been established.
Inhalation exposure to 200 μg. m–3 for 2 hours caused no adverse health
effects (Hall and Rumack, 1999).
Five patients who ingested 6 to 234 g (from cold packs) suffered no severe
symptoms; three developed mild gastritis and two had mild hypotension
(Ellenhorn et al., 1997).
Occupational Exposure Standards: no data available.
A relatively small amount of the nitrogen contained in fertilizers applied
to the soil is actually absorbed by plants. The rest runs off into waterways,
where it creates massive “algal blooms.” The overgrown nitrate-fed algae
starve water of oxygen, suffocating fish and other aquatic life and creating
huge “dead zones” in lakes and oceans. The number of identified oceanic
dead zones has grown from 60 in 1995 to 405 in 2008. The Mississippi
River fertilizes a dead zone in the Gulf of Mexico that fluctuates in size
from 3,000 to 8,000 square miles.
Runoff nitrogen also leaches into groundwater, contaminating drinking
water and creating widespread health hazards.
Soil bacteria convert excess nitrates into nitrite ions, which, if ingested,
get into the bloodstream where they attach to hemoglobin molecules,
reducing their ability to carry oxygen and starving the body of oxygen.
Nitrates in drinking water used for infant formula can cause potentially
fatal blue-baby syndrome, and can cause serious health problems for
adults and children alike. High levels of nitrates and nitrites were found
in 25,000 community wells that provided drinking water to two thirds of
the nation’s population.
Excess nitrates in the soil sometimes convert to nitrosamines, which have
been shown to cause tumors in laboratory animals. Nitrate-contaminated
water is also linked to reproductive problems, urinary and kidney
disorders, and bladder and ovarian cancer.
Applying fertilizer releases oxidized nitrates, which contribute to the
formation of smog, act as greenhouse gases, and destroy protective ozone.
Nitrogen oxides also react with water in the atmosphere to form acid
rain.
SYNTHETIC FERTILIZERS OF PHOSPHATE (P)
Phosphate is an essential element needed in living organisms, and it is also a
non-renewable resource dependent exclusively on mined rock phosphates. An
input of phosphorus is crucial for food production since all plants need an
adequate supply of it for successful growth. A shortfall in phosphorus will result
in a reduction of crop yield (Fig. 4). Agriculture is by far the main user of
mined phosphorus globally, accounting for between 80–90% of the total world
demand (Childers et al., 2011).
121Synthetic Fertilizers; Role and Hazards
Fig. 4: World consumption of phosphate fertilizers
According to FAO data up to 2009, China, India and Europe already
consume about 60% of the global use of phosphate fertilizer. China is the largest
consumer of phosphorus fertilizers in the world with 34% of world total and
India is second with 19% of global consumption. Phosphorus consumption in
China and India show increasing trends (20% and 80% increase from 2002 to
2009, respectively), while in Europe consumption decreased by about 20% in
the same period (reflecting price increases and environmental restrictions).
On a worldwide scale, population growth, changes towards meat-rich diets
and growing demands for bioenergy crops will push an increasing demand for
phosphorus fertilizers in the future.
The phosphorous in synthetic fertilizer is usually triple super phosphate
0-46-0 (N-P-K) made by treating rock phosphate with phosphoric acid. Years
ago the phosphorous source was 0-20-0 or super phosphate. It was pretty darn
good even though it was created by a synthetic process. Rock phosphate was
made by treatment with sulfuric acid. It was a more balanced phosphate and
did not tie up trace minerals.
Ammonium phosphate is the salt of ammonia and phosphoric acid. It has
the formula (NH4)3PO4 and consists of ammonium cations and phosphate anion.
It is obtained as a crystalline powder upon mixing concentrated solutions of
ammonia and phosphoric acid. It is soluble in water, and the aqueous solution
on boiling loses ammonia.
According to Nyers et al. (1979) ammonium phosphate (NH4H2PO4) is
produced by reacting phosphoric acid (H3PO4) with anhydrous ammonia (NH3).
Ammoniated superphosphates are produced by adding normal superphosphate
or triple superphosphate to the mixture. The production of liquid ammonium
phosphate and ammoniated superphosphates in fertilizer mixing plants is
considered a separate process. Both solid and liquid ammonium phosphate
fertilizers are produced in the U.S. This discussion covers only the granulation
of phosphoric acid with anhydrous ammonia to produce granular fertilizer.
122 Fertilizer Technology Vol. 1: Syntheis
Total ammonium phosphate production in the U.S. in 1992 was estimated to
be 7.7 million megagrams (Mg) (8.5 million tons).
Production of Ammonium Phosphate
Ammonium phosphate (NH4H2PO4) is produced by reacting phosphoric acid
(H3PO4) with anhydrous ammonia (NH3). Ammoniated superphosphates are
produced by adding normal superphosphate or triple superphosphate to the
mixture. The production of liquid ammonium phosphate and ammoniated
superphosphates in fertilizer mixing plants is considered a separate process.
Two basic mixer designs are used by ammoniation-granulation plants: the
pugmill ammoniator and the rotary drum ammoniator. Approximately
95 percent of ammoniation-granulation plants in the US. use a rotary drum
mixer developed and patented by the Tennessee Valley Authority (TVA). The
basic rotary drum ammoniator-granulator consists of a slightly inclined open-
end rotary cylinder with retaining rings at each end, and a scrapper or cutter
mounted inside the drum shell. A rolling bed of recycled solids is maintained
in the unit. In the TVA process, phosphoric acid is mixed in an acid surge tank
with 93 percent sulfuric acid (H2SO4), which is used for product analysis control,
and with recycled acid from wet scrubbers. Mixed acids are then partially
neutralized with liquid or gaseous anhydrous ammonia in a brick-lined acid
reactor. All of the phosphoric acid and approximately 70 percent of the ammonia
are introduced into this vessel. Slurry of ammonium phosphate and 22 percent
water are produced and sent through steam-traced lines to the ammoniator-
granulator. Slurry from the reactor is distributed on the bed; the remaining
ammonia (approximately 30 percent) is sparged underneath. Granulation, by
agglomeration and by coating particulate with slurry, takes place in the rotating
drum and is completed in the dryer. Ammonia-rich off gases pass through a
wet scrubber before exhausting to the atmosphere. Primary scrubbers use raw
materials mixed with acid (such as scrubbing liquor), and secondary scrubbers
use pond water. Moist ammonium phosphate granules are transferred to a
rotary concurrent dryer and then to a cooler. Before being exhausted to the
atmosphere, these off gases pass through cyclones and wet scrubbers. Cooled
granules pass to a double-deck screen, in which oversize and undersize particles
are separated from product particles. The product ranges in granule size from
1 to 4 millimeters. The oversized granules are crushed, mixed with the
undersized, and recycled back to the ammoniator-granulator.
Triple Super Phosphate
This is produced by treating phosphate rock (apatite) with either sulfuric acid
or phosphoric acid, making it extremely acidifying (EPA, 2006). When applied
to the soil it reacts with calcium to form tri-calcium phosphate, which is water
insoluble, i.e. requiring microbial action for breakdown (Anderson, 2004). Even
in a soil with healthy microbial activity only about 15–20% of this phosphorous
123Synthetic Fertilizers; Role and Hazards
is easily available to plants, considerably less in soil which does not have good
microbial diversity (Wheeler and Ward, 1998). The production of each ton of
phosphoric acid is accompanied by the production of 4½ tons of calcium sulfate,
also known as phosphogypsum. This is a highly radioactive product and also
contains heavy metals and other impurities. By 1989 phosphogypsum waste
covered a total of 8500 acres, stacked between 3 and 60 meters high, causing
serious land, air and water pollution (Skorovarov et al., 1988).
Role of Synthetic Phosphates Fertilizers in Plants
When phosphorus fertilizers are applied, only a small proportion of it is
immediately available to plants. The rest is stored in soils in varying degrees
of availability. It is common for farmers to apply phosphorus in excess to make
it more available to crop plants, although this also increases the risk of most
phosphorus being lost via run-off, leaching or soil erosion, finally ending up in
lakes, rivers and oceans. This represents a financial loss and environmental
damage (Tirado and Allsopp, 2012). The authors stated also, Arable land losses
are due to inefficiencies in farm management: 33% of the phosphorus entering
the soil is lost by erosion (both wind and water). Only between 15–30% of the
applied phosphorus fertilizer is actually taken up by harvested crops. Losses
at the livestock production level are mostly due to improper management of
manure, about half of the phosphorus entering the livestock system is lost into
the environment instead of reapplied to farm soil where it could be used by
subsequent crops. Overall, about 90% of the phosphorus entering the system
is lost into the environment. Because of the increasing scarcity of high-grade
phosphate reserves, and the huge problem of losses to surface waters and
subsequent nutrient pollution and eutrophication, it is imperative that we “close
the loop” on the losses of phosphorus. In order to achieve a sustainable use of
phosphorus, two main strategies should be apply to any system:
1. Stop or minimise losses, by increasing efficiency in the use of phosphorus,
mostly in arable land and the food chain. Additionally, sustainable
phosphorus-use will benefit from shifting to plant-rich diets that are more
efficient users of phosphorus (and other resources) than meat-rich diets,
and from minimising food waste.
2. Maximise recovery and reuse of phosphorus, mostly of animal and human
excreta, and thus minimise the need for mined phosphorus.
Scientists describe phosphorus in soils as existing in four different “pools”
on the basis of their accessibility to plants (Syers et al., 2008):
1. The first pool of phosphorus is that which is in the soil solution and is
immediately available for uptake by plants.
2. The second pool is that phosphorus which is held on sites on the surface
of soil particles. This phosphorus can be readily transferred into soil
solution for uptake by plants if the concentration of phosphorus in the
124 Fertilizer Technology Vol. 1: Syntheis
soil solution is lowered by plants uptaking the phosphorus already in
solution.
3. The third pool of phosphorus is more strongly adsorbed to the soil particles
and is less readily extractable by plants but it can become available to
plants over time.
4. The phosphorus in the fourth pool is very strongly bonded to the soil
components and is only very slowly available to plants for uptake, often
over a period of many years.
Fig. 5: Role of synthetic phosphate in soil.
According to Shober (2012) the role of phosphate in soil is Phosphorus
must be dissolved in the soil solution in order to be taken up by plant roots.
The dissolved forms of plant-available P in the soil solution are called
orthophosphates (H2PO4
or HPO4
2–, depending on the soil pH) (Fig. 5). The
amount of P dissolved in the soil solution at any particular time is usually very
small. Once plant roots remove P from the soil solution, it is replenished by
the residual P in the soil. We previously discussed how soil microbes transform
organic forms of P in plant residues or organic soil amendments into plant-
available P. This process is called mineralization, and the end products are
soluble orthophosphates. Once in the soil solution, the orthophosphate form of
P can be taken up by plant roots. The soil solution can also be replenished from
several pools of inorganic (mineral) P in the soil. Solid P minerals in the soil
125Synthetic Fertilizers; Role and Hazards
can dissolve in the soil solution when concentrations of soluble P diminish.
This process, called dissolution can be compared with adding sugar to a glass
of iced tea. When solid sugar is added to tea, it will dissolve in the liquid.
Phosphorus can be attached to soil particles such as clay or specific minerals
that contain iron or aluminum. Phosphorus can detach from these soil particles,
thereby supplying P to the soil solution via a process called desorption. Finally,
solid rocks can be a source of P as they break down into soil over a long period
of time by a process called weathering. Just as soil solution P can be replenished
when the concentration of P becomes low, P can be removed from the soil solution
if the amount of P in the soil solution gets too high. Consider the iced tea
example again. If too much sugar is added to the tea, some of it will not dissolve
and will remain in solid form at the bottom of the glass. Similarly, when
concentrations of P in the soil solution are too high, some of the dissolved P
will form solid P minerals by a process called precipitation. Depending on soil
pH, precipitation can result in the formation of solid calcium phosphate minerals
(high soil pH) or aluminum and iron phosphate minerals (low soil pH).
Alternatively, P can be removed from the soil solution and attach to soil particles
like clays or iron and aluminum-bearing minerals via a process called
adsorption.
The Hazards of Synthetic Fertilizers of Phosphates
According to Tirado and Allsopp (2012) some phosphate contain low levels of
radionuclides, and some studies show increased radioactivity around phosphate
mining areas. Phosphogypsum is a by-product of phosphate rock processing,
and contains appreciable quantities of uranium. Phosphogypsum stockpiles
present a serious environmental problem, with potential hazard for human
health and pollution of the groundwater. Levels of radioactivity in phosphate
fertilizers vary widely worldwide, but they might represent a concern because
of their potential contribution to increased natural radioactivity in agriculture
soils in the long term. Some rock phosphate fertilizers contain small amounts
of the heavy metal cadmium. Because cadmium is highly toxic to humans,
there are concerns about its accumulation in agriculture soils and transfer
through the food chain. The EU is currently reviewing permitted levels of
cadmium in phosphorus fertilizers, with a view of lowering and harmonizing
safe levels. In Western countries, 54–58% of the cadmium found in the
environment comes from the application of mineral phosphate fertilisers to
agricultural land. In China, for example, recent analysis shows that high
intensity use of phosphate fertilisers in the Yangtze-Huaihe region lead to
elevated levels of cadmium in pond sediments of the watershed.
SYNTHETIC FERTILIZERS OF POTASSIUM (K)
Potassium fertilizers, like all chemical fertilizers, work by replacing lost
nutrients in soil that are depleted of essential minerals from repeated harvesting
126 Fertilizer Technology Vol. 1: Syntheis
activities. Commonly known as potash (element K), potassium was originally
discovered by farmers centuries ago when they found that wood ash in metal
pots was useful in aiding plant growth. Commercially produced potassium comes
in two types, muriate of potash and sulphate of potash. Both are salts that
make up part of the waters of the oceans and inland seas as well as inland
saline deposits (Fig. 6). Potassium chloride is bad on specific types of crops–
especially fruit crops. It’s also harsh on the soil. What we like as a potassium
source is potassium sulfate. It’s made from the salt of The Great Salt Lake.
Potassium fertilizers are an easy way to replace potassium deficient soil with
an essential nutrient for growth.
Fig. 6: World consumption of synthetic potassium fertilizer.
Role of Potassium in Plants
The main role of potassium in plants is helps plants maintain salt balance and
aids in uptake of nutrients, promotes development of thick cell walls for
improved winter hardiness and heat resistance, reduces damage due to drought
and disease, aids in water uptake, influences enzyme performance and enhances
overall health and vigor of plants. So, the role of potassium can be summarized
in few points:
1. Stimulates early growth,
2. Increases protein production,
3. Improves the efficiency of water use,
4. Is vital for stand persistence, longevity, and winter hardiness of alfalfa,
and
5. Improves resistance to diseases and insects.
The total K content of soils frequently exceeds 20,000 ppm (parts per
million). Nearly all of this is in the structural component of soil minerals and
127Synthetic Fertilizers; Role and Hazards
is not available for plant growth. Because of large differences in soil parent
materials and the effect of weathering of these materials in the United States,
the amount of K supplied by soils varies. Therefore, the need for K in a fertilizer
program varies across the United States. Three forms of K (unavailable, slowly
available or fixed, readily available or exchangeable) exist in soils. A description
of these forms and their relationship to each other is provided in the paragraphs
that follow. The general relationships of these forms to each other are illustrated
in (Fig. 7).
Fig. 7: Role of potassium in plants.
Potassium fertilizer production in Canada began before the 19th century
with the manufacture of POTASH from wood ashes. The industry expanded
until the late 19th century, when Germany became the world’s major potash
supplier by mining potash (potassium chloride) deposits. Potash deposits were
found in Saskatchewan in 1943 but development did not begin until 1954,
when the Potash Corporation of America sank the first shaft at Patience Lake.
There are presently numerous potash mines, mostly in Saskatchewan and to a
lesser extent in New Brunswick. The Saskatchewan potash deposits are
approximately 1000 m below the earth’s surface in central Saskatchewan, and
consist of a mineral deposit called sylvinite that contains both sodium chloride
and potassium chloride. The potash reserves in Saskatchewan and eastern
Manitoba are considered some of the premium world reserves of potash and
128 Fertilizer Technology Vol. 1: Syntheis
are estimated to contribute to world potassium production over the next number
of centuries. Commercially, potash fertilizers can be purchased in bulk in the
form of small fractions of crushed material. Rack Petroleum makes all kinds of
blends at its Fertilizer Plant.
Production of Potassium Fertilizer
The majority of mined KCl is used for obtaining various grade fertilizers based
on the particle size (granular, standard, fine, soluble). Granular KCl is often
applied in mixtures with other N and P based fertilizers to provide, in one
application, the nutrients required by the crops.
Another potassium fertilizer is potassium sulfate, which is frequently used
for crops where additional chloride from more common KCl fertilizer is
undesirable. Potassium sulfate can be extracted from the mineral langbeinite
or it can be synthetized by treating potassium chloride with sulfuric acid at
high temperature. By adding magnesium salts to potassium sulfate, a granular
potassium-magnesium compound fertilizer can also be produced (Fig. 8).
Fig. 8: Production of potassium fertilizer
The Hazards of Synthetic Fertilizers of Potassium
1. This product contains about 50% potassium and 50% chloride. In the soil
the chloride combines with nitrates to form chlorine gas. This kills
129Synthetic Fertilizers; Role and Hazards
microbes. Applying 1 pound of potassium chloride to the soil is equivalent
to applying 1 gallon of Clorox bleach. Or in other words: 2 ppm chlorine
are generally thought to be sufficient to sterilize drinking water–
potassium chloride application typically results in chloride levels as high
as 50–200 ppm.
2. Potassium chloride contains very high amounts of potassium, which can
result in an unbalanced phosphate: potash ratio. This ratio ideally ranges
from 2:1 (most soils) to 4:1 (grasses).
3. Excess potassium in the soil can lead to a calcium deficiency in plants,
since plants absorb calcium, magnesium and potassium largely in the
ratio in which they are present in the soil.
4. In the soil excess potassium causes a loss of structure. Reduced soil air
levels result in reduced root respiration and the production of toxic
compounds in plants. Reduced soil air and insufficient calcium each also
result in the reduction of soil microbes and the corresponding reduced
breakdown of organic matter/nutrient availability to plants.
5. In drilling potassium is used to “close” the soil, because it disintegrates
the clay particles (“ages” the clay) and effectively seals the soil.
6. Potassium is a soluble and highly leachable plant nutrient and it must
be supplied at a constant rate. Once applied it is taken up by the plant
rapidly. Although not necessarily harmful, over-application is of no added
benefit to plants and therefore is an unnecessary added cost to the grower.
Most plant experts discourage application of potassium to soil unless
tests reflect it is needed.
Hazards of Synthetic Fertilizers in General
According to Usry (2013) synthetic fertilizers can seriously deplete the
nutritional content of foods. Direct contact or exposure to synthetic chemical
fertilizers can kill babies or cause health problems in many people. Also, if you
have any type of urinary or kidney or liver or allergy or health difficulties, you
should especially avoid any type of exposure. The adverse effects of synthetic
chemical fertilizers are often underplayed and ignored despite their damage
being far reaching. Synthetic fertilizers can cause a vast array of symptoms,
some immediate, some signs showing up later, some effects on people and
animals are direct, and some effects are indirect. In the U.S., generally there
are three hyphenated numbers (for example: 15-5-10) on the front label of
fertilizer bags representing the percentage of each element by weight in the
bag. The elements represented are N, P, and K. Nitrogen, Phosphorus, and
Potassium. For example, the expression “15-5-10” means: 15% of the bags weight
contains Nitrogen, 5% of the bags weight contains phosphorous, and 10% of
the bags weight contains Potassium. Upon further reading on a bag, you will
see an analysis of the types of chemical compounds used in order to reach
these percentages. In other words, you will see a listing of the chemicals used
130 Fertilizer Technology Vol. 1: Syntheis
to reach those percentages of 15-5-10. The synthetic chemicals used to reach
these percentages of 15-5-10 can be different in different fertilizers. Some
chemicals are harsher than others, but they all end up being harmful to plants
and animals. These components written on the bag are “guaranteed” to be in
the bag by law. What is written on the bag must be in the bag. Some states
have slightly different regulations. These synthetic chemical compounds can
be directly and indirectly harmful in a number of ways. There are about 92
naturally occurring mineral elements. These are three of them (NPK). These
are essential for plant cell growth. There are about 10 other minerals which
are also essential for plant cell growth, but many other minerals are also very
important for healthy soil and plants. Oxygen, Carbon and Hydrogen are three
essential nutrients for plants (i.e., derived from water and carbon dioxide).
Their respective percentages in a whole plant are roughly 45%, 44%, 6%.
Compared to the percentages of these nutrients and the percentages of all the
other minerals; Nitrogen, Phosphorus, and Potassium actually have relatively
low percentages. However, these three elements have been over-played and
over-emphasized with the commercial, synthetic fertilizers for a variety of
reasons. It should be noted that there is a natural balance for healthy soil and
healthy plants which includes microbes and the environment. When the
synthetic and unnatural force feeding of chemicals occurs, the balance gets out
of wack and problems occur. So, adding just these three elements is as nutty
as feeding your children only cheerios, milk and juice. In fact, these three
elements added synthetically can dramatically upset how plants can absorb
other necessary mineral elements. These are only 3 of 13 essential elements,
but there are many other important ones also. It is not a natural, balanced
diet for plants.
Of the 29 fertilizers tested some were major and popular brands. Lead,
mercury, arsenic, cadmium, barium, chromium, nickel, beryllium, dioxin, etc.
can be pretty potent stuff. You can have kids and pets playing on the stuff,
people breathing the dust, these toxins getting into the water runoff,
agricultural accumulation in soils, plants and vegetables uptake many of these,
etc. The metals found in these fertilizers are known or suspected carcinogens,
reproductive and developmental, liver, and blood toxicants. In about a five
year period, 270,000,000 (270 million) pounds of toxic waste was sent to fertilizer
companies and farms according to reports from 44 different states. Regulations
are extremely strict if industry wishes to dispose of toxic waste in lined landfills.
However, regulations are relatively lax if they transfer the waste or resale it.
In other words, the simplest method of getting rid of toxic waste is just to
resale it. So, unwittingly we become the consumers who purchase toxic waste
to dump on our yards and parks and food crops and feed crops. Also, conventional
agriculture is a big culprit in taking all kinds of industrial waste, sludge, and/
or sewage sludge and dumping it onto fields as fertilization. To give you an
idea of how nutty this can go you can look at a relatively safe fertilizer: manure
(when it is composted). Conventional farmers are not required to delay
harvesting after applying fresh manure. Organic farmers must wait 90–
131Synthetic Fertilizers; Role and Hazards
120 days between application of raw manure and the harvest of any organic
crop which may be eaten raw, which allows the fresh manure time to compost
and thus, prevent the spread of any potentially dangerous bacteria. From
talking with different farmers and ranchers, I was amazed at how gross the
dumping of masses of chemicals onto fields really was.
The Fertilizer consumption (% of fertilizer production) in world was 94.67
in 2009, according to a World Bank report, published in 2010. Fertilizer
consumption measures the quantity of plant nutrients used per unit of arable
land. Fertilizer products cover nitrogenous, potash, and phosphate fertilizers
(including ground rock phosphate). Traditional nutrients—animal and plant
manures—are not included. For the purpose of data dissemination, FAO has
adopted the concept of a calendar year (January to December). Some countries
compile fertilizer data on a calendar year basis, while others are on a split-
year basis. This page includes a historical data chart, news and forecasts for
Fertilizer consumption (% of fertilizer production) in World (Fig. 9).
Fig. 9: World consumption of synthetic fertilizers.
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Mutants and transformants of tobacco (Nicotiania tabacum L. cv Gatersleben 1) with decreased expression of nitrate reductase have been used to investigate whether nitrate accumulation in the shoot acts as a signal to alter allocation between shoot and root growth. (a) Transformants with very low (1–3% of wild-type levels) nitrate reductase activity had growth rates, and protein, amino acid and glutamine levels similar to or slightly lower than a nitrate-limited wild-type, but accumulated large amounts of nitrate. These plants should resemble a nitrate-limited wild-type, except in responses where nitrate acts as a signal. (b) Whereas the shoot:root ratio decreases from about 3.5 in a well-fertilized wild-type to about 2 in a nitrate-limited wild-type, the transformants had a very high shoot:root ratio (8–10) when they were grown on high nitrate. When they were grown on lower nitrate concentrations their shoot:root ratio declined progressively to a value similar to that in nitrate-limited wild-types. Mutants with a moderate (30–50%) decrease of nitrate reductase also had a small but highly significant increase of their shoot:root ratio, compared to the wild-type. The increased shoot:root ratio in the mutants and transformants was due to a stimulation of shoot growth and an inhibition of root growth. (c) There was a highly significant correlation between leaf nitrate content and the shoot:root ratio for eight genotypes growing at a wide range of nitrate supply. (d) A similar increase of the shoot:root ratio in nitrate reductase-deficient plants, and correlation between leaf nitrate content and the shoot:root ratio, was found in plants growing on ammonium nitrate. (f) Split-root experiments, in which the transformants were grown with part of their root system in high nitrate and the other part in low nitrate, showed that root growth is inhibited by the accumulation of nitrate in the shoot. High concentrations of nitrate in the rooting medium actually stimulate local root growth. (g) The inhibition of root growth in the transformants was relieved when the transformants were grown on limiting phosphate, even though the nitrate content of the root remained high. This shows that the nitrate-dependent changes in allocation can be overridden by other signals that increase allocation to root growth. (h) The reasons for the changed allocation were investigated in transformants growing normally, and in split-root culture. Accumulation of nitrate in the shoot did not lead to decreased levels of amino acids or protein in the roots. However, it did lead to a strong inhibition of starch synthesis and turnover in the leaves, and to decreased levels of sugars in the root. The rate of root growth was correlated with the root sugar content. It is concluded that these changes of carbon allocation could contribute to the changes in shoot and root growth.
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Changes in the rhizosphere pH of rape plants (Brassica napus var. Emerald), grown at high root densities (> 90 cm cm−3) in a soil of low P status, were not associated with any detectable increase in the amount of extractable organic acids or their anions, or in the total amount of uronic acids in the soil. Microbial numbers in the rhizosphere soil and unplanted control soil were estimated by dilution plate counting, using an hydroxyapatite (HA) agar substrate, and those colonies capable of producing acid or of dissolving HA were identified. Neither the total number of colonies nor the number of acid-producing colonies and P solubilizing colonies bore any obvious relationship to the pH of the soil from which they were isolated. However, analysis of the major cation and anion concentrations in the plant tissue showed that more cations than anions were taken up by the rape plants during the period when the rhizosphere pH decreased. The milliequivalents of H+ or OH− required to produce the observed pH changes were calculated from the soil's pH buffer curve and found to agree closely with the difference between the milliequivalents of cations and anions taken up by the plant. A steady decline in NO3− uptake and a small increase in Ca2+ uptake created the cation-anion imbalance during the period of decreasing rhizosphere pH. H+ release from the roots must have occurred to maintain the charge balance across the root-soil interface and was the most likely cause of decrease in rhizosphere pH.
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The industrial synthesis of ammonia from nitrogen and hydrogen has been of greater fundamental importance to the modern world than the invention of the airplane, nuclear energy, space flight, or television. The expansion of the world's population from 1.6 billion people in 1900 to today's six billion would not have been possible without the synthesis of ammonia. In Enriching the Earth, Vaclav Smil begins with a discussion of nitrogen's unique status in the biosphere, its role in crop production, and traditional means of supplying the nutrient. He then looks at various attempts to expand natural nitrogen flows through mineral and synthetic fertilizers. The core of the book is a detailed narrative of the discovery of ammonia synthesis by Fritz Haber -- a discovery scientists had sought for over one hundred years -- and its commercialization by Carl Bosch and the chemical company BASF. Smil also examines the emergence of the large-scale nitrogen fertilizer industry and analyzes the extent of global dependence on the Haber-Bosch process and its biospheric consequences. Finally, it looks at the role of nitrogen in civilization and, in a sad coda, describes the lives of Fritz Haber and Carl Bosch after the discovery of ammonia synthesis.
Article
Additions of soluble phosphate to P-deficient Begbroke sandy loam delayed or completely prevented the fall in rhizosphere pH observed when rape was grown at high root densities in this soil (Parts I to III, this series). Whereas the pH of the unamended rhizosphere soil fell from 6–6.5 to 5.1–5.3 by day 41, the rhizosphere pH of soil with an extra 2 μmol P g−1 remained steady (6 to 6.5) until day 35, and that of soil with an extra 20 μmol P g−1 increased slightly from pH 6 to 6.4 during 41 days of growth. The increase in rhizosphere phosphatase activity with increasing severity of P deficiency appeared to be a response to increasing root density and decreasing concentration of soluble inorganic P in the soil. No significant change in levels of soil organic P was detected. Plants that acidified their rhizosphere (low P status) depleted acid-soluble forms of soil P and absorbed twice the amount of P which could be desorbed from the control soil in 10−2 M Ca(NO3)2at pH 6.1. Uptake of P by plants which did not acidify their rhizosphere (high P status) was never greater than the amount of P desorbable in 10−2m Ca(NO3)2 at pH 6.1, and was derived from alkali-soluble and resin-extractable forms of soil P. Cation uptake exceeded anion uptake in both low and high P plants, but the difference was greater in low P plants. These differences in cation and anion uptake (mEq) were approximately equal to the milliequivalents of H+ (OH−) required to produce the observed changes in rhizosphere pH. These results explain why models for P uptake based on in vitro measurements of physicochemical parameters governing phosphate diffusion in soil work well for P sufficient plants, but tend to underestimate P uptake by P deficient plants growing in soils in which soluble P levels are sensitive to pH change.
Article
Accumulation of nitrate in the shoot of low-nitrate reductase tobacco transformants leads to an increase of the shoot:root ratio to higher values than in nitrogen-sufficient wild-type plants, even though the transformants are severely deficient in organic nitrogen. In the present paper, wild-type plants and low- nitrate reductase transformants were grown on vertical agar plates to investigate whether this inhibition of root growth by internal nitrate (i) can be reversed by adding sugars to the roots and (ii) is due to slower growth of the main roots or to a decreased number of lateral roots. When grown with a low nitrate supply, the transformants resembled wild-type plants with respect to amino acid and protein levels, shoot-root allocation, lateral root frequency, and rates of growth. When the transformants were grown with a high nitrate supply in the absence of sucrose they grew more slowly and had lower levels of amino acids and protein than wild-type plants, but accumulated more nitrate and developed a high shoot:root ratio. Root length was not affected, but the number of lateral roots per plant decreased. The slower root growth was accompanied by an increase of the concentration of sugars in the roots. Addition of 2% sucrose to the medium partially reversed the high shoot:root ratio in the transformants, but did not increase the frequency of lateral roots. It is concluded that nitrate accumulation in the plant leads to decreased root growth via (i) changes in carbon allocation leading to decreased allocation of sugars to root growth, and (ii) a decrease in the number of lateral roots and a shift in the sensitivity with which root growth responds to the sugar supply.
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Phosphorites of sedimentary origin utilized in manufacturing of fertilizer contain uranium, thorium and products of their radioactive decay, as well as health-endangering compounds of cadmium, arsenic and fluorides. Some of them may transit into the phosphoric acid, when breaking down the phosphorites with sulphuric, acid, and then into the fertilizer. The purpose of the phosphoric acid cleaning is its decontamination from uranium and thorium as well as the removal of toxic cadmium. The above task can be achieved by solvent extraction. The paper presents the results of the extraction of uranium and cadmium from phosphoric acid using polyalkyl phosphasene and trioctyl amine, respectively. The extraction kinetics, equilibrium distribution of uranium and cadmium within the phases, the effect of extractant concentrations and temperature of the process is also discussed. The technological schemes for cleaning phosphoric acid from uranium and cadmium are given.