Why use fertilizers?
In order for a plant to grow and thrive, it needs a number of different chemical elements. The most important are:
* Carbon, hydrogen and oxygen - Available from air and water and therefore in plentiful supply
* Nitrogen, phosphorus, potassium (a.k.a. potash) - The three macronutrients and the three elements you find in most packaged fertilizers
* Sulfur, calcium, and magnesium - Secondary nutrients
* Boron, cobalt, copper, iron, manganese, molybdenum and zinc - Micronutrients
The most important of these (the ones that are needed in the largest quantity by a plant) are nitrogen, phosphorus and potassium. If you have read the articles How Cells Work and How Food Works, you have heard about things like amino acids, cell membranes and ATP. Nitrogen, phosphorus and potassium are important because they are necessary for these basic building blocks. For example:
* Every amino acid contains nitrogen.
* Every molecule making up every cell's membrane contains phosphorous (the membrane molecules are called phospholipids), and so does every molecule of ATP (the main energy source of all cells).
* Potassium makes up 1 percent to 2 percent of the weight of any plant and, as an ion in cells, is essential to metabolism.
Without nitrogen, phosphorus and potassium, the plant simply cannot grow because it cannot make the pieces it needs. It's like a car factory running out of steel or a road crew running out of asphalt.
If any of the macronutrients are missing or hard to obtain from the soil, this will limit the growth rate for the plant. In nature, the nitrogen, phosphorous and potassium often come from the decay of plants that have died. In the case of nitrogen, the recycling of nitrogen from dead to living plants is often the only source of nitrogen in the soil.
To make plants grow faster, what you need to do is supply the elements that the plants need in readily available forms. That is the goal of fertilizer. Most fertilizers supply just nitrogen, phosphorus and potassium because the other chemicals are needed in much lower quantities and are generally available in most soils. Nitrogen, phosphorus and potassium availability is the big limit to growth.
The numbers on a bag of fertilizer tell you the percentages of available nitrogen, phosphorus and potassium found in the bag. So 12-8-10 fertilizer has 12-percent nitrogen, 8-percent phosphorous and 10-percent potassium. In a 100-pound bag, therefore, 12 pounds is nitrogen, 8 pounds is phosphorous and 10 pounds is potassium. The other 70 pounds is known as ballast and has no value to the plants.
So why don't people need fertilizer to grow? Because we get everything we need from the plants we eat or from the meat of animals that ate plants. Plants are factories that do all of the work to process the basic elements of life and make them available to us.
What are fertilizers?
Any natural or manufactured material that contains at least 5% of one or more of the three primary nutrients - nitrogen (N), phosphorous (P), or potassium (K) - can be considered a fertilizer. Industrially manufactured fertilizers are sometimes referred to as "mineral" fertilizers.
There are several sources of plant nutrients . The two most important are organic manure and mineral fertilizers. When manure and crop residues are used, mineral fertilizers supply the outstanding nutrient balance needed for good crop yields. In most parts of the world, the balance to be supplied by mineral fertilizers is substantial.
Fertilizer production entails gathering raw materials from nature; treating them in order to purify them or increase their concentration; converting them into plant-available forms; and often combining them into products that contain more than one nutrient.
How are fertilizers manufactured?
Nitrogen
78% of the earth's atmosphere is nitrogen. However, the nitrogen we breathe is in a chemically inert form that plants (except legumes) cannot use. Large amounts of energy are required to convert this nitrogen to a form that can be used by plants.The production of ammonia from atmospheric nitrogen was made possible in the first part of the 20th century by the development of the Haber-Bosch process. It remains the only chemical breakthrough recognized by two Nobel prizes for chemistry , awarded to Fritz Haber in 1918 and Carl Bosch in 1931. The most important nitrogen-based fertilizers are urea and ammonium nitrate.
Phosphate
Phosphorus, in the form of phosphate (a salt of phosphoric acid) is mined from naturally occurring mineral deposits (phosphate rock) that were once sediments at the bottom of ancient seas. Rock phosphate is the raw material used in the manufacture of most commercial phosphate fertilizers. Ground rock phosphate was ounce applied directly to acid soils. However, due to low availability of phosphorous, high transport costs, and low crop responses, very little rock phosphate is currently used in agriculture. Phosphate rock processing consists in the separation of phosphate from the mix of sand, clay and phosphate that makes up the matrix layer.
Potash
The potassium used in fertilizers is found in a salt form called potash. Potash deposits are derived from evaporated sea water. They occur in beds of sediment at only a few places in the world. The largest deposit, in Saskatchewan, Canada is 2.7 to 23.5 metres (9 to 77.6 feet) thick and found at depths of 1000 to 10, 000 metres (3,200 to 10,000 feet). Solution mining methods are used to extract potash at greater depths. Conventional underground dry-shaft mining methods are used in mines as great as 1100 metres (3500 feet.). The ore is extracted from potash deposits by electrically operated mining machines and conveyed to the surface, where it is crushed. Using a flotation process, salt and clay particles are removed, the brine solution is dried, and the potash is sized by screening. The resultant coarse grade product is then ready for distribution. Fine particles remaining from the screening process are compacted into sheets that are crushed and screened to particle sizes suitable for blending.
Sulphur
Most of the sulphur used by the fertilizer industry is a by-product of other industrial processes.
Secondary and micronutrients
Secondary and micronutrients come from mineral deposits.
Common fertilizer products and intermediates
Nitrogen fertilizers
* Ammonia
* Ammonium sulphate (AS)
* Ammonium nitrate (AN)
* Calcium ammonium nitrate (CAN)
* Urea
Phosphate fertilizers
* Single superphosphate (SSP)
* Triple superphosphate (TSP)
* Diammonium phosphate (DAP)
* Monoammonium phosphate (MAP)
* Ground phosphate rock
Potash fertilizers
* Muriate of potash (MOP), also called potassium chloride
* Sulphate of potash
* Sulphate of potash magnesia
Magnesium fertilizers
* Kieserite
* Epsom salts
Complex fertilizers
* NPK fertilizers
* NP fertilizers
* NK fertilizers
* PK fertilizers
Terminology
Manufactured fertilizers are sometimes called "chemical" fertilizers. The nutrients in these fertilizers are all found in nature, but in insufficient quantities to sustain global agricultural production. Because these substances exist in nature, it is not strictly accurate to refer to the fertilizers that contain them as "chemical" or "artificial".
To distinguish its products from manure, legumes and other sources of crop nutrients, the fertilizer industry usually refers to "mineral" fertilizers. Although not very exact with respect to nitrogen (which is a gas), it is generally accepted that this is the most appropriate term.
Why do we need fertilizers?
Fertilizers increase crop yields
Plants need sun, water and nutrients to grow. The nutrients can be taken from air or soil. If there is an ample supply of nutrients in the soil, crops are more likely to grow well and produce high yields. If even one of the nutrients needed is in short supply, plant growth is limited and crop yields are reduced.
Fertilizers are needed to obtain high yields because they supply crops with the nutrients the soil lacks. By adding fertilizers, crop yields can often be doubled or even tripled. The UN Food and Agriculture Organization (FAO) Fertilizer Programme undertook extensive demonstrations and trials in 40 countries over a period of 25 years. The weighted average increase resulting from the best fertilizer treatment for wheat was about 60%.
Fertilizers contribute to efficient use of land and water
Fertilizers ensure the most effective use of both land and water. Where rainfall is low or crops are irrigated, the yield per unit of water used may be more than doubled and the rooting depth of the crop increased through fertilizer application.
Organic manure improves fertilizer efficiency
Before fertilizers are applied, all available plant nutrient sources (e.g. cow-dung, pig excreta, chicken droppings, vegetable wastes, straz, maize stover and organic materials) should be used. They should be well composted and allowed to decompose before being applied to the soil.
Although the nutrient content of organic manure is low and variable, it is very valuable. It increases soil fertility by:
* improving soil structure
* reducing soil erosion
* regulating soil temperature
* helping soil to store more moisture
* providing food for soil organisms
Integrated Plant Nutrition Systems
The application of organic manure is often the basis for successful use of mineral fertilizers. The combination of organic manure, other organic matter and mineral fertilizers provides ideal conditions for crop growth. Organic manure and other organic matter improve soil properties. Mineral fertilizers supply the needed plant nutrients .
Because of the level of crop production required for farmers to respond adequately to market demand, the use of organic manure alone is not sufficient. Mineral fertilizers are also needed. Even in countries where a high proportion of organic waste is used as manure (and to supply other organic matter), mineral fertilizer consumption has risen steadily.
Encouraging the adoption of best practices
The fertilizer industry works closely with farmers to reduce its environmental footprint.
Fertilizer Best Management Practices
On the production side, companies are improving operational practices, investing in effluent control, reducing emissions to air, soil and water, and restructuring production plants.
On the consumption side, the industry promotes education concerning the safest and most efficient techniques for using fertilizers in co-operation with farmers’ associations and industry and governmental organizations.
This strategy aims at optimizing nutrient use efficiency to reduce losses. Fertilizer Best Management Practices (FBMPs) have been developed by the fertilizer industry, research institutions and farmers' associations to achieve this objective.
What is a soil?
Soil is the uppermost surface of the earth, which has been slowly transformed by decomposition due to the effects of weather, vegetation and human activities. The parent material from which soil is formed can be the underlying rock, deposits from rivers and seas (alluvial soils) or the wind (aeolian soils), or volcanic ash.
What are the soil constituents?
Soils is composed of:
* mineral particles
* the products of weathering
* organic matter
* water and air
Soil texture and structure are of special importance for soil fertility and plant growth:
* Solid particles are classified by size into gravel and stones, sand, silt and clay.
* Soil texture refers to the relative proportions of sand, silt and clay in the soil. Depending on the soil's texture, it is described as sand, sandy loam, loam, clay loam, clay, etc. Soil can also be characterized as light, medium or heavy based on its workability.
* Soil structure refers to the aggregation of the finer soil particles into crumbs or larger sizes.
What does soil do for plants?
Soil supports plants by providing a permeable layer for their roots. It stores plant nutrients and water.
Depending on their composition, soils differ in their ability to supply plant nutrients.
What determines soil fertility?
Factors of soil fertility
Factors determining soil fertility
The main factors that determine soil fertility are:
* soil organic matter (including microbial biomass)
* soil texture
* soil depth
* nutrient content
* storage capacity (absorption capacity)
* soil reaction
* absence of toxic elements
Contrary to what is widely believed, the colour of the soil reveals very little about its fertility.
How does soil hold nutrients and release them?
Decomposing rock material forms soils and releases plant nutrients. The original mineral content of this material - and the nature and intensity of the decomposition process - determine the kind and amount of nutrients released. Clay and organic matter retain nutrients in a plant-available form, that is, the nutrients are attached to the soil constituents.
Soil's ability to retain a certain amount of nutrients determines its natural fertility.
Nutrients, which carry positive and negative charges (cations an anions), are attracted by the clay and organic matter in the same way that metal filings are attracted by a magnet.
Soil water containing the nutrients in dissolved plant-available form is called the soil solution. Nutrients can only be taken up by roots in dissolved form. Therefore, they have to be released from the storing complex into the soil solution to be plant-available.
The process of nutrient adsorption (the attraction of water molecules and of ions on the surface of clay or organic matter particles) and release to the soil solution is very important. The difference in the adsorption strength of the cations and anions helps determine how and when fertilizers (particularly nitrogen fertilizers) should be applied to achieve the highest efficiency and avoid pollution by leaching.
Organic matter can adsorb more nutrients than a comparable amount of clay. It is therefore important to build up the organic matter, especially in degraded tropical soils with less ability to adsorb the mineral component.
Soil organisms increase soil fertility
The activities of soil organisms are indispensable for high soil fertility and good crop production. Most of these activities are beneficial for the farmer. Soil organisms decompose organic matter to produce humus; aggregate soil particles to provide better structure; protect roots from diseases and parasites; retain nitrogen and other nutrients; produce hormones that help plants grow; and can convert pollutants that find their way into the soil.
After being mixed into the soil and ingested by earthworms, the insoluble forms of nitrogen, phosphate and sulphur contained in the particles.
Farmers need good knowledge of their soils in order to improve their fertility.
How Soil Fertility Relates to Sustainability Concerns
Food production /
economic development
* Greater soil fertility is needed to support higher yields, in order to feed a growing population and increase farmers' return per unit of cultivated land.
* Soils must be rich in all the necessary nutrients if food products are to contain the optimal nutritional balance.
Climate change
* Carefully managing the nitrogen applied in fertilizers can reduce losses to the atmosphere, where it may take the form of nitrous oxide (N2O), a potent greenhouse gas.
* Plants remove carbon dioxide (CO2) from the atmosphere as they grow. Increased crop yields and the resulting crop residues can augment the carbon-containing organic matter, generally producing richer soils.
* Greater soil fertility supports higher yields of renewable energy sources (e.g. bioenergy crops).
Water
* Good plant nutrition favours more efficient water use.
* Fertile soils support plant growth, reducing nutrients runoff to ground and surface water, and limiting water over-enrichment.
* Fertile soils that contain adequate organic matter retain more water. This is an important aspect of the water cycle.
Desertification
* Rich soils favour the growth of crop cover, which helps control erosion.
* The increased water retention of rich soils also helps fight desertification.
Genetic heritage
* The microorganisms found in soil are a huge reservoir of biological diversity, much of which is not yet fully understood, integrated into agricultural management practices or otherwise used.
Culture / leisure
* Healthy, fertile soil is a powerful symbol in many cultures. It represents the bounty of nature.
* Increasing the fertility of agricultural land can prevent marginal land and valuable habitat areas from being cultivated. This may also make more land available for leisure purposes, such as parks.
What are plant nutrients?
The essential nutrients
Sixteen nutrients are essential for the growth of most plants. They are derived from the surrounding air, water and soil.
* From air: carbon as carbone dioxide (CO2)
* From water: hydrogen and oxygen
* From soil, fertilizer and animal manure:
o nitrogen N
o phosphorus P
o potassium K
o calcium Ca
o magnesium Mg
o sulphur S
o iron Fe
o manganese Mn
o zinc Zn
o copper Cu
o boron B
o molybdenum Mo
o chlorine Cl
Other chemical elements are also taken up by plants. While these elements are beneficial to some plants, they are not essential to the growth of all of them.
The role of nutrients
Soils may be naturally low in nutrients, or they may become deficient due to nutrient removal by crops over the years without replenishment - or when high-yielding varieties are grown that have higher nutrient requirements than do local varieties.
Learn
2 main types of nutrients
The two main types of nutrients
All of the essential nutrients are important but in varying quantities
* Macronutrients are needed by plants in large quantities. The "primary nutrients" are nitrogen, phosphorus, and potassium. Today, sulphur is also considered a key macronutrient. Macronutrients include both primary and secondary nutrients.
* Micronutrients (or "trace elements") are required in very small amounts for correct plant growth. They need to be added in small quantities when they are not provided by the soil.
Every plant nutrient, whether required in large or small amounts, has a specific role in plant growth and food production. One nutrient cannot be substituted for another.
Nitrogen N
Nitrogen is the motor of plant growth. It is taken up from the soil in the form of nitrates or ammonium. As the essential constituent of proteins, nitrogen is involved in all the major processes of plant development and yield formation.
Phosphorus P
Phosphorous performs a key role in the transfer of energy. It is essential for photosynthesis and other chemico-physiological. Phosphorous is indispensable for cell differentiation, as well as for the development of the tissues that form a plant's growing points. Most natural and agricultural soils are phosphorus deficient. When there are problems with phosphorous fixation, this also limits its availability.
Potassium K
Potassium activates more than 60 enzymes, (the chemical substances that govern life and play a vital part in carbohydrate and protein synthesis). It improves a plant's water regime and increases tolerance to drought, frost and salinity. Plants that are well supplied with potassium are less affected by disease.
Sulphur S
Sulphur is an essential constituent of protein. It is also involved in the formation of chlorophyll. Sulphur is as important in plant growth as phosphorous and magnesium, but its role has often been underestimated.
Magnesium Mg
Magnesium is the central constituent of chlorophyll, the green pigment in leaves that functions as an acceptor of the energy supplied by the sun: 15-20% of the magnesium in a plant is found in the green parts. Magnesium is also involved in enzyme reactions related to energy transfer.
Calcium Ca
Calcium is required for root growth and as a constituent of cell wall materials. Most soils contain sufficient plant-available calcium. Deficiencies may occur in strongly calcium-depleted tropical soils. Calcium is usually applied to limit or reduce soil acidity.