Saturday, November 30, 2013

Ammonia...Why is it used as a nitrogen fertilizer?

Ammonia (NH3) is the foundation for the nitrogen (N) fertilizer industry. It can be directly applied to soil as a plant nutri­ent or converted into a variety of common N fertilizers. Special safety and management precautions are required.
Ammonia application (Farm Progress)

Almost 80% of the Earth’s atmosphere is composed of N2 gas, but it is in a chemically and biologically unusable form. In the early 1900s, the process for combining N2 and hydrogen (H2) under conditions of high temperature and pressure was devel­oped. This reaction is known as the Haber-Bosch process: [3H2 + N2 à 2 NH3]

A variety of fossil fuel materials can be used as a source of H2, but natural gas (methane) is most common. Therefore, most NH3 production occurs in locations where there is a readily available supply of natural gas.
Ammonia is a gas in the atmosphere, but is transported in a liquid state by compressing or refrigerating it below its boiling point (-33 ºC). It is shipped globally in refrigerated ocean vessels, pressurized rail cars, and long-distance pipelines.

Chemical Properties
Ammonia                   NH3
N Content                  82% N
Boiling Point               -33 ºC (-27 ºF)
Aqua Ammonia          (NH4OH)
N Content                   20 to 24% N
pH                               11 to 12
Pressurized ammonia tank
Agricultural Use
Ammonia has the highest N content of any commercial fertilizer, making it a popular source of N despite the potential hazard it poses and the safety practices that are required for its use. When NH3 is applied directly to soil, it is a pressurized liquid that immediately becomes a vapor after leaving the tank. Ammonia is always placed at least 10 to 20 cm (4 to 8 in.) below the soil surface to prevent its loss as a vapor back to the atmosphere. Various types of tractor-drawn knives and shanks are used to place the NH3 in the correct location. 
Ammonia knives for subsoil application

Ammonia will rapidly react with soil water to form ammonium (NH4+), which is retained on the soil cation exchange sites. Ammonia is sometimes dissolved in water to produce “aqua ammonia”, a popular liquid N fertilizer. Aqua ammonia does not need to be injected as deeply as NH3, which provides benefits during field application and has fewer safety considerations. Aqua ammonia is frequently added to irrigation water and used in flooded soil conditions.

Management Practices
Handling NH3 requires careful attention to safety. At storage facilities and during field application, appropriate personal protection equipment must be used. Since it is very water soluble, free NH3 will rapidly react with body moisture, such as lungs and eyes, to cause severe damage. It should not be transferred or applied without adequate safety training.
Immediately after application, the high NH3 concentration surrounding the injection site will cause a temporary inhibition of soil microbes. However, the microbial population recovers as NH3 converts to NH4+, diffuses from the point of application, and then converts to nitrate. Similarly, to avoid damage during germination, seeds should not be placed in close proximity to a recent zone of NH3 application. Inadvertent escape of NH3 to the atmosphere should be avoided as much as possible. Emissions of NH3 are linked to atmospheric haze and changes in rain
 water chemistry. The presence of elevated NH3 concentrations in surface water can be harmful to aquatic organisms.
Proper safety measures (CTIC)

Non Agricultural Uses
Over 80% of NH3 production is used for fertilizer, either for direct application or converted to a variety of solid and liquid N fertilizers. However, there are many important uses for NH3 in industrial applications. Household cleaners are made from a 5 to 10% solution of NH3 dissolved in water (to form ammonium hydroxide). Because of its vaporization properties, NH3 is used widely as a refrigerant.

Saturday, November 16, 2013

Potassium nitrate: a versatile soluble fertilizer

Potassium nitrate (KNO3) is a soluble source of two major essential plant nutrients. It is commonly used as a fertilizer for high-value crops that benefit from nitrate (NO3-) nutrition and a source of potassium (K+) free of chloride (Cl-).
Prilled potassium nitrate

Potassium nitrate fertilizer (sometimes referred to as nitrate of potash or NOP) is typically made by reacting potassium chloride (KCl) with a nitrate source. Depending on the objectives and available resources, the nitrate may come from sodium nitrate, nitric acid, or ammonium nitrate. The resulting KNO3 is identical regardless of the manufacturing process. Potassium nitrate is commonly sold as a water-soluble, crystalline material primarily intended for dissolving and application with water or in a prilled form for soil application. Traditionally, this compound is known as saltpeter.

Chemical Properties
Chemical formula:              KNO3
N content:                           13%
K2O content:                       44 to 46%
Water solubility (20°C):       316 g/L
Solution pH:                         7 to 10
 Agricultural Use
Potassium nitrate granules for dissolving
The use of KNO3 is especially desirable in conditions where a highly soluble, chloride-free nutrient source is needed. All of the N is immediately available for plant uptake as nitrate, requiring no additional microbial action and transformation in the soil. Growers of high value vegetable and orchard crops sometime prefer to use a nitrate-based source of nutrition in an effort to boost yield and quality. Potassium nitrate contains a relatively high proportion of K, with a N to K ratio of approximately 1:3. Many crops have high K demands and can remove as much or more K than N at harvest.

Applications of KNO3 to the soil are made before the growing season or as a supplement during the growing season. A diluted solution is sometimes sprayed on plant foliage to stimulate physiological processes or to overcome nutrient deficiencies. Foliar application of K during fruit development can be advantageous for some crops, since this growth stage often coincides with high K demands during the time of declining root activity and nutrient uptake. It is also commonly used for greenhouse plant production and hydroponic culture.

Management Practices
Both N and K are required by plants to support harvest quality, protein formation, disease resistance, and water use efficiency. Therefore, KNO3 is often applied to soil or through the irrigation system during the growing season to support healthy growth.
Potassium nitrate prills are white

Potassium nitrate accounts for only a small portion of the global K fertilizer market. It is primarily used where its unique composition and properties are able to provide specific benefits to growers. It is easy to handle and apply, and is compatible with many other fertilizers. This includes usage for many high-value specialty crops, as well as grain and fiber crops.
Water solubility of common potassium fertilizers

The relatively high solubility of KNO3 under warm conditions allows for a more concentrated solution than for other common K fertilizers. Careful water management is needed to keep the nitrate from moving below the root zone.

Non Agricultural Uses
Potassium nitrate has long been used for fireworks and gunpowder. It is now more commonly used in food to maintain the quality of meat and cheese. Specialty toothpastes often contain KNO3 to alleviate tooth sensitivity. A mixture of KNO3 and sodium nitrate (NaNO3) is used for storing heat in solar energy installations.

Monday, November 11, 2013

Potassium Magnesium Sulfate fertilizer: Langbeinite

Langbeinite is a unique source of plant nutrition since three essential nutrients are naturally combined into one mineral. It provides a readily available supply of K, Mg, and S to growing plants.

Langbeinite is a distinctive geological material found in only a few locations in the world. Commercial supplies of lang­beinite come from underground mines near Carlsbad, New Mexico (USA), which were first commercially developed in the 1930s. These deposits were formed millions of years ago when a variety of salts, including langbeinite, were left behind after the evaporation of ancient ocean beds. These salt deposits were buried deep beneath hundreds of meters of sediment. The langbeinite deposit is currently mined with large boring machines, washed to remove impurities, and then crushed to various particle sizes. Langbeinite is considered a potash (or K-containing) fertilizer, even though it also contains valuable Mg and S. Traces of iron oxide impurities give some langbeinite particles a reddish tint.
Underground mining in New Mexico

 Chemical Properties
Property:                             K2SO4.2MgSO4
Fertilizer analysis:                  21 to 22% K2O
                                             10 to 11% Mg
                                             21 to 22% S
Water solubility (20 ºC)           240 g/L
Solution pH                            approx. 7

Agricultural Use
Langbeinite is a popular fertilizer, especially where several nutrients are needed to provide adequate plant nutrition. It has an advantage of having K, Mg, and S all contained within a single particle, which helps provide a uniform distribution of nutri­ents when it is spread in the field. Due to economics, langbeinite may not be recommended to meet the entire K requirement of a crop. Instead, application rate may be based on the need for Mg and/or S.

Langbeinite is totally water soluble, but is slower to dissolve than some other common K fertilizers because the particles are denser than other K sources. Therefore, it is not suitable for dissolving and application through irrigation systems unless finely ground. It has a neutral pH, and does not contribute to soil acidity or alkalinity. This differs from other common sources of Mg (such as dolomite) which will increase soil pH and from elemental S or ammonium sulfate which will lower the soil pH.

Langbeinite fertilizer
It is frequently used in situations where a fertilizer free of Cl- is desirable, such as with crops sensitive to Cl- (some vegeta­bles and certain tree crops). Langbeinite is a nutrient-dense fertilizer with a relatively low overall salt index. Particular sources of langbeinite have been certified for use in organic crop production in some countries.

Management Practices
Langbeinite has no restrictions for environmental or nutritional use when used at typical agronomic rates. One form of langbeinite is sold as a feed grade dietary source of K, Mg, and S for animals and poultry. All three of these nutrients are required for animal nutrition and each has a specific metabolic role required for optimal animal health. This feed material is “recognized as safe” by government agencies. As with all plant nutrients, best management practices should be observed to properly utilize this resource. A particular particle size should be matched with the specific need. 
Most potash fertilizers are extracted from great depths
Non-agricultural Use:
There are no major industrial applications for langbeinite outside of agriculture.

Some examples of commercial langbeinite fertilizers produced in North America include the products of K-Mag (Mosaic Co), and TRIO (Interpid Potash).

Monday, November 4, 2013

The Phosphorus Crisis: When Is It Coming, and Is There a Simple Solution?

 Don't believe everything you see and hear.

Biologist Mohamed Hijri presents an interesting TED talk entitled: 
A simple solution to the coming phosphorus crisis

He talks about two issues associated with the phosphorus nutrition of plants. The first is the finite nature of phosphate reserves (the source of phosphorus fertilizer), and the second is algal blooms arising from losses of phosphorus from agricultural fields. We appreciate the recognition of the important role of phosphorus in supporting agricultural production for a future global population of over 9 billion.   But he presents many statements as fact without any supporting references. Many of these statements contradict a considerable volume of published peer-reviewed scientific and technical literature. IPNI welcomes discussion of issues associated with phosphorus fertilizer use, and the opportunity to clarify public perception of those issues. Applying the right source of phosphorus fertilizers at the right rate, right time and right place is consistent with maintenance of an appropriate level of mycorrhizae in agricultural soils. 

This statement of correction is posted in the IPNI website:
Biologist Mohamed Hijri presents a very polished lecture in French on the important topic of two issues associated with the phosphorus nutrition of plants. The first is the finite nature of phosphate reserves; the source of phosphorus fertilizer, and the second is algal blooms arising from losses of phosphorus from agricultural fields.

While the lecture is well presented, certain statements are presented as fact without any reference to supporting literature. Here we point out that these statements contradict a considerable volume of published peer-reviewed scientific and technical literature

1. “There is a global phosphorus crisis, and no one is talking about it.” In recent years, there has been considerable international activity and discussion of phosphorus issues. One example is the organization called Global TraPs – the Global Transdisciplinary Processes for Sustainable Phosphorus Management, a multi-stake holder forum based jointly in Germany and the U.S. In addition, the International Fertilizer Development Center published a technical bulletin (Van Kauwenbergh, 2010) called “World Phosphate Rock Reserves and Resources” which, while highlighting the industry’s concern for finite resources, indicates that the figures used by Professor Hijri are out of date, and shows that current reserves are considerably larger, sufficient for over 300 years at current rates of extraction. The reserve figures in this publication are in agreement with the USGS (2013) publication of mineral commodity summaries. In addition, the International Plant Nutrition Institute has published a 2013 article “World Reserves of Phosphate Rock…a Dynamic and Unfolding Story” which points out that over the past decade or so there has been concern that the world would soon deplete its phosphate rock resources, and face a catastrophic phosphorus shortage; however, recent and thorough estimates of world supply indicate that a crisis is not imminent, and that we will not soon run out of phosphate rock.

2. “Peak phosphorus will occur by 2030 and all reserves will be gone by 2100.” As pointed out above, more recent published material (e.g. Scholz and Wellmer, 2013) and presentations show that this statement, usually attributed to Cordell (2009), is based on outdated reserve estimates and methodology and has been strongly criticized because it over estimates the urgency of the phosphorus supply risk. The modeling approach in the graph used to demonstrate the peak of phosphate production occurring in 2030 has also been shown to be inaccurate and unrealistic (Hendrix, 2011). In addition, Sutton et al. (2013; figure 2.9 on page 15) point out that many other important commodities, including crude oil and natural gas, and the important micronutrient zinc, have much shorter estimates for reserve life than does phosphate.

3. “Only 15% of [phosphorus fertilizer applied] goes to the plant. 85% is lost. It goes into the soil, ending its journey in the lakes.” While eminent soil fertility scientists recognize that soil reactions with applied phosphate limit its direct uptake by plants in the short term, the long term recovery can approach 90%, because phosphorus is retained in the soil in slowly available forms (Syers et al., 2008). Estimates of the global phosphorus cycle depicted in Figure 3.2 on page 23 of Sutton et al. (2013) indicate that the total transfer of phosphorus from the terrestrial ecosystem to fresh waters is considerably less than 85% of the total input of phosphorus to agricultural soils. It also indicates that much of this transfer arises from erosion, a process that carries indigenous soil phosphorus as well as that applied in the form of fertilizers. So, the actual loss of phosphorus from fertilizer is both smaller and less direct than indicated in the presentation by Professor Hijri. Industry is engaging 4R Nutrient Stewardship to reduce these losses; examples include a collection of articles under the topic of Lake Erie P Issues and a list of activities at
4. The presentation suggests that a plant with mycorrhizae will take up 90% of applied phosphorus in comparison to the 15% taken up by plants in conventional agriculture. First, this comparison is misleading, since two factors are changing at once, both rate of application and mycorrhizal presence, and it is well known that recovery efficiencies decline as rates increase. An example of a study actually measuring change in phosphorus uptake caused by mycorrhizae is provided in Table 3 of Grant et al. (2005). Calculations from those data show that the mycorrhizal benefit to phosphorus recovery declining from 69% at low levels of P fertilization to no benefit at very high levels of P fertilization. This is a considerably smaller benefit than is implied by comparing the presented figures of 90% and 15% recovery, and does not take into account the yield losses associated with reduced levels of P fertilization. Second, the implication that plants grown in conventional crop production are without mycorrhizae is incorrect. Mycorrhizae are present in most soils when crops supporting them are grown. These crops include corn, soybeans, wheat and other cereals. Third, studies comparing plants with and without mycorrhizae in the field show much smaller increases in phosphorus uptake, often associated with lower yields. For example, research conducted near Montreal (Liu et al., 2003) showed that corn yield response to the presence of mycorrhizae was small (8%), occurring only when corn was not fertilized with phosphorus, while fertilization with phosphorus produced yield gains of up to 18%. In this experiment, fertilizing at recommended rates reduced mycorrhizal hyphae density by only 11%. Similar mutually beneficial effects of mycorrhizae and phosphorus fertilizer were shown in research conducted in British Columbia (Bittman et al., 2003). In certain low phosphorus soils of Australia, mycorrhizae have been shown to have parasitic activity, reducing the yields of crops (Ryan et al., 2005). The fertilizer industry’s 4R Nutrient Stewardship approach recognizes the value of mycorrhizae in crop production (IPNI, 2012 page 2-7). Applying the right source of phosphorus fertilizers at the right rate, right time and right place is consistent with maintenance of an appropriate level of mycorrhizae in agricultural soils.

We appreciate the recognition of the important role of phosphorus in supporting agricultural production for a future global population of over 9 billion. Industry welcomes discussion of issues associated with phosphorus fertilizer use. Improvements in the sustainability of such agricultural production depend on an accurate public perception of these issues, and thus we encourage Professor Hijri to correct the record on the four important points outlined above.

Bittman, S., C. G. Kowalenko, et al. 2006. Starter phosphorus and broadcast nutrients on corn with contrasting colonization by mycorrhizae. Agron J 98(2):394-401.

Cordell, Dana, Jan-Olof Drangert, and Stuart White. 2009. The story of phosphorus: Global food security and food for thought. Global Environmental Change 19:292–305.

Grant, C., Bittman, S., Montreal, M., Plenchette, C. and Morel, C. 2005. Soil and fertilizer phosphorus: Effects on plant P supply and mycorrhizal development. Can. J. Plant Sci. 85: 3–14.

Hendrix, C.S. 2011. Applying Hubbert curves and linearization to rock phosphate. Working Paper Series. WP 11-18. Peterson Institute for International Economics. Washington, DC. p. 12

IPNI. 2012. 4R Plant Nutrition Manual: A Manual for Improving the Management of Plant Nutrition, Metric Version, (T.W. Bruulsema, P.E. Fixen, G.D. Sulewski, eds.), International Plant Nutrition Institute, Norcross, GA, USA.

Liu, A., Hamel, C., Elmi, A. A., Zhang, T. and Smith, D. L. 2003. Reduction of the available phosphorus pool in field soils growing maize genotypes with extensive mycorrhizal development. Can. J. Plant Sci. 83: 737–744.

Ryan, M. H., A. F. van Herwaarden, et al. 2005. Reduced growth of autumn-sown wheat in a low-P soil is associated with high colonisation by arbuscular mycorrhizal fungi. Plant Soil 270(1-2): 275-286.

Scholz, R. and F.W. Wellmer. 2013. Approaching a dynamic view on the availability of mineral resources: what we may learn from the case of phosphorus? Global Environmental Change. 23:11-27

Sutton et al. 2013. Our Nutrient World: The challenge to produce more food and energy with less pollution.  Global Overview of Nutrient Management. Centre for Ecology and Hydrology, Edinburgh.

Syers, JK, AE Johnston, and D Curtin. 2008. Efficiency of soil and fertilizer phosphorus use. FAO Fertilizer and Plant Nutrition Bulletin 18. Food and Agriculture Organization of the United Nations, Rome, Italy.

USGS. 2013. Mineral commodity summaries. [Online]. Available at
commodity/phosphate_rock/index.html#mcs (verified 19 April 2013).

Van Kauwenbergh, S.J. 2010. World Phosphate Rock Reserves and Resources. IFDC. Muscle Shoals, AL, USA.

Friday, November 1, 2013

The Facts about Phosphate Rock… Are We Running Out?

Most of the phosphate rock that is mined from the earth goes towards making fertilizer for
Phosphorus is a major component of bones and teeth
crop production.  Every cell in plants and animals requires phosphorus to sustain itself and there is no substitute for it in nature.

During the past five years, there were several well-publicized reports suggesting the world phosphate rock supply was rapidly dwindling.  In response, there was widespread concern about whether we were reaching our “peak” supply of phosphate rock and if fertilizer shortages are on the horizon.
Map of world phosphorus resources (IFDC)

Recently updated estimates report that the earth has at least 300 years of years of known phosphate rock reserves (recoverable with current technology) and 1400 years of phosphate rock resources (phosphate rock that may be produced at some time in the future).  These numbers fluctuate somewhat since companies do not intensively explore resources that will only be mined far in the future.

Phosphate fertilizer can be a significant cost for crop production and an important mineral for animals.  However from a global perspective, phosphate is considered as a low-price commodity.  One recent publication estimated that each person consumes an equivalent of 67 lb phosphate rock each year.  This results in an annual consumption of about 9 lb phosphorus per person (or 0.4 oz. daily consumption), which is equivalent to 1.7 cents per day.  

Generalized sedimentary  deposit

Phosphorus atoms do not disappear in a chemical sense, but they can be diluted in soil or water to the point where it is not economical to recover.  Annual phosphorus losses by erosion, manure, and human excrement to the sea roughly balance the phosphorus that is mined, showing that there is substantial room for improvement in efficiency.   Implementing appropriate recovery and recycling of phosphorus from animal manure, crop residue, food waste, and human excreta would make a major step in this direction. 

Efforts to improve phosphorus efficiency and building to the appropriate soil P concentrations  serves to enhance its use.  In developed countries with a history of adequate phosphorus fertilization, the need for high application rates diminishes over time.  This contrasts with the situation in many developing countries where low soil P concentrations still require significant fertilizer inputs to overcome crop deficiencies.

Rock phosphate mining in Florida

Members of the public are encouraged to engage in debate over important issues, but there is a danger that oversimplification leads to incorrect conclusions.  The case of looming P scarcity is an example where insufficient information lead to a wrong conclusion.  The wrong notion still persists that there is an impending shortage phosphorus and that limited fertilizer availability will soon lead to global food insecurity.

There may be a scarcity of many earth minerals some day, but the phosphorus supply will not be a concern for hundreds of years.   However responsible stewardship of rock phosphate resources requires a close examination of improving efficiency throughout the entire process, including mining, fertilizing crops, and implementing strategic waste recovery.
Rock phosphate mining in North Carolina