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Which fertilizer? MAP or DAP?
7 June 2011 | Categories: MAP, DAP, phosphorus, fertiliser, phosphate
The relative merits of different phosphorus fertilizers for crops can be easily misunderstood. Most confusion surrounds monoammonium phosphate (MAP) and diammonium phosphate (DAP), especially when technical information is used to promote one of these fertilizers over the other.
Sales pitches of the benefits of MAP and DAP tend to focus on their different pH of dissolutions. pH of dissolution refers to the pH of the solution in and immediately around fertilizer granules. The pH (water) of dissolutions for MAP and DAP are approximately 4 to 5 and 7 to 8 respectively (http://frec.cropsci.illinois.edu/1990/report7/index.htm).
Any theoretical benefits of MAP or DAP based on different pH of dissolution are rarely transferred to consistent performance in the field. At best, only small differences in phosphorus efficiency have been measured across most experimental conditions and crops. The exception is highly calcareous soils where it is now widely recognized that acidic phosphorus sources from MAP generally out performs phosphorus from DAP .
In the field it tends to be other differences in chemical and physical properties that determine whether MAP or DAP produces the better plant response in any given set of conditions. The key property differences are:
- nitrogen content: usually 10 to 11% for MAP and 18% for DAP.
- salt index: compares the increase in osmotic potential brought about by addition of a fertilizer compared to the increase when an equivalent weight of sodium nitrate is added to water. Depending on source, the salt index for MAP is normally about 30 and DAP is more salty at about 34 but at similar product rates the difference is negligible.
- potential to cause ammonia toxicity: primarily related to ammonium concentration, pH of the reaction product with the soil solution and product solubility. High ammonium concentration, high pH and high product solubility can all create conditions in the area of application that are favorable for the generation and maintenance of concentrations of ammonia that are toxic to germinating seeds.
- product solubility: an important characteristic, not only in relation to nutrient availability to plants, but also on the rate of chemical reactions that can be detrimental to plants. Higher solubility increases salt index and potential for ammonia toxicity. The solubility (at 20oC) of MAP is approximately 35 to 40 kg/100L while DAP is 65 to 70 kg/100L (National Fertiliser Solutions Association: Liquids Manual 1986)
Differences between MAP and DAP are smallest and mostly nonexistent when the fertilizers are broadcast and incorporated into the soil, and when they are drilled preplanting into neutral to acid soils. However because DAP contains about twice as much ammonium-nitrogen as MAP, and because its pH of dissolution is more alkaline than MAP, DAP has greater potential for nitrogen loss through ammonia volatilization when broadcast onto neutral to alkaline soils. Nitrogen losses from DAP can be 0 – 20% higher than MAP when broadcast on neutral to alkaline soils.
Differences in the key properties listed above are much more important when MAP and DAP are applied with or near the seed, or in close contact with living plants.
Applied at the same rate, DAP is more likely than MAP to reduce germination and restrict root growth through ammonia toxicity because of its higher potential to release free ammonia. In laboratory conditions, release of free ammonia from DAP has been measured as 300% higher than from MAP.
The decision on whether to drill MAP or DAP with or near seed is largely determined by the likelihood of crop establishment damage, which in turn is influenced by crop susceptibility and type and setup of application equipment. Crops like canola, soybean and linseed are more sensitive to establishment damage that is more likely with DAP than MAP. Changes to application equipment, like wider row spacing and narrower tines, will exacerbate any establishment problems caused by fertilizer. In this case professional advise should be sought to ascertain whether current rates are appropriate for the new sowing equipment.
Trace elements are sometimes included in or on granules during manufacture of MAP and DAP so the fertilizers can be carriers for the trace elements and even to differentiate otherwise fairly generic products. Research suggests that trace elements are likely to be more effective in MAP based fertilizers than DAP based fertilizers, and that for the best response to trace elements in the year of application, water solubility of trace elements in compounded products should be at least 40%.
In summary, there is little agronomic difference between MAP and DAP as sources of phosphorus. However caution should be exercised when using DAP under some soil and environmental conditions to avoid establishment damage.
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📷📷Home > News > Which fertilizer? MAP or DAP? 12
Subscribe
News Archive
- 2017,
- 2016,
- 2015,
- 2014,
- 2013,
- 2012,
- 2011
Facebook Twitter Print Email Addthis 100Share var _gaq = _gaq || []; _gaq.push(['_setAccount', 'UA-7136207-1']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })();
News
Which fertilizer? MAP or DAP?
7 June 2011 | Categories: MAP, DAP, phosphorus, fertiliser, phosphate
The relative merits of different phosphorus fertilizers for crops can be easily misunderstood. Most confusion surrounds monoammonium phosphate (MAP) and diammonium phosphate (DAP), especially when technical information is used to promote one of these fertilizers over the other.
Sales pitches of the benefits of MAP and DAP tend to focus on their different pH of dissolutions. pH of dissolution refers to the pH of the solution in and immediately around fertilizer granules. The pH (water) of dissolutions for MAP and DAP are approximately 4 to 5 and 7 to 8 respectively (http://frec.cropsci.illinois.edu/1990/report7/index.htm).
Any theoretical benefits of MAP or DAP based on different pH of dissolution are rarely transferred to consistent performance in the field. At best, only small differences in phosphorus efficiency have been measured across most experimental conditions and crops. The exception is highly calcareous soils where it is now widely recognized that acidic phosphorus sources from MAP generally out performs phosphorus from DAP .
In the field it tends to be other differences in chemical and physical properties that determine whether MAP or DAP produces the better plant response in any given set of conditions. The key property differences are:
- nitrogen content: usually 10 to 11% for MAP and 18% for DAP.
- salt index: compares the increase in osmotic potential brought about by addition of a fertilizer compared to the increase when an equivalent weight of sodium nitrate is added to water. Depending on source, the salt index for MAP is normally about 30 and DAP is more salty at about 34 but at similar product rates the difference is negligible.
- potential to cause ammonia toxicity: primarily related to ammonium concentration, pH of the reaction product with the soil solution and product solubility. High ammonium concentration, high pH and high product solubility can all create conditions in the area of application that are favorable for the generation and maintenance of concentrations of ammonia that are toxic to germinating seeds.
- product solubility: an important characteristic, not only in relation to nutrient availability to plants, but also on the rate of chemical reactions that can be detrimental to plants. Higher solubility increases salt index and potential for ammonia toxicity. The solubility (at 20oC) of MAP is approximately 35 to 40 kg/100L while DAP is 65 to 70 kg/100L (National Fertiliser Solutions Association: Liquids Manual 1986)
Differences between MAP and DAP are smallest and mostly nonexistent when the fertilizers are broadcast and incorporated into the soil, and when they are drilled preplanting into neutral to acid soils. However because DAP contains about twice as much ammonium-nitrogen as MAP, and because its pH of dissolution is more alkaline than MAP, DAP has greater potential for nitrogen loss through ammonia volatilization when broadcast onto neutral to alkaline soils. Nitrogen losses from DAP can be 0 – 20% higher than MAP when broadcast on neutral to alkaline soils.
Differences in the key properties listed above are much more important when MAP and DAP are applied with or near the seed, or in close contact with living plants.
Applied at the same rate, DAP is more likely than MAP to reduce germination and restrict root growth through ammonia toxicity because of its higher potential to release free ammonia. In laboratory conditions, release of free ammonia from DAP has been measured as 300% higher than from MAP.
The decision on whether to drill MAP or DAP with or near seed is largely determined by the likelihood of crop establishment damage, which in turn is influenced by crop susceptibility and type and setup of application equipment. Crops like canola, soybean and linseed are more sensitive to establishment damage that is more likely with DAP than MAP. Changes to application equipment, like wider row spacing and narrower tines, will exacerbate any establishment problems caused by fertilizer. In this case professional advise should be sought to ascertain whether current rates are appropriate for the new sowing equipment.
Trace elements are sometimes included in or on granules during manufacture of MAP and DAP so the fertilizers can be carriers for the trace elements and even to differentiate otherwise fairly generic products. Research suggests that trace elements are likely to be more effective in MAP based fertilizers than DAP based fertilizers, and that for the best response to trace elements in the year of application, water solubility of trace elements in compounded products should be at least 40%.
In summary, there is little agronomic difference between MAP and DAP as sources of phosphorus. However caution should be exercised when using DAP under some soil and environmental conditions to avoid establishment damage.
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Dear you will find the answer in this paper:
Optimizing Available Phosphorus in Calcareous Soils
Fertilized with Diammonium Phosphate and Phosphoric Acid
Using Freundlich Adsorption Isotherm.
I agree with Benhmimou. Look at that paper.
Article Optimizing Available Phosphorus in Calcareous Soils Fertiliz...
Phosphorus (P) is an essential element classified as a macronutrient because of the relatively large amounts of P required by plants. Phosphorus is one of the three nutrients generally added to soil as fertilizer. One of the main roles of P in living organisms is in the transfer of energy. Organic compounds that contain P are used to transfer energy from one reaction to drive another reaction within cells. Adequate P availability for plants stimulates early plant growth and hastens maturity.
Although P is essential for plant growth, mismanagement of soil P can pose a threat to water quality. The concentration of P is usually sufficiently low in fresh water so that algae growth is limited. When lakes and rivers receive amounts of P that exceed their background levels, excessive growth of algae often occurs. Increased levels of algae reduce water clarity and can lead to decreases in available dissolved oxygen as the algae decay. These conditions can be very detrimental too much of the aquatic life and can limit the recreational use of lakes such as game fishing and other water activities.
Forms of phosphorus in soils
In soils, P exists in many different forms. In practical terms, however, P in soils can be thought of existing in three pools:
- The solution P pool: This pool is very small and usually contains less than a pound of P per acre. It is mostly inorganic P. Plants take up P primarily in the orthophosphate form. Solution P is important because it is the pool from which plants take up P and is the only pool that has any measurable mobility.
- The active P pool: The active pool is P in the solid phase that is more readily released to the soil solution, the water surrounding soil particles. As plants take up phosphate, the concentration of phosphate in the solution is decreased and some phosphate from the active P pool is released. This is the main source of P available for crops. The active P pool will contain inorganic phosphate that is attached to small particles in the soil, phosphate that reacted with elements such as calcium or aluminum to form somewhat soluble solids, and organic P that is easily mineralized.
- The fixed P pool: This pool of phosphate will contain inorganic phosphate compounds that are very insoluble and organic compounds that are resistant to mineralization by soil microorganisms. Phosphate in this pool may remain in soils for years without being made available to plants and may have very little impact on the fertility of a soil.
Fate of phosphorus added to soils
The phosphate in fertilizers and manure is initially quite soluble and available. Most phosphate fertilizers have been manufactured by treating rock phosphate with acid to make it more soluble. Manure contains soluble, organic, and inorganic phosphate compounds that are highly available. When fertilizer or manure phosphate contacts soil, various reactions begin occurring that make the phosphate less soluble and less available. The rates and products of these reactions depend on such soil conditions as pH, clay content and type of clay, moisture content, temperature, and the P minerals already present in the soil.
Predicting the availability of phosphorus in soils
To determine the need for supplemental P, soil tests are often used to estimate how much phosphate will be available for a crop. The two most common types of soil tests in Minnesota are the Bray-1 and the Olsen test. Researchers have calibrated the Bray-1 P soil test for acidic soils and is the preferred test when soil pH is less than or equal to 7.4. The Olsen test is used when the pH of a soil samples is 7.4 or greater.
Soil tests like the Bray-1 P and the Olsen are an availability index, which have the goal of estimating the amount of P from both the solution and active pools that the plant can use. Calibration studies have been done to correlate crop response to fertilizer additions in soils with various soil test levels of P. Using the calibration data, recommendations can be made as to the amounts of phosphate fertilizer that will most likely give optimum yields.
Soil phosphorus and water quality
Phosphorus is a somewhat unique pollutant in that it is an essential element, has low solubility, and is not toxic itself, but may have detrimental effects on water quality at quite low concentrations. Phosphorus is typically the limiting nutrient for algal growth in freshwater ecosystems. The addition of P to freshwater increases algal growth. When algae die and begin to decompose, anoxic conditions are created as O2 is depleted from the water, a process called eutrophication. Because of eutrophication, there is considerable concern about P being lost from soils and transported to nearby streams and lakes. Several chemical properties of soil P have important implications for the potential loss of P to surface water.
Phosphate in soils is associated more with fine particles than coarse particles. When soil erosion occurs, more fine particles are removed than coarse particles, causing sediment leaving the soil through erosion to be enriched in P. When those soil particles are carried to a river or lake, P will be contained in this sediment.
In instances when sediment is a source of P to the water, eutrophication can potentially impair the water system. Therefore, responsible P management in agricultural and industrial systems should be sought to reduce potential negative impacts on the environment.
Overall the fertilizer having maximum residual acidity shall be best for alkaline /calcareous soils.
Are you sure you need to add Phosphorus to your soil ?
If you have not done so yet, check if you soil is alive. If it is, chances are you don't need any, no matter what you grow on it. If it is not, seek how to make it alive. Then ask your self if you need additional P.
It is not good to use SSP or TSP in alkaline soil with high clay content. It is better to apply MAP or DAP in such soils.
Please find enclosed some reference papers, which may be useful to arrive at a decision
En general, el fertilizante con una acidez residual máxima será mejor para los suelos alcalinos.
The issue with alkaline soil and Phosphorus is that Calcium in solution under these conditions precipitates the Phosphorus making it unavailable. Under this condition Zinc deficiency is also common. For field crops such as maize the most efficient use of fertilizer is the use starter fertilizer focused on Phosphorus. If a band of fertilizer is applied 3 to 4 cm to the side of the planting row and 3 to 4 cm below the seed depth the fertilizer can optimize the growth of the germinating seeds without suffering for excess of salts. For your environment I would suggest using Diammonium Phosphate DAP which is mixed with granular humate. These should be mixed at equal weights and applied at 200 kg/ha this should give 9 nitrogen and 20 phosphate for starter. When your maize would be about knee high the application of 80 to 120 Kg N as urea or ammonium sulfate would give very aggressive growth and high productivity. If you find Zinc chlorosis the use of foliar Zinc sulfate with urea is ever effective. If you do zinc foliar your optimized level should be superior to 40 ppm.
Humate helps to mobilize Phosphate in all soils but particularly in low organic matter soils.
Nice information by Hepperly. My experience says in acidic soil broadcasting of rock phosphate is an economically efficient source. For normal soils and even in alkaline soil, band placement of DAP or MOP is ideal source. Subhan Danish experienced hardness in soil after application of DAP. What may be the possible reason.
Band application near the seed zone reduces the percentage of P fixed and the placement increases the efficiency of access in the critical seedling stage stimulating an aggressive root system. The fixation of P can reach 80% in some cases the use of organic matter increases the P efficiency by increasing P availability which people believe is related. The hydroscopic nature of the fertilizer might be a mechanism for hardening the soil area. I think the humates in fertilizer would help that condition but you have to check it out to tell for sure. Humates are known to aid salinity issues related with fertilizer use many alkaline soils are also dealing with salt issues.
Then, soil hardening issue with P fertilizer may be addressed through organic amendment and water management.
Do not apply any Phosphorus of these kind. They will ruin the life of your soil (fungi communities). Ask yourself the question why you would apply phosphorus first. You will save a bunch of money and you will save your soil. If you need help contact me.
DAP is better in calcareous soil but Urea phosphate is the best because of acid pH which is better in calcareous soil
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