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ABOUT ME

osunpk

osunpk

Since 2008 I have served as the Precision Nutrient Management Extension Specialist for Oklahoma State University. I work in Wheat, Corn, Sorghum, Cotton, Soybean, Canola, Sweet Sorghum, Sesame, Pasture/Hay. My work focuses on providing information and tools to producers that will lead to improved nutrient management practices and increased profitability of Oklahoma production agriculture

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DAP vs MAP, Source may matter!

Historically the two primary sources of phosphorus have had different homes in Oklahoma. In general terms MAP (11-52-0) sales was focused in Panhandle and  south west, while DAP (18-46-0) dominated the central plains.  Now I see the availability of MAP is increasing in central Oklahoma. For many this is great, with MAP more P can be applied with less material. which can over all reduce the cost per acre. There is a significant amount of good research that documents that source of phosphorus seldom matters. However this said, there is a fairly large subset of the area that needs to watch what they buy and where they apply it.

If you are operating under optimum soil conditions the research shows time and time again source does not matter especially for a starter.  In a recent study just completed by OSU multiple sources (dry, liquid, ortho, poly ect ect) of P were evaluated.  Regardless of source there was no significant difference in yield.  With the exception of the low pH site. The reason DAP was so predominate in central Ok, soil acidity.  See an older blog on Banding P in acidic soils.

Picture1

Figure 1. The cover of an extension brochure distributed in Oklahoma during the 1980s.

When DAP is applied, the soil solution pH surrounding the granule will be alkaline with a pH of 7.8-8.2. This is a two fold win on soil acidity aka aluminum (Al) toxicity.  The increase in pH around the prill reduces Al content and extends the life of P, and as the pH comes back down the P ties up Al and allows the plant to keep going. However, the initial pH around the MAP granule ranges from an acid pH of 3.5-4.2.  There is short term  pH change in the opposite direction of DAP, however the the Al right around the prill becomes more available and in theory ties up P even faster.

Below is a table showing the yield, relative to untreated check, of in-furrow DAP and MAP treatments in winter wheat.  The N401 location had a ph 6.1  while Perk (green) has a pH of 4.8.  At Perkins in the low pH, both forms of P significantly increased yeild, almost 20 bushel on the average.  DAP however was 5 bushel per acre better than MAP. At the N40 site the yield difference between the two sources was 1 bushel.

MAPvDAP2

Relative yield winter wheat grain yield MAP and DAP both applied at equal rates of P (32 lbs P2O5 ac) when compared to a untreated check.

In general it can be said that in acid soils DAP will out preform MAP while in calcareous high pH soils MAP can out preform DAP. So regarding the earlier statement about the traditional sales area of MAP or DAP if you look at the soil pH of samples went into the Oklahoma State University Soil, Water, and Forage Analytical lab the distribution makes since.

State pH

Average soil pH of samples sent into OSU soil water forage analytical lab by county.

In the end game price point and accessibility drives the system.  In soils with adequate soil pH levels, from about 5.7 to around 7.0, get the source which is cheapest per lbs of nutrient delivered and easiest to work with. But if you are banding phosphorus in row with your wheat crop because you have soil acidity, DAP should be your primary source.

Canola fertilizer rates when skip row seeding.

When drilling canola a common strategy to improve seeding rate accuracy is to only use every other row which effectively doubles the rate of seed going through each meter.  There are also many producers who utilize air seeders and just prefer the wider spacing.  Every season I get several questions about determining total fertilizer rates if the seed is dropped every other row but fertilizer is dropped every row. Regardless of whether or not fertilizer goes down every row it is important that the amount of salts placed with seed does not exceed the limit.  The table below provide the limits in terms of lbs of salt per acre.  If using 18-46-0 (DAP) or 11-52-0 (MAP) this is equivalent to pounds of N per acre. However if the fertilizer you use contains potassium (K) or sulfur (S), those have to be considered. An easy rule of thumb for determining total salt level of a fertilizer is pounds of N + K + 1/2 S.

Maximum amount of salt that can be applied in furrow with canola seed. Application rate should be at or below this value.

Maximum amount of salt that can be applied in furrow with canola seed. Application rate should be at or below this value.

In a scenario in which canola is seeded in skip rows but every row will get fertilizer the total amount of fertilizer can be doubled.  For example on a 15″ row spacing the max salt rate is 5 lbs per acre. If you were using DAP as your starter that maximum rate to place in furrow would be 28 lbs of DAP per acre.  If using a drill set of 7.5″ spacing and putting fertilizer down every row the max rate would increase up to 56 lbs DAP per acre.

 

Seed, colored blue, is placed in every other row but an equal amount of fertilizer, dark grey circles, is placed in every row.

Seed, colored blue, is placed in every other row while an equal amount of fertilizer, dark grey circles, is placed in every row.

Some producers may have the capability of applying different rate in every other row.  In this scenario it is important to maintain that safe rate in the seed furrow. In the opposite row, fertilizer rate can go as high as you wish or the equipment can handle.

Seed, colored blue, is placed in every other row but an fertilizer, dark grey circles, is placed in every row. In this scenario a high rate is placed in the row without seed.

Seed, colored blue, is placed in every other row  while fertilizer, dark grey circles, is placed in every row. In this scenario a high rate is placed in the row without seed.

Now the big question is, “Is between row fertilization a good idea?” While we do not have results on this style of application (trials will be going out this year)  we can draw upon upon similar work in other crops. For me the best win would be the second scenario in which a higher rate could be place between the rows.  In this row I would use a urea and DAP blend.  Any time we can put urea below the soil surface its a win and in fields with very soil soil test phosphorus (P) it would create something similar to the deep P bands  once popular in corn production. Now if the field had adequate soil test P, I would focus on urea between rows. Keep in mind it is never a good to place urea in furrow with canola seed. For the average producer who is using a box drill the first scenario is the only option.  In this case the rate of the between row bands will be reduced however I still believe on fields with very low soil test P this is potentially a great way to get the rest of it on. Remember if on 15″ and using DAP max rate only gets 12.9 lbs of P2O5 down.  If fertilizer is dropped down every tube that number increases to about 26 lbs P2O5, which is still not enough for fields with low soil test P, but is better.  With hope we will have some good results to share from the 2015-2016 canola crop.

Phosphorus Fertilizer recommendations based upon Mehlich 3 P test reported as STP index (ppm * 2)

Phosphorus fertilizer recommendations based upon Mehlich 3 P test, reported as STP index (ppm * 2)

 

Nutrient Products: Stabilizers, Enhancers, Safeners, Biologicals and so on.

In this blog I am not going to tell you what to use or what not to use. In fact I will not mention a single product name. What I will do is hopefully provide some food for thought, new knowledge and direction.

First I want to approach a topic I have been called out on several times. I believe there is a stigma that University researchers and extension specialists do not want products to work.  It may seem that way at times but it is far from the truth. The reality is that all of us are scientists and know someone may be inventing the product that changes nutrient management as we speak.  The issue is that most of us have been jaded. While I may be younger I have over 11 years experience, testing “products” in the field, and that includes dozens of products. I have sprayed, spread, tossed, drilled, mixed and applied everything under the sun, with  hopes that I will see that one thing I am always looking for, MORE GRAIN…

The truth is Everything works Sometimes yet Nothing works ALL the time. I and others in my profession do not expect anything to work 100% of the time, I am personally looking for something that will provide a checkmark in the win column 50% of the time. A win is the result of one of two things, more money in the producers pocket or less nutrients in the water or air.  Products can increase vigor, nutrient uptake, chlorophyll concentration, greenness but not yield. What Co-op or elevator pays for any of those attributes?  Grain makes green.

 

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So many safeners, stabilizers, enhancers, biologicals, and on and on are available, so what should a producer do?  Here are few things to think about. Ask yourself “ what part of my nutrient management plan can I get the most bang from improving”?

If the answer is Nitrogen (N) there are three basic categories: Urease inhibition, Nitrification inhibitor, and slow release. All are methods of preventing loss; the last two are preventing loss from water movement.

Urease inhibitors prevent the conversion of Urea to NH3 (ammonia). This conversion is typically a good thing, unless it happens out in the open.  Ideally any urea containing product is incorporated with tillage or rain. However, in No-till when urea is broadcast and no significant rainfall events (>0.5”) occur, N loss is likely. The urea prill starts dissolving in the presence of moisture, this can be a light rain or dew, and urease starts converting urea into NH3. As the system dries and the day warms, if there was not enough moisture to move the NH3 into the soil the wind will drive NH3 into the atmosphere. Nitrogen loss via this pathway can range from 5% to 40% of the total N applied.

 

Graphic of Urea's conversion to plant available ammonium.

Graphic of Urea’s conversion to plant available ammonium.

Wet Soil

Urea placed on a wet soil under two different temperatures. Number in white is hours after application.

Dry Soil

Urea placed on a dry soil, on top no water added, bottom left is moisture from the subsurface, and bottom right is simulated rain fall of 1/2″. Number in white is hours after application.

 

 

 

 

 

 

 

 

 

 

 

Nitrification inhibitors prevent the conversion of NH4 into NO3.  Both are plant available N sources but NH4 is a positively charged compound that will form a bound with the negatively charged soil particles.  Nitrate (NO3) is negatively charged and will flow with the water, in corn country that tends to be right down the tile drainage.  Nitrate will also be converted to gasses under wet water logged soil conditions. Nitrate is lost in the presence of water, this means I do not typically recommend nitrification inhibitors for western OK, KS, TX dryland wheat producers.

Slow release N (SRN) comes in a range of forms: coated, long chain polymer, organic and many versions in each category.   Again, water is the reason for the use of SRN sources. Slow release N whether coated or other have specific release patterns which are controlled by moisture, temperature and sometimes microbes.  The release patterns of SRNS are not the same and may not work across crops and landscapes. For instance in Oklahoma the uptake pattern of nutrients for dryland corn in the North East is not that same as irrigated corn in the West. The little nuances in the growth pattern of a crop can make or break your SRN.

While N products have been on the market for decade’s phosphorus enhancers and stabilizers are relatively new, resulting in many of my peers holding back on providing recommendations until field trials could be conducted. At this point many of us do have a better understanding of what’s available and are able to provide our regional recommendations.  Phosphorus products are not sold to prevent loss like their N counterparts; they are sold to make the applied P more available. On a scale of 1 to 10, P reactivity with other elements in the soil is a 9.9.  If there is available Ca, Mg, Fe, or Al, phosphorus is reacting with it.  In the southern Great Plains it is not uncommon for a soil to have 3,000-5,000 lbs of available Ca, a soil with a pH of 4, yes we have many of those, will have approximately 64,000 lbs of Al in the soil solution.  That’s a lot of competition for your fertilizer P and for any substance that is trying to protect it.

I have been testing “biologicals” of all shapes and forms since 2003.  While I have not hit any homeruns I have learned quite a bit.  Many of these products originate from up north where the weather is kind and organic matter (OM) is high.  Where I work the average OM is 0.75% and soil temp is brutal and unforgiving.  Our soil does not have many reserves to release nor is it hospitable to foreign bodies.

Soil temperature for Stillwater OK under sod and bare soil conditions.  Graph from www.Mesonet.org.

Soil temperature for Stillwater OK under sod and bare soil conditions. Graph from http://www.Mesonet.org.

I hope you are still hanging on as this next topic is a bit of a soap box for me.  Rate, Rate, Rate this aspect is missed both by producers and academia and it drives me crazy.  If your crop is sufficient in any growth factor adding more will not increase yield.  It goes back to Von Liebig’s LAW of the Minimum.  I see too many research studies in which products are tested at optimum fertilization levels.  This is just not a fair comparison.  On the other hand, time and again I see producers sold on a product because they applied 30% less N or P and cut the same yield.  If you let me hand pick 100 farms in Oklahoma I could reduce the N rate by 30% of the average and not lose a bushel on 75 of the farms.  Why? Because the rate being used was above optimum in the first place, there is no magic just good agronomy.  The list of products that increase the availability of nutrients is a mile long. Increasing nutrient availability is all well and good if you have a deficiency of one of those nutrients.  If you don’t, well you have increased the availability of something you did not need in the first place.

University researchers and extension professionals seem to live and die by the statistics, and are told so regularly. We do rely upon the significant differences, LSD’s, and etc to help us understand the likely hood of a treatment causing an effect.    However if I see a trend develop, or not develop, over time and landscape regardless of stats I will have no problem making recommendations.    The stats help me when I do not have enough information (replications).

Too wrap up, have a goal.  Do not just buy a product because of advertised promises or because a friend sells it.  There is a right time and place for most of the things out there, but you need to know what that is and if it suits your needs.  I also recommend turning to your local Extension office.  We do our best to provide unbiased information in hopes of making your operation as sustainable as possible.  If you are looking at making sizable investments do some reading, more than just Google.  Testimonies are great but should but should not be enough to cut a check. Google Scholar www.google.com/scholar is a good resource for scientific pubs.  I have done my best to put together a list of peer reviewed publications and their outcomes.  To make the review work I had to be very general about outcome of the research.  Either the product increased yield or decreased environmental losses or it had no impact.   This was not easy as many of the papers summarize multiple studies.  I did my best to make an unbiased recommendation but some could be argued.    http://npk.okstate.edu/Trials/products/Product_Peer_Review.8-21-2014.pdf

 

Banding P as a Band-Aid for low-pH soils.

In the mid-1970s Dr. Robert Westerman banded 18-46-0 with wheat at planting in a low-pH soil near Haskel Ok. The impact was immediately evident. Soon after Oklahoma State University recommended the “Banding of Phosphate in Wheat: A Temporary Alternative to Liming” Figure 1. This method was a Band-Aid solution for the significant amount Oklahoma winter wheat production area which was either too far from a reliable lime source or under a short term lease contract.

Figure 1. The cover of an extension brochure distributed in Oklahoma during the 1980s.

Figure 1. The cover of an extension brochure distributed in Oklahoma during the 1980s.

Still today grain producers throughout the United States commonly farm a large percentage of land that is not their own. In the leasing process agreements can widely vary both on length of the lease and the amount of inputs that the land owner will pay. The wheat belt of Oklahoma is known for having large areas with low soil pH levels. A survey of soil samples submitted to the Oklahoma State University Soil, Water, and Forage Analytical Laboratory in 2011 under the winter wheat crop code showed 38% of the samples having a soil pH level below 5.5 (Figure 2). In Oklahoma short term leases with limited shared expenses have limited the access to agricultural lime for remediation of acidic soils. In the dry environment it may take up to one year before the lime applied has completely corrected the soil acidity problem. In a situation where the lease agreement is only for one to two years there may be no economic benefit for the producer to apply lime especially in regions where winter wheat average yields range from 20 to 40 bushel per acre. The current recommendation for winter wheat producers working on low-pH short term lease ground is to apply 30 lbs P2O5 ac-1 ( 65 lbs 18-46-0 ac-1) with the seed for grain only wheat and 60 lbs P2O5 ac-1 (130 lbs 18-46-0 ac-1) for dual-purpose wheat production. This recommendation however is for soils with adequate soil test P, but low soil pH. When soil test P is below optimum the 30 or 60 units is applied in addition to the amount needed to reach 100% sufficiency.
Banding P is considered a “Band-Aid” as the problem of soil acidity is not re-mediated it is only masked.  If not addressed the pH of the soil will continue to fall over time.  Aluminum and manganese toxicity is the greatest issue associated with soil acidity. Available aluminum, a predominant mineral in the regions soils, is pH dependent. A change of 1.0 pH level changes available Al by 1000 fold. For example a soil with a pH of 5.0 will have an approximate Al concentration of 27 ppm, critical level of winter wheat is 27 ppm, while a soil with a pH of 4.0 will have an Al concentration of approximately 27,000 ppm. Aluminum and manganese toxicity does not only impact grain yield but it has an even greater impact on biomass production. Kariuki et al (2007) recorded the impact of soil acidity on eight current winter wheat lines. Correcting soil acidity increased wheat grain yield by 82% and increased forage production by 150%. For Oklahoma the forage produced by the wheat crop is as important as the grain. Oklahoma is unique in that approximately 50% of the four million acres of winter wheat are grazed annually much of this under the dual –purpose “Graze-N-Grain” management. To maintain productivity on the land without the long term investment of Ag lime producers have been applying phosphorus fertilizer to alleviate the impact of aluminum toxicity.

Figure  2.  Summary of the soil pH values for the 614 samples submitted to the Oklahoma State University Soil, Water, Forage, Analytical Laboratory under wheat crop code during the time frame of 1-1-2011 11-30-2011.

Figure 2. Summary of the soil pH values for the 614 samples submitted to the Oklahoma State University Soil, Water, Forage, Analytical Laboratory under wheat crop code during the time frame of 1-1-2011 11-30-2011.

In 1992 Boman et al reported that impact banding phosphates with seed on winter wheat forage production (Figure 3). Across the four locations the addition of P increase yield from 2 to 4 fold. The work by Kaitibie et al (2002) documented an additional aspect of banding P. In the variable and often arid climate of Oklahoma the activation of lime can take a significant amount of time, in upwards of one year. In comparison banding P has an immediate impact on the alleviation of metal toxicities. Figure 4 shows the incorporation of lime improved forage yield but not to the degree of banding P. For continuous winter wheat producers the time between application of lime and planting can be quite short. Typically the previous crop will be harvest in mid-June and in the best case scenario lime would be applied and incorporated by mid-July. At this point there is only 60 days until the next wheat crop is planted in early to mid-September.

Figure 3.  The impact of banding phosphate with seed at planting in acidic soils on winter wheat forage production in Oklahoma.  Chart adapted from Boman et al. 1992.

Figure 3. The impact of banding phosphate with seed at planting in acidic soils on winter wheat forage production in Oklahoma. Chart adapted from Boman et al. 1992.

Figure 4.  The impact of applying of phosphate fertilizer and lime on the forage production of two winter wheat cultivars in Oklahoma.  Chart adapted from Kaitibie et al. 2002.

Figure 4. The impact of applying of phosphate fertilizer and lime on the forage production of two winter wheat cultivars in Oklahoma. Chart adapted from Kaitibie et al. 2002.

For many with short term leases banding P is still the only viable solution for wheat production in low-pH soils. However there is ground being farmed by the owner or is under long-term lease that is still receiving this Band-Aid approach. At the 1980-1990 fertilizer and lime prices there is good reason to continue this method. However the cost of P fertilizer has quadrupled since the 1970’s. The last ten year average price of P2O5 was $0.42 per pound while it cost an average of $0.10 in the 70s.  So for those who own or are able to work out beneficial lease agreements Table 1 should be of interest. By year three the cost of phosphate exceeds the cost of lime. If you were to use the values from the 1980’s of $0.20 per pound of P2O5 and $25 per ton ECCE lime it was not until year five, the last year before reapplying lime, did the cost of P exceed cost of lime.

Table 1.  Cumulative cost per acre of applying phosphorus and lime to remediate aluminum and manganese toxicity based on a five year liming cycle. The 30 lb P2O5 rate is recommended for grain only production while dual-purpose wheat require 60 P2O5.  Prices based on current quotes of DAP at $590 a ton ($0.41 lb P2O5) and Ag lime at $30 per ton ECCE.

Table 1. Cumulative cost per acre of applying phosphorus and lime to remediate aluminum and manganese toxicity based on a five year liming cycle. The 30 lb P2O5 rate is recommended for grain only production while dual-purpose wheat require 60 P2O5. Prices based on current quotes of DAP at $590 a ton ($0.41 lb P2O5) and Ag lime at $30 per ton ECCE.

As the 2014 winter wheat and canola crop is being transported to the bins it is extremely important to take advantage of this time to take soil samples from as many fields as possible. Soil pH issues must be understood and addressed. I often remind producers soil pH plays an exception number of roles. Not only does it impact yield as shown before but it impacts rooting (ability to survive stresses), nutrient availability, and herbicide activity. Our SU herbicides (Finesse, Powerflex, and Maverick) that are used widely across the state are negatively impacted by low soil pH. Figure 5 shows how at a pH of 5.6 Glean is down to a 50% concentration in the soil approximately two weeks after application. So when it comes time to make the call for phosphorus or lime try to weigh all of these aspects, at current prices P is not that much cheaper, improving pH will improve yield and potentially improve weed control.

Figure 5. The concentration of Glean (Cholorsulfuron) remaining in too soils (pH 7.5 and pH 5.6) over a twelve week period.

Figure 5. The concentration of Glean (Cholorsulfuron) remaining in too soils (pH 7.5 and pH 5.6) over a twelve week period.

Citations

Boman,R.K., R.L. Westerman, G.V. Johnson, and M.E. Jojola.  1992. Phosphorus fertilization effects on winter wheat production in acid soils. In Soil Fertility Highlights, Agronomy Department Oklahoma Agricultural Experiment Station, Oklahoma State University.Agronomy 92-1 pg171-174

Kaitibie,S., F. M. Epplin, E.G. Krenzer, and H. Zhang. 2002. Economics of lime and phosphorus application for dual-purpose wheat production in low-pH soils.  Agron. J. 94:1139:1145.

Kariuki, S.K., H. Zhang, J.L. Schroder, J. Edwards, M. Payton, B.F. Carver, W.R. Raun, and E.G. Krenzer.   2007. Hard red winter wheat cultivar responses to a pH and aluminum concentration gradient. Agron J. 99:88-98.