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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 in short supply? Revisiting, DAP vs MAP, Source may matter!

From mid August through October, fertilizer applicators and grain drills are running across the southern great plains wheat ground. Di-ammonium Phosphate (DAP 18-46-0) is maybe the most popular form of phosphorous (P) utilized in wheat production today. DAP delivers a high content of nitrogen (N) while efficiently binding the toxic aluminum (Al) ions low pH soils. However due to the flooding that occurred throughout the spring the Ports have been closed and DAP could be in short supply. I have heard that many companies and Co-ops have already sourced Mono-ammonium phosphate (MAP 11-52-0) to supplement the lack of DAP for our early planted wheat crop. With this happening, I wanted to share some points about the two sources. In a broadcast incorporated scenario I do not have much preference for one over the other. It is when producers are applying the fertilizer in-furrow or applying to alleviate Al toxicity that source can matter. As described in the post below, in a soil with a neutral pH DAP and MAP perform equally well. So in this scenario I give MAP a slight edge over DAP if the price is the same. I say this as you can run less material per acre with MAP and refill a little less often. Many worry about the drop in N delivered with MAP versus DAP but in my work I see that is the P in the starter that gives us a good response and not the N, which can be delivered with pre-plant or top-dress. However, DAP wins out in soils with a pH below 5.5. The original blog below shows the results when DAP and MAP are banded in acidic soils using the same rate of P per acre.  The reason we see this happen is that when MAP dissolves it forms a slightly acidic solution (approx 4.0) while DAP will dissolve to form a slightly basic solution (approx 7.5). In our work BOTH DAP and MAP increased yield above the check in acidic soils, which goes to show MAP is an affect tool for short term remediation of aluminium toxicity (Band P for Al toxicity Blog). However it might require more MAP per acre to reach the equivalent results. Because of what we saw when comparing the two sources at equivalent rates of P, I would recommend increasing the rate of P2O5 from 30 lbs per acre to 35 or 40. This would be going from 65 lbs of DAP to 67-77 lbs of MAP per acre.

So the take home would be as this wheat season takes off and you find that DAP is hard to locate and you A) Have overall neutral (5.5+) pH levels do not hesitate using MAP. Run the normal amount of material getting a few extra lbs of P or apply less material to get the same amount of phosphate. B) Have a acidic situation and are banding to alleviate aluminum toxicity use the same amount of material or a little bit more.  Keep in mind in acidic soils with a low soil test P level you have to apply enough phosphate to take care of the Al and enough to take care of the P deficiency. Note the results of the NPKS wheat response strip (NPKS BLOG)

Original Post Published July 18, 2016
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 yield, 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.

Double Crop Response to Additional N, P, K and S.

Vaughn Reed, PhD. Student Precision Nutrient Management
Brain Arnall Precision Nutrient Management Extension Specialist.

Data presented below are the results of Mr. Reeds Masters research project.

On farm research trials are important, because they give us the ability to see responses over a larger geographic area, and even more importantly, evaluate our recommendations on fields that are managed by producers, not researchers.  They also allow us to look at current production practices and see if there are any missed opportunities. Several years ago, we looked at whether producers were leaving yield on the table by not applying enough nitrogen (N), phosphorus (P), potassium(K), and sulfur (S) to winter wheat. We did this by applying strips of N, P, K, and S fertilizer on farmers’ fields with the instructions to not change their fertilizer management strategies. If one or more of the strips resulted in higher yields then it could be assumed that either the nutrient was under-applied by the producer, or in the case of N, lost.  That study concluded that at 75% of the locations, yield was maximized by the producer with [their respective] NPKS management system, however the greatest responses came from the addition of P and that Oklahoma State University’s soil testing and analysis was adequate for nutrient recommendations. That studies results were published in 2017 and is open access, so available for anyone to read. https://dl.sciencesocieties.org/publications/cftm/abstracts/3/1/cftm2017.02.0014

Locations of double crop fertility response strips applied in the summers of 2016 and 2017.

There are many producers around the state that follow winter wheat with double crops (DC). Often, this practice is done with limited inputs to reduce economic risk.  Oklahoma State does not make different recommendations for DC or full season crops, with the exception that yield potentials can differ.  In 2016 and 2017 we duplicated the Wheat NPKS study across 3 double crops (soybean, grain sorghum, sunflower) following winter wheat and canola. With a recent climb in DC yields we wanted to investigate if producers were applying enough nutrients to maximize grain yield. Additionally it would allow us evaluate the accuracy of OSU’s soil test based fertilizer recommendations in a double crop. Over the two years, 61 on-farm sites ranging from central to NE Oklahoma had 200 lb/ac of product per nutrient applied in strips 6ft wide by 150 ft long.  Urea (46-0-0), triple super phosphate (0-46-0), muriate of potash (0-0-60), and gypsum (0-0-0-19) were used for sources N, P, K, and S, respectively (92 lbs N, 92 lbs P, 120 lbs K, 38 lbs S). In most cases the fertilizer was applied post planting and post-emergence to ensure strips were applied an areas with good stand.

NPKS Strip Applicator. This ground driven 3pt rig uses Gandy boxes to deliver fertilizer into tubes which is then blown, by a PTO driven fan, out into strips 6 feet wide, per box. This applicator was putting out 200 lbs of Urea, 0-46-0, potash, and gypsum out per acre.

Much like with the wheat-NPKS study 75% of the locations did not respond to additional fertilizer. Twenty treatment comparisons of the 244 made across all 61 locations (50 soybean, 7 grain sorghum, 4 sunflower) yielded a statistically significant change in yield due to the addition of N-P-K-or S. For this report, a comparison was the yield of each nutrient versus the non-treated check, therefore there were four comparisons made per location. Seventeen of the twenty positive responses were found in soybean, three with grain sorghum, and no responses were found in sunflower plots.  Lack of response from grain sorghum and sunflower locations is contributed to small amount of grain sorghum and sunflower fields in the study.

Double crop soybeans in Ottawa County with strips of nitrogen, phosphorus, potassium, and sulfur applied post plant.

Nitrogen rates, for non-legumous crops, are yield driven, meaning the higher yielding a crop, the higher amount of N required.  Both grain sorghum and sunflower crops, due to neither being legumes, were expected to see N response, especially to those locations that applied little to no N to begin with.  A yield response from the addition of N was found in one grain sorghum location, where the producer application was not enough to maximize yield, and the additional N pushed the yields.  As expected, there were no soybean locations that responded to the addition of N.

Phosphorus and potassium are both sufficiency based, not yield driven.  This means that if the soil is at 100% sufficiency, the crop will produce at its highest rate achievable, based on that nutrient.  100% sufficiency for P and K are approximately 65 STP and 250 STK, respectively.  Phosphorus and potassium strips yielded the most results, especially in soybean locations. Of 20 responses, five responses were due to P, ten due to K, and four due to S. Locations that responded to the addition to P were locations that either had low levels of STP (approx. 80% sufficiency or less), or had low pH, which leads to less availability of P (pH>5.0).

Potassium yielded the most positive results, with ten responsive locations, as well as the most interesting results, with only three sites falling below 100% sufficiency.  The other responses were attributed to having low Cl levels (Cl, as in Chloride, which while responses are rare, is a necessary nutrient, and sometimes can lead to losses in yield, especially in sandy environments), as well as drought stress conditions.  Potassium has been shown to have a vital role in nutrient uptake and water retention, as it is found to be critical for root growth, and these are displayed highest in crops found in drought like conditions. One hypothesis for the K response is related to root growth. The later planted DC will spend less resources in root development before going reproductive. Soybean is a heavy user of K, combine smaller roots, typically hot drier soils, and high K demand it is not surprising to find this occurrence.

Sulfur, while not wide-spread reported in Oklahoma, has recommendations by OSU built on a yield driven scale.  There were four responsive locations found in this project. While one location had low soil test S values there were located areas that received high rainfall events during the growing season, and therefore the response was attributed to leaching of S.

So, after all that, what is the bottom line?  Here is our observations:

  • Producers maximized yield 75% of the time, with 25% of locations responding to any additional nutrient.
  • The 20 responses to additional nutrients occurred across 15 locations, four locations had responses to more than one nutrient
  • By nutrient: Note for P and K, due to site variability it was not expected to observe statistic yield increase due to P or K unless soil test was below 70% sufficiency, of which no location had soil test P or K below 70%.
    • 38 locations were below 100% sufficiency of phosphorus, with five observed responses
    • Seven locations were below 100% sufficiency of potassium, two observed responses. An additional eight locations responded that were not predicted by soil test
    • Based on pre-plant soil test there were no sites expected to respond to the addition of Sulfur, 4 locations did respond.
  • Soil test results were adequate in correctly identifying locations that would not respond to the addition of nutrients (93.5% accurate), while not as accurate at predicting sites that would respond.
  • For K, soil testing was less accurate, as eight of the ten responsive locations had soil test values above 250 soil test K (125 ppm or 100% sufficiency). For this reason, we are currently doing work evaluating K recommendations for soybeans.

This work confirms that of the fields we evaluated, the majority was not yield limited by N, P, K or S. However, as with anything, we have more work to do in order to further refine our recommendations, and always looking to learn more about how to aid producers.

Now may not be the time for Replacement

For phosphorus (P) and potassium (K) fertilizer management there are three primary schools of thought when it comes to rate recommendations. The three approaches are Build-up, Maintenance/Replacement, and Sufficiency. There is a time and place for each one of the methods however the current markets are making the decision for the 2016-16 winter wheat crop a very easy one. The OSU factsheet PSS-2266 goes in-depth on each of these methods. For the rest of the blog I will use P in the conversation but in many scenarios K should/could be treated the same.

Build-up is when soil test is below a significant amount of fertilizer, about 7.5 lbs P2O5 per 1 ppm increase, is added so that soil test values increase.  This method is only suggested when grain price is high and fertilizer is relatively cheap.  Given the market, this is a no go.  The two most commonly used methods of recommendation are Replacement and Sufficiency. In the replacement approach if the soil is at or below optimum P2O5 rate it based upon replacing what the crop will remove. The sufficiency approach uses response curves to determine the rate of P that will maximize yield. These two values are typically quite different.  A good way you boil the two down is that replacement feeds the soil and sufficiency feeds the plant.

Oklahoma State Universities Soil, Water, and Forage Analytical Lab (SWFAL) provides recommendations utilizing sufficiency only while many private labs and consultants use replacement or a blended approach.  Some of this is due to region.  Throughout the corn belt many lease agreement contain clauses that the soil test values should not decrease otherwise the renter pays for replacement after the lease is over. For the corn belt both corn and soybean can be expected to remove 80 to 100 pounds of P per year.  Conversely the Oklahoma state average wheat crop removes 17 lbs P a year.  In areas where wheat yields are below 40 bushel per acre (bpa) using the sufficiency approach for P recs can increase soil test P over time.

This conceptual soil test response curve is divided into categories that correspond with below opti-mum, optimum and above optimum soil test values. The critical level is the soil test level, below which a crop response to a nutrient application may be expected, and above which no crop response is expected. At very high soil test levels crop yield may decrease. *Rutgers Cooperative Extension Service FS719

This conceptual soil test response curve is divided into categories that correspond with below opti-mum, optimum and above optimum soil test values. The critical level is the soil test level, below which a crop response to a nutrient application may be expected, and above which no crop response is expected. At very high soil test levels crop yield may decrease.
*Rutgers Cooperative Extension Service FS719

Back to subject of this blog, consultants, agronomist, and producers need to take a good look at the way P recs are being made this year.  Profitability and staying in the black is the number 1, 2, and 3 topic being discussed right now.  The simple fact is there is no economic benefit to apply rate above crop need, regardless of yield level. The figures above demonstrate both the yield response to fertilizer based upon soil test. At the point of Critical level crop response / increase in yield is zero. What should also be understood is that in the replacement approach P fertilizer is still added even when soil test is in Optimum level.  This also referred to as maintenance, or maintaining the current level of fertility by replacing removal. If your program is a replacement program this is not a recommendation to drop it completely. Over a period of time of high removal soil test P levels can and will be drawn down. But one year or even two years of fertilizing 100 bpa wheat based on sufficiency will not drop soil test levels. On average soils contain between 400 and 6000 pounds of total phosphorus which in the soil in three over arching forms plant available, labile, and fixed. Plant available is well plant available and fixed is non plant available.  The labile form is intermediate form of P.  When P is labile it can be easily converted to plant available or fixed. When a plant takes up P the system will convert labile P into available P. When we apply P fertilizer the greatest majority of was is applied makes it to the labile and fixed forms in a relatively short period of time.  For more in-depth information on P in the soil you can visit the SOIL 4234 Soil Fertility course and watch recorded lectures Fall 2015 10 26-30 Link .

How to tell if your P recs have a replacement factor, not including calling your agronomist. First replacement recs are based on yield goal, so if you change your yield goal your rate will change.  The other and easier way is to compare your rates to the table below.  Most of the regional Land Grant Universities have very similar sufficiency recs for wheat.  Another aspect of the sufficiency approach is the percent sufficiency value itself.  The sufficiency can provide one more layer in the decision making process for those who are near the critical or 100% level.  Response and likelihood of response to P is not equal. At the lowest levels the likelihood of response is very high and the yield increase per unit of fertilizer is the greatest. As soil test values near critical (32.5 ppm or 65 STP) the likelihood of response and amount of yield increase due to fertilizer P decreases significantly.  At a STP of 10 the crop will only produce 70% of its environmental potential if P is not added while at a STP of 40 the crop will make 90% of its potential.  The combination of % sufficiency and yield goal can be used to determine economic value of added P.

*Oklahoma State University Soil Test Interpretations. PSS-2225 *Mehlich 3 and Bray P are similar *PPM (parts per million) is used by most labs *STP (soil test P) is a conversion used by some Universities. Equivalent to pounds per acre. * for a 0-6” in soil sample PPM * 2 = STP.

*From Oklahoma State University Soil Test Interpretations. Fact Sheet PSS-2225
*Based on Mehlich 3
*PPM (parts per million) is used by most labs
*STP (soil test P) is a conversion used by some Universities. Equivalent to pounds per acre.
* for a 0-6” in soil sample PPM * 2 = STP.

This data is available from OSU in multiple forms from the Factsheet PSS-2225, the SWFAL website, Pete Sheets quick cards, and the Field Guide App.

soapbox_ST

This year with margins tight soil testing is more important than ever before.  Knowing the likelihood of response and appropriate amount of fertilizer to apply will be critical maximizing the return on fertilizer invest while maximizing the quality and amount of grain we can produce.  Visit with your consultant or agronomist to discuss what the best approach is for your operation. Lets ride this market out, get the most out of every input and come out of this down cycle strong.

Feel free to contact me with any questions you may have.
Brian
b.arnall@okstate.edu

 

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.

Results from 1st year of Soybean Starter Work

In the spring of 2014 we initiated what was to be the first year of a three year project evaluating starter fertilizers for soybean production in the southern Great Plains.  The first and second year was and is being funded by the Oklahoma Soybean Board.

Year one was a bit experimental in that with so many products on the market we needed some initial work to help focus the direction for years two and three.  I also added a treatment which I knew would have significant negative impact, for extension reasons.  Keep in mind two locations in a single year does not make an experiment nor provide enough information to draw a definite conclusion.   It is however enough to learn some lessons from and for us to plan for our 2015 trials.

The 2014 trial consisted of 12 treatments, Figure 1 and Figure 2.  In these treatments I wanted to see the impact of a standard practice, see if a specific nutrient may be more so beneficial, and evaluate a few popular products.  The spring of 2014 started out dry so at one of our two locations we pre-watered.  This was done by hauling water to the Lake Carl Blackwell (LCB) 1000 gallons at a time and pumping through sprinklers.  The other site, Perkins, we delayed planting until we had moisture.

Treatment Structure and rates for the 1st year of the Soybean Starter Study.

Treatment Structure and rates for the 1st year of the Soybean Starter Study.

List of fertilizers and products used.

List of fertilizers and products used.

Image taken while planting the Soybean Starter study at Perkins.  A CO2 system was used to deliver starter fertilizers with seed.

Image taken while planting the Soybean Starter study at Perkins. A CO2 system was used to deliver starter fertilizers with seed.

The two locations were also selected due to differences in soil fertility.  The LCB site is has good soil fertility, with exception of phosphorus (P), and the Perkins site pH was an issue.  I would have expected a benefit from adding P at both of these locations.  Figure 4 shows the soil test results.

Soil Test results from LCB and Perkins.

Soil Test results from LCB and Perkins.

At LCB as expected some of the treatments (Thio-Sul) reduced stand, some unexpectedly reduced stand (Fe) and others had less impact on stand (APP 5.0) than expected.  The growth at LCB was tremendous, the 30 in rows covered over very quickly and the majority of the treatments hit me waist high by early August (I am 6’0”).  Many of the treatments showed greater growth than check.  But when it comes down to it, grain pays and green does not.  Statistically there were no treatments that out preformed the un-treated check, however the K-Leaf and 9-18-9 did make 3 and 2 bpa more than the check respectively.  What I am hypothesizing at this site is that the added nutrients, especially those with high P levels, significantly increased vegetative grown and these big plants were delayed into going reproductive and they started setting pods later in much hotter weather.  While riding in the combine I could see that the plots with compact plants with clearly defined rows out yielded those were the vines had crossed over and we harvested through more of a solid mat of mature plants.  A hot August is not uncommon and I am curious on whether this trend repeats itself.  If it does this may direct us into research evaluating ways to force/promote the reproductive stage to start in these big plants.  Even if we can force flowering to start earlier, it’s unknown whether yields will increase or not.

Yield and Stand counts from the 2014 LCB Soybean Starter Study.

Yield and Stand counts from the 2014 LCB Soybean Starter Study.

The Check plot at LCB were plants noticeably a bit smaller and more yellow than the neighbors with phosphorus.

The Check plot at LCB were plants noticeably a bit smaller and more yellow than the neighbors with phosphorus.

Soybeans at LCB on August 4th.

Soybeans at LCB on August 4th.

The same trends in treatments reducing stand can be seen at Perkins, however the impact was less extreme.  Perkins being planted later due to waiting on moisture forced a later flowering date and I believe reduced overall yields.  But the addition of P at this low pH site definitely made a difference.  While again no treatments were statistically greater than the un-treated check the 2.5 gpa APP, DAP broadcast, APP/H2O, and Pro-Germ/H20 treatments increased yield by 5.6, 4.2, 3.8 and 1.7 bpa respectively.

Yield and Stand Counts from the Perkins 2014 Soybean Starter Study.

Yield and Stand Counts from the Perkins 2014 Soybean Starter Study.

Take home from year one was that at LCB the addition of a starter fertilizer had little benefit and if done wrong could cost you yield while at the low pH site of Perkins an addition 2.5 gallons of APP did get a 5 bpa bump, but do to variability in the trial the increase was not statistically significant.  This year we will drop some of the treatments and incorporate a few new treatments.   Based on the current weather we look to potentially being able to start with better soil moisture at planting.  Again do not take this work and significantly adjust any plans you have for your 2015 soybean crop. This is however some interesting findings that I wanted to share and make everyone aware of.  Finally thank you to the Oklahoma Soybean Board for providing funding for this work. www.oksoy.org/ 

 

 

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.

 

snake-oil snake_oil_ad 60-60168_MECH

 

 

 

 

 

 

 

 

 

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

 

2013 Wheat and Canola preplant soil test results

Every few years I request the results of all soil samples submitted to OSU Soil, Water, & Forage Analytical Labs (www.soiltesting.okstate.edu) under the crop codes of winter wheat and winter canola.   Within this data set I can look at trends occurring across the state over time.  In this report I will focus on the 2013 results but make some comparison with the 2011 sample values.

As it pertains to mobile nutrients such as N, S, and B there is little that can be applied from the previous year’s soil samples because their levels in the soil change rapidly.  Samples must be collected every year to determine the current status.  However the soil test levels of immobile nutrients, P, K, Mg, ect are relatively stable over time and the recommendation is to take a close look at these values every three to five years.

In 2013 the number of sample submitted increase.  There were nearly 1000 more wheat soil samples (2733 to 3574) and 200 more canola soil samples (33 to 231).  If the distribution of nutrient levels of the two years are compared the only significant change is that the soil test NO3 level was significantly lower in 2013 (Tables 1 and 2).  This is attributed to the extremely dry 2012 spring and summer which delayed the breakdown of wheat straw and immobilization of residual N.

 

Table 1 and 2. Summary from all samples submitted to SWFAL under the wheat and canola crop codes in 2001 and 2013.

Table 1 and 2. Summary from all samples submitted to SWFAL under the wheat and canola crop codes in 2001 and 2013.

 

Reviewing the 2013 values the most concerning aspect is that 72% of the 3800+ soils samples had a Mehlich 3 P value below optimum soil test phosphorus (STP) of 65 (Figures 1 and 2). That adds up to 109,000 acres needing phosphorus, if you assume each sample represents 40 acres.    There is no way to determine how much P2O5 if any was applied to these particular fields.  However, an estimated impact of not fertilizing can be calculated.   Based on the Oklahoma typical average yield of just below 40 bpa, it would cost the state approximately 575,000 bushels if the land went unfertilized.  At $5.00 a bushel that is $2.8 million in revenue.  To remedy the low STP it would take approximately 2.76 million lbs P2O5 at a cost of $1.5 million ($0.50 per lb).

In the NPKS response study wheat fields across the state were evaluated for a response to additional (in addition to producer’s standard practice) nitrogen, phosphorus, potassium, and sulfur.    Phosphorus was the most limiting nutrient at 7 of the 59 harvest locations.  A response to P occurred more often than any of the other nutrients tested.   It is important to note at all seven fields had been fertilized with P that season, however each time it was below the OSU recommended rate.   The response study was a great reminder that it is important to have a good soil test and to follow the recommendations.

 

 

Figures 1 and 2. 1)Range of soil test P levels (Mehlich 3) for all samples submitted to SWFAL in 2013 under the wheat and canola crop codes. 2) Range of Soil Test P level for all samples with STP<65.

Figures 1 and 2. 1)Range of soil test P levels (Mehlich 3) for all samples submitted to SWFAL in 2013 under the wheat and canola crop codes. 2) Range of Soil Test P level for all samples with STP<65.

 

Soil pH on the other hand showed a slight improvement from 2011. The percent of samples under 5.5 decreased by 4%, 25 to 21. Of the samples <5.5 the majority fall within the 5.0-5.5 category, which for winter wheat is still within the optimum growth window (Figures 3 and 4).  These numbers are a good sign however two points should be made.  There is a significant amount of winter wheat acres that is not sampled; much of this is likely to fall below 5.5 soil pH.

 

Figures 3 and 4. 1)Range of soil pH levels  for all samples submitted to SWFAL in 2013 under the wheat and canola crop codes. 2) Range of soil pH levels for all samples with pH<5.5.

Figures 3 and 4. 1)Range of soil pH levels for all samples submitted to SWFAL in 2013 under the wheat and canola crop codes. 2) Range of soil pH levels for all samples with pH<5.5.

 

Additionally grid soil sampling and variable rate lime should consider on any field which the composite soil sample pH ranges from the high 4’s to the high 5’s.  For example a 75 ac field near Deer Creek had a composite soil sample test pH of 5.3 and buffer index of 6.5.  The OSU lime recommendation, for a wheat crop, was 2.2 ton per acre for a total of 166 tons to lime the entire field.  However the producer grid soil sampled the field himself at a 2.5 acre resolution (31 samples).  Figure 5, shows that the pH of the field ranged from 4.4 to 7.9.  Only 33 tons of lime would be required if the field were limed using a variable rate technologies.   Cutting the total amount applied by 133 tons would save the producer approximately $4000.

 

Figure 5. Soil pH results from a 75 acre field that was grid soil sampled at a 2.5 ac resolution.

Figure 5. Soil pH results from a 75 acre field that was grid soil sampled at a 2.5 ac resolution.

 

Oklahoma wheat and canola producers must take advantage of the weather when it goes their way.  Yet if the crop does not have the proper soil pH and nutrients under it, it will never reach its potential.  Take the time to collect a soil sample and send it in to a lab. The hour it takes to collect the sample a few dollars you spend on analysis will help ensure that crop you are producing has the best chance of hitting maximum yield in the most economically and environmentally sound manner.

 

Related Factsheets

OSU Soil Test Interpretations

http://npk.okstate.edu/documentation/factsheets/PSS-2225web2013.pdf

Fertilization Based on Sufficiency, Build-up and Maintenance Concepts

http://npk.okstate.edu/documentation/factsheets/PSS-2266web.pdf