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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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Rain makes grain, but also washes Nitrogen away.

Precipitation in the southern Great Plains is never something you take for granted. As I write this blog I am just wondering when it will be dry enough for long enough to finishing sowing my wheat, but I also remember just how dry it was last winter. The last three months, Aug-Oct rank as one of wettest in the states recorded history. Below are the 30, 60, and 90 day rain fall totals (as of 10.26.18) from Mesonet. By the 60 day map most the wheat belt is showing double digits and the 90 day maps shows a lot of our graze out wheat regions in the 20+ inch realm.

30 Day rainfall totals retrieved from Mesonet on 10.26.18.  Putting recording window from Sept 26-Oct 26. http://www.mesonet.org/index.php/weather/category/rainfall

60 Day rainfall totals retrieved from Mesonet on 10.26.18.  Putting recording window from Aug 27 – Oct 2 http://www.mesonet.org/index.php/weather/category/rainfall

90 Day rainfall totals retrieved from Mesonet on 10.26.18. Putting recording window from July 28-Oct 26 http://www.mesonet.org/index.php/weather/category/rainfall

I bring up graze-out wheat for a reason, to get as much forage as possible it is planted as early as possible. I know of fields that were seeded in July and early August. And to produce this great quality forage, nitrogen fertilizer is applied pre-plant. It just so happens that this July more fertilizer was sold than any other month since I have been in Extension. In July producers bought nearly 1/3 of totoal tons of fertilizer what is typically sold in a single year. While a portion of this may have been pre-purchased for later delivery, I know a lot of it made it to the field. To see why this matters, lets take a look at the nitrogen cycle.


The nitrogen cycle is made up of a central component (Organic Matter), three N sinks (Microbial/Plant, Atmosphere, Nitrate {NO3}), four loss pathway (Ammonia Volatilization, Leaching, Plant Loss, Denitrification), and five additions (N2 Fixation, Fertilization, Lightning/Rainfall, Industrial Fixation, Plant/Animal Residues). We are going to spend the next bit talking about what is happening in the bottom right corner and left hand side.

When we put anhydrous ammonia (NH3) in the soil it pulls a hydrogen (H) from water and turns in to ammonium (NH4). Urea goes through a similar process but has to first be converted to NH3 by the enzyme urease.  Ammonium is important because it is a positively charged ion (cation) which will be fixed on the cation exchange sites. This means is it not going to move around in soil, but is readily available for plant uptake. However when NH4 is in a soil with temperatures above 50 degrees and in the presence of oxygen the two bacteria nitrosomonas and nitrobacter convert it to NO3. Given warm soils and our good soil moisture levels it very likely that any N applied in July or August would have converted 50% or more of its NH4 into the NO3 form by this point.

Nitrification portion of the Nitrogen Cycle. Complete Nitrogen Cycle. http://psssoil4234.okstate.edu/lecture

Nitrate is a negatively charged ion (anion) which is repelled from the negatively charged soil. This is beneficial for plants as when they take up water, NO3 is taken up though mass flow. The downside is that since NO3 is in the soil solution, where ever the solution goes so does the NO3, that is called leaching. So in well drained soils the recent rains will have caused a fair amount of leaching.  For some areas the NO3 that is leached below the root zone and could potentially be drawn back up as the soils dry. But there are going to more scenarios in which the N is gone, or at least gone elsewhere. In a sloping field the soil water will hit a limiting layer or clay increase layer and move down slope. I have already seen many wheat fields that are showing yellowing on side slopes.

Unfortunately leaching isn’t the only way we are losing N during this wet cycle. Denitrification occurs when the soil is saturated and oxygen (O) levels are depleted.  In anaerobic conditions, microbes strip O from NO3 reducing it gaseous forms. Typically it takes about one week of standing water to start seeing high levels of denitrification.

Nitrate loss pathways of the Nitrogen Cycle.
Complete Nitrogen Cycle. http://psssoil4234.okstate.edu/lecture

What does this all mean? Conservative guess is that for July or early August applied N we could be looking at losses of 50% or more.  This is a rough guesstimate of course, a fields soil texture, slope, soil type, tillage etc will all impact the loss amount.  As the date of application moves closer to Oct there will have been less nitrification and less total rainfall. What I can say with 100% certainty is that if N fertilizer was applied any time from July through early September, N has been lost.

So whats my N manage recommendations? First, foremost, and always This is the perfect scenario where N-Rich Strips will pay off! (Here’s a blog on N-Rich Strips https://osunpk.com/2013/09/19/nitrogen-rich-strips/). The N-rich Strip will allow you to detect N stress early, which for grazers is important. Close attention needs to be paid on fields with wheat being grown for grazing, N deficiencies will reduce forage production and gain. If the N-Rich strip shows up or there are signs of N deficiencies (yellowing of older leaves from the tip toward the collar) its time to be looking at applying N. For grain only fields we have some time. It is important though that as we get closer to spring and hollow stem we are taking care of the crops N needs. Here is a link to a blog on reading the N-Rich Strips to get a N rate rec https://osunpk.com/2014/02/24/sensing-the-n-rich-strip-and-using-the-sbnrc/ and here is a link to one of my latest blogs on Timing of Nitrogen Application for Wheat https://osunpk.com/2018/10/01/how-long-can-wheat-wait-for-nitrogen/.

For more information please contact me at b.arnall@okstate.edu


Below is a Sunup TV video on the subject of Nitrogen Losses with the recent rains.




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.


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.


2015-16 Wheat Crop Nitrogen Review

From trials to phone calls (and text messages, and tweets, and ect. ect) I have gathered a fairly good picture of this years winter wheat nitrogen story.  And as normal, nothing was normal.  Overall I seen/heard three distinct trends 1) Did not take much to make a lot 2) took a ton to make a lot 3) saw a response (N-rich strip or cow-pow) but fertilizer never kicked in. Covers most of the options, doesn’t it.


The N-rich strips really came out over all very good this year.  N-Rich Strip Blog. On average many of those using the N-Rich Strip and SBNRC (SBNRC Blog) producers have been getting in the neighborhood of 1.0-1.3 lbs of N applied per bushel produced.  This year the numbers ran from 0.66 to 2.3 lbs of N per bushel.  In both extremes I believe it can be explained via the field history and the N-Cycle.


Nitrogen Cycle Pete’s Sheet

In at least two fields, documented with calibrated yield monitors, the N-Rich Strip and SBNRC lead to massive yields on limited N. One quarter of IBA bumped 86 bpa average on 47 lbs of N while a second quarter, also IBA, managed 94 bpa average on about 52 units of N. We are currently running grain samples from these fields to look protein levels.

The other side of the boat were those with N-Rich strip calling for +2.0 lbs N per bushel.  I had received notes from producers without N-rich strips saying that they could predict yield based on the amount of N applied and it was a 2 to 1 ratio.  Not always but many of these high N demand fields where wheat following a summer or double crop or corn or sorghum. While many of the low N demand fields were wheat after wheat or wheat after canola. In a rotational study that had been first implemented in the 2014-15 crop year I saw big differences due to previous crop.  The picture below was taken in early March.  The straw residue in wheat after wheat had just sucked up the nitrogen.  While it was evident the residue from the canola broke down at a much more rapid pace releasing any and all residual nutrients early.


The yield differences were striking. The canola rotation benefited the un-fertilized plots by 22 bpa and even with 90 lbs of N applied having canola in the rotation increased yields by 12 bpa.  We are looking and grain quality and residual soil sample now. I am sure there will be a more indepth blog to follow.

Canola Wheat Rotation study year two yield average. yields average across previous years N-rates.

Canola Wheat Rotation study year two yield average. yields average across previous years N-rates.

Another BIG story from the 2015-16 wheat crop was the lack of benefit from any N applied pre-plant. It really took top-dress N this year to make a crop.  Due to our wet early fall and prolong cold winter N applied pre was either lost or tied up late.  Work by Dr. Ruans Soil Fertility Program really documented the lack luster pre-plant N effect. The figure below shows 4 location of a rate by timing student.  The number at the bottom of each graph is a rate by time (30/0 means 30 lbs Pre-0 lbs Top, 60/30 means 60 lbs Pre-30 lbs Top).  At every single location 0/60 beat 60/0. Top-dress N was better than Pre-plant N.


Figure 1. Work from Ethan Driver and Dr. Bill Raun. Study looked at rate and timing of N fertilization in wheat. Treatments are ordered by total N applied.

The last observation was lack of response from applied N even though the crop was deficient.  Seen this in both the NE and NW corners.  I would hazard with most of the circumstance it was due to a tie up of applied N by the previous crops residue.  The length at which the winter stretched into spring residue break down was also delayed.

Take Home 

Here it is folks APPLY NITROGEN RICH STRIPS.  Just do it, 18 years of research preformed in Oklahoma on winter wheat says it works. Hold off on heavy pre-plant N even if anhydrous is cheap.  It does matter how cheap it is if it doesn’t make it to the crop.  Will we see another year like 2015-16, do not know and not willing to place money on either side. What we do know is in Oklahoma split applying nitrogen allows you to take weather into account and the N-Rich strip pays dividends.

There are several fact sheets available on top-dressing N and the application of N-Rich strips.  Contact your local Oklahoma Cooperative Extension Service county educator to get a copy and see if they have a GreenSeeker sensor on hand.

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.


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.


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.

Herbicide and UAN tank mixed for top-dress

Spring is the time that many wheat producers apply herbicide and nitrogen (N) fertilizer.  For many this can be accomplished in a single pass by tank mixing the herbicide and UAN. In most cases this is an effective practice which eliminates one pass over the field.  There are some scenarios in which this practice is ill advised. One such scenario is high temperatures which would lead to excessive leaf burn and crop damage. The other scenario is no-till and that will be the focus of this article. Ruling out warm temperature tank mixing herbicides and nitrogen, assuming the herbicide can be tank mixed, is a good practice.  No-till on the other hand can be a different issue.

No till drill and ammonia oxide application

Situations with a lot of residue and smaller wheat is common during top-dress.

The problem in no-till comes from the liquid application method needed to apply herbicides, flat flan. To get a good kill with the herbicide the spray pattern needs to have good coverage, i.e a lot of small droplets to ensure maximum surface area impacted.  Unfortunately there are four primary fates of UAN  when applied via flat fan nozzles.  The UAN could be taken directly up into the wheat plant via absorption through the leaves, the UAN could reach the soil and go into the soil solution or absorbed onto the soil itself, the UAN can be taken up by weeds, or the UAN droplet may hit dead plant tissue and be adsorbed into the residue.


UAN applied with a flat fan will hit a growing plant, the soil, or residue.

The fourth fate of UAN presented is what can make the tank mix less efficient than a two pass system.  In a no-till system any UAN that hits residue should be counted as lost, for the short term. The decision to go with a one pass or two pass system can be aided by evaluating the amount of canopy coverage.  For example if the no-till field has 50% canopy coverage then one could estimate 50% of the UAN applied via a one pass system would be tied up in the residue.  The cost of a second application could then be compared to the lost N.  If 15 gallon of 28-0-0 was being applied then approximately 22.5 lbs of N would be tied up by the straw. At a price of $0.40 per lb on N, that is $9.00 worth of N.  Conversely if the canopy coverage was 80% only 20% or 9 lbs of N would be tied up in the residue. Saving the $3.60 in nitrogen would not justify a second trip over the field. Luckily OSU recently released the Canopeo app which uses a cell phones camera to take pictures and quickly and accurately determine % canopy coverage.  Canopeo is available for iOS and android http://canopeoapp.com/.

In fields with a high amount of residue or limited canopy coverage UAN should be applied with streamer nozzles.  This will concentration the fertilizer into streams which will allow the UAN to have enough volume to move off the residue and into the soil.

So as the decision is being made to tank mix herbicide and UAN or make two passes take into consideration: % canopy coverage, rate of UAN (how much could be lost), cost of UAN per pound, and cost of a second trip over the field.

Below is an excerpt from the publication Best Management Practices for Nitrogen Fertilizer in Missouri; Peter C. Scharf and John A. Lory. http://plantsci.missouri.edu/nutrientmanagement/nitrogen/practices.htm

Broadcasting UAN solution (28 percent to 32 percent N) is not recommended when residue levels are high because of the potential for the N in the droplets to become tied up on the residue. Dribbling the solution in a surface band will reduce tie-up on residue, and knife or coulter injection will eliminate it. Limited research suggests that the same conclusions probably apply for grass hay or pasture. Broadcast UAN solution is also susceptible to volatile loss of N to the air in the same way as urea, but only half as much will be lost (half of the N in UAN solution is in the urea form).

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)


Canola Planting Considerations.

Pre- and Early-Season Weed Management-

Dr. Angela Post- Small Grains Extension Weed Scientist

Winter canola is an excellent rotational partner with wheat.  Integrating canola into a wheat system allows for the cleanup of weedy fields with primarily grassy weed problems. Conventional and Roundup Ready (RR) varieties are excellent choices for managing most grassy weeds including ALS-resistant populations, because grass-only herbicide options can be used in canola without crop injury.  For specific grasses that are very difficult to control, like cereal rye and jointed goatgrass, it is advisable to use canola in year one of your rotation and Clearfield wheat in the second year of your rotation before going back to conventional wheat varieties. Due to sensitivity of canola, Clearfield wheat varieties should not be used the year prior to rotating into canola.

Canola planting time is just around the corner and many are going out now with preplant burndown applications.  Remember that canola is sensitive to dicamba, 2,4-D, and MCPA and these products should not be used inside of 30 days before planting.  Glyphosate, glufosinate and paraquat are all potential options for removing broadleaf weeds in no-till systems prior to planting.  These products have no planting restriction for canola. Tillage is the best option to remove weeds in conventionally tilled systems.

It is important to consider your previous herbicide choices when planning for canola in the fall.  Many herbicides used for spring weed control in wheat can limit rotation to winter canola.  These include all Group 2 herbicides all of which have long rotation restrictions to canola, meaning you cannot plant canola in these fields for 18-24 months depending on the product.  See Table 1 for a list of specific restrictions. If you have used one of these products in wheat in the spring, you must plant a canola variety with the SURT trait.  Examples of varieties with this trait include:  DKW 45-25, DKW 46-15, DKW 47-15, HyClass 115W, HyClass 125W.  All of these varieties are also RR.  Kansas State also has an open-pollinated non-RR variety called Sumner with the SURT trait for growers that prefer to grow conventional canola.  Note that the SURT trait is not a genetically modified trait.

No additional in-season herbicide options have been added to the toolbox for winter canola growers in the upcoming season.  Both trifluralin (Treflan) and ethalfluralin (Sonolan) can still be used as preemergent weed control options in canola in conventionally tilled systems.  Both need to be mechanically worked into the ground and need an activating rainfall to work properly.  Quizalofop (Assure II), sethoxydim (Poast), and clethodim (Select and many generics) are the grass control herbicides available for use in canola and can be used on any canola variety including RR varieties.  Roundup Ready canola growers are allowed two applications of glyphosate at 22 oz/A each over the top of the emerged crop.  Clopyralid (Stinger) is the only over-the-top broadleaf control option other than glyphosate. These weed control applications should be made early in the season between 2- and 6-leaf canola, and prior to bud formation, while weeds are still very small.  Applications should be spaced at least 14 days apart.  Early applications will eliminate fall weed competition with canola and protect yield. For more information or questions involving weed management in canola contact Extension Weed Specialist Angela Post at 405-744-9588 and follow @OSUWeedScience.

Table 1.  Rotation restrictions for planting canola following wheat.  For herbicides
applied in crops other than wheat please refer to the herbicide label.

1Minimum interval between herbicide application and seeding canola. Refer to full herbicide labels for specific information as geography, pH, and rainfall may affect this interval. 2Rotation restriction can be overcome with use of a SURT canola variety. 3Rotation intervals depend on geography. 4Rotation interval depends on herbicide rate.

1Minimum interval between herbicide application and seeding canola. Refer to full herbicide labels for specific information as geography, pH, and rainfall may affect this interval.
2Rotation restriction can be overcome with use of a SURT canola variety.
3Rotation intervals depend on geography.
4Rotation interval depends on herbicide rate.

Pre plant fertilizer concerns with Canola

Dr. Brian Arnall- Precision Nutrient Managment Extension Specialist

When it comes to pre-plant fertility issues with canola, I typically have two soap boxes. But at this point in the canola game we are behind in terms of getting soil samples collected or applying lime and getting a boost at emergence.  So assuming pH is good and you know what your soil nutrient level is we can move on to planting.  One thing that over the past seven or eight years keeps coming up is the importance of starter fertilizers and the rates and sources used.  Getting that little canola plant off to a good start is extremely important however with that little bitty seed a little goes a long way.

The figure below shows the impact of DAP (18-46-0) placed in row, on relative canola stands, when canola was planted in 15” rows.  At 5 lbs/A of N or 28 lbs/A of DAP, the canola stand is reduced to 75%.  While this seems like a great loss, the compensating nature of canola and the fairly high seeding rates used, this is a manageable level. The benefits of the additional nitrogen and phosphorus applied with the seed also help out-weigh the loss of stand.  The addition of the P near the germinating seed is vital.  The phosphorus aids in early root and shoot growth, helping the crop to get off to a good start.  In areas where soil pH is of concern the P near the young seedling will reduce aluminum toxicity and allow the plant to tolerate the low pH.  Keep in mind, while banding P will help in acidic soils, canola is still very sensitive and will not tolerate the same low pH conditions as our winter wheat’s.

Impact of DAP (18-46-0) placed in-row on canola stand in terms of lbs N ac-1.

Impact of DAP (18-46-0) placed in-row on canola stand in terms of lbs N ac-1.

One very important factor to keep in mind is the impact of the critical rate and row spacing.  The 5 lbs of N per acre critical level set for 15” row spacing is increased to 10 lbs on 7.5’s and cut to 2.5 lbs on 30’s. The change in rate is because we use lbs per acre.  So if you apply the same amount of material per acre on a 15” spacing and a 30” spacing there is actually twice as much material in the 30” row.  Table 1, shows the equivalent amount of N placed in row for popular row spacing’s.

Equivalent amount of N based on 15" row spacing.

Equivalent amount of N based on 15″ row spacing.

Oklahoma State has released a smart phone app, available for both apple and android devices, to aid in determining maximum in-furrow rates.  Canola Starter app provides guidelines based upon the nutrient concentrations of the fertilizers you plan to use. The final note on in-furrow fertilizer with Canola, avoid using urea. The likelihood of injury from the urea converting to ammonia greatly outweighs any potential benefits.  For further information, comments, or questions please contact Dr. Brian Arnall Extension Precision Nutrient Specialist 405-744-1722 or following me on Twitter @OSU_NPK.

Canola Starter available on iOS and Android. For more information see http://www.dasnr.okstate.edu/apps.

Canola Starter available on iOS and Android. For more information see http://www.dasnr.okstate.edu/apps.


Winter canola planting decisions:

Josh Lofton- Cropping Systems Specialist

Josh Bushong- Extension Associate


Stand establishment is one of the most critical practices in canola planting.  This is not only because these stands are highly influential to end of the season yields but because getting the crop up with adequate growth will be critical to give the plants the best over-winter survivability possible.  To accomplish this, growers need to make sure they make good field selection and follow good planting practices

Field Selection:

Soil nutrients are a critical aspect.  Soil samples should be collected on a regular basis to ensure optimum productivity.  Also, ensure recommendations for winter canola are followed, as nutrient recommendations for other crops may be invalid. For more information canola fertilizer management refer to the nutrient management section by Dr. Arnall.

Winter canola grows similar to winter wheat.  Fields that can adequately produce wheat have the potential to produce canola.  These include, well-drained soils with adequate soil nutrients.  However, canola can be more sensitive than wheat. One aspect that canola can be more sensitive to is soil pH.  While wheat can be grown in soils as low as 5.5 without significant yield loss, canola must be grown on soils with pHs above 5.8.  In fact, canola is best grown in soils with soil pHs ranging from 6.0 to 7.0.  Therefore, it is essential that if fields have lower pH, lime be applied with adequate time to neutralize the acidic soil pH before rotating into canola.

In addition to all the soil conditions, crop rotation should be considered prior to planting canola.  One of the major hindrances in growing canola in rotation with other crops is herbicide carry-over.  For detailed information regarding this aspect, refer to table 1 in the weed management section.  To account for this, detailed field records should be kept and consulted before rotating with canola.

Planting Date:

Planting time depends on many aspects.  Insured growers should plant within the constrained planting dates.  For Oklahoma, the earliest planting date is September 10th with the latest date being October 10th.  However, within these guidelines, seedbed and environmental conditions should be the driving factor to determine when to plant.  The goal of these planting dates is to have the crop germinate, emerge, and establish 6-8 true leaves prior to the first killing freeze.  As a general rule, the crop should be planted 4 to 6 weeks before this freeze.  To achieve good establishment of the crop, canola should be planted into firm seedbed with adequate soil moisture.  If canola is planted into dry soil (dusted in), the effective planting date will be delayed until adequate conditions for germination and emergence exist.  In no-till systems, it is important to remember that canola emergence and growth will be slightly delayed.  Therefore, if adequate conditions exist, no-till fields should be planted before similar conventionally tilled fields.


Uneven canola emergence. Canola on left emerged later and did not have enough time to put on adequate growth (Photo courtesy of Josh Bushong)

Uneven canola emergence. Canola on left emerged later and did not
have enough time to put on adequate growth (Photo courtesy of Josh

Planting depth, plant spacing, and seeding rate:

Since canola is a small seeded crop, shallow planting is required.  For best germination and emergence, seeds should be planted between 0.5 and 1 inch.  If adequate moisture is available deeper, planting depth can be increased. However, deeper planting has the potential to decrease germination, percent emergence, and early fall growth, so deeper planting should only be used when the planting condition advantage is present and only on certain soils.  Therefore, caution should be used in planting deeper than 1 inch.  Furthermore, even though moisture may be present deeper, seeds should not be planted deeper than 1.5 inches.

Oklahoma growers have options when deciding row spacing used for planting canola and depend on what equipment there is available and their production system.  Since canola is typically rotated within a winter wheat production system, box drills and air seeders are typically widely available.  Row-spacing for these can range from 6 to 15 inches.  Row spacing within this range has little impact on final yields.  As producers move from drills and air seeders to planters, row spacing typically increases from 15 up to 30 inches.  All of the row-widths have the potential to produce adequate canola.  Some, however, will be more beneficial than others.  Narrow row spacing has the potential to result in early canopy closure, reduce potential weed competition, and may help reduce shatter prior to harvest (especially when direct harvested).  Wider spacing, however, allows for some flexibility in specialized planter attachments used, especially row-cleaners, which can be greatly beneficial in no-till systems.

Seeding rates for canola in Oklahoma range from 1 to 5 lbs/A.  However, row spacing plays a critical role on seeding rates.  When canola is planted on less than 15 inch spacing, some flexibility exists for planting rates.  Higher seeding rates can produce more uniform stands, uniform maturity, and thinner stalks that can greatly help harvest efficiency.  Too high of stands can increase disease incidence, winterkill, and lodging.  When row spacing is increased beyond 15 inches, care should be taken not to over seed.  High seed populations can increase fall growth and potentially increase hypocotyl height, which in turn can lead to high winterkill.  Optimum populations for this wider row spacing typically range from 2 to 3 lbs/A.

For further information, comments, or questions please contact Josh Lofton Extension Cropping Systems Specialist at 405-744-3389 or follow me on Twitter @OSU_oilseeds.

While producers have faced many challenges over the last couple of seasons in Oklahoma agriculture, the outlook for winter canola looks very promising for the upcoming season.  Producers should focus on taking all of the right steps to ensure the 2015-2016 crop starts on the right foot and takes full advantage of the promising conditions this season.  Good luck to everyone one on their upcoming production season and if anyone from Oklahoma State extension can help or assist in any way, please feel free to contact.