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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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Utilizing N fixing biologicals.

In the past couple years significant efforts have been made to produce N fixing microorganisms that can be utilized in an agriculture system. The atmosphere is 78% N2 and prokaryotic microorganisms such as the bacteria species Azotobacter, Bacillus, Clostridium, and Klebsiella take that N2 gas and turn it into plant available NH4. These organisms have been around providing nitrogen for plants, for as long as there has been plants. In agriculture we have heavily utilized their relationship with legumes however have struggled bringing them into other realms of production. Naturally they tend to be found in areas that are very low levels of nitrogen. For example, prokaryotes were found in the un-fertilized check of the 130-year-old Magruder Plots but are not found any other treatment that receives fertilizer organic or commercial.

 Nitrogen-fixing nodules on soybean roots. Image credit: Bo Ren, Purdue University

Now there are several products marketed as containing N fixing microorganisms suited for use in today’s corn, sorghum, and wheat production. While I have an active research program evaluating the use of such materials in Oklahoma, this blog will not address what works or how well. This blog will touch upon my thoughts on how to utilize a technology such as this if you pull the trigger to implement.

So there is one key to getting a ROI on products that create plant available nitrogen, and it’s a really simple key.
Under Apply Nitrogen
If you apply enough or more N than the crops needs, then there is ZERO value in a product that creates more N. For example, applying one of these products in your 250-bushel yield goal corn after you’ve already laid down 300 lbs of N preplant. Unless you lose it all to leaching, your probability of seeing a ROI on your biological investment is pretty poor. I have a hard time understanding the thought process behind paying for a N fixing product and not lowering your fertilizer rate. I can see one of two reasons. 1) You believe you historically under apply N and are losing yield because of such 2) Are in an environment which has a high potential of late season N losses, and you are unable to make recovery applications.

So what to do if using a N Fixer? I do not have the confidence yet to say, “Apply X product, it will produce Y lbs of N, so cut your rate by Y lbs”. That uncertainty is one of the greatest challenges, not knowing will I get 10 lbs or 40 lbs? If I did, then I would just subtract that off my planned rate. Side note, as someone who has been doing on farm N rate studies for a decade plus, I would have to add that most were likely over applying by that much and could cut back anyways. For me the use of the N Fixers should force your hand into utilizing in-season N applications, regardless the crop. So that you can better predict or determine impact of the product.

This is where the use of a refence strip (N-Rich or Zero N) is the golden ticket. We need a way to quickly evaluate the amount of N the crop has access to. The N-Rich method works best when preplant N is drawn way back. I would add that reduced pre-plant is a great scenario for N Fixers. The N-Rich in comparison to the rest of the field will provide you guidance towards your in-season goals. If the N-Fixers are doing a great job the N-Rich will not be showing up any time soon and you can make your N rate adjustments accordingly. If you are a Pre-plant or die kind of farmer, then I say you need to pull back the reins on the preplant rate but give the N Fixers some room to add value and add in your Zero N strips. These will again let you observe what is happening in the soil apart from your fertilizer. If it is getting on the late side of in-season N and you cannot find your zero, might be a good time to walk away and hang up the fertilizer applicator keys. I have lots of blogs and pubs on the use of reference strip so send me a note if you want to dive further into these approaches.

Nitrogen Rich Strips being applied in winter wheat. Photo credit: Zack Rendel, Rendel Farms Miami Oklahoma.

Feel free to reach out with questions or comments. B.arnall@okstate.edu

Related Blogs

Pre-plant Irrigation

Sumit Sharma, Irrigation Management Extension Specialist.
Jason Warren, Soil and Water Conservation Extension Specialist.

Pre plant-irrigation is a common practice in Western Oklahoma to recharge soil profile before growing season starts. Pre-plant irrigation is useful when the irrigation capacity is not enough to meet peak ET demand.  It can also be important to germinate and provide for optimum emergence of the crop.  As such, pre-plant irrigation is not useful when the soil profile is already wet, or soil profile is not deep enough to store moisture, or if planting dates are flexible and can wait until rains can recharge soil profile. Pre-plant irrigation becomes an important consideration if the previous crop had extensive rooting systems, which depleted moisture from deep in the profile. The crops in western Oklahoma especially in the Oklahoma Panhandle depend on stored water in the profile to meet ET demand during peak growth period, especially when well capacities are limited. Deep profiles and excellent water holding capacities of soil found in the region make the storage of a considerable amount of moisture possible. While pre-plant irrigation to recharge the whole profile (which can be 6 feet deep) may not be possible or advised, producers can still use certain tools to assess the stored water in the profile and make decisions on pre-plant irrigation.

A soil push probe (Figure 1) can provide a crude estimate of the moisture in a soil profile. For example, if an average person can push the probe to 2 feet, this means that the first 2 feet of the profile has moisture stored in it. The profile beyond 2 feet is considered too dry to push the probe through. This method does not provide the amount of water stored in the profile. For accurate measurements of soil moisture, soil samples could be collected, weighed, dried and weighed again to determine the water content in the soil.  An alternative is to install moisture sensors, however this is usually not practical due to potential damage during planting, although some probes that can be permanently buried are becoming available. On average a clay loam soil in western Oklahoma can hold up to 2 inches of plant available water per foot. The approximate water holding capacity of your soil can be found on the websoilsurvey.  Your county extension or NRCS personnel should be able to help you navigate this website if necessary.  When the water holding capacity of your soil is known, the use of a push probe can provide a preliminary estimate of soil water content. Probing should be done at multiple locations in the field on both bare and covered (with crop residue) spots. The presence of crop residue reduces evaporation and increases infiltration so the first thing you will notice is that it is generally easier to push the probe into the surface where the ground is covered by residue. If the soil water content is near full the probe will be easy to push into the soil and it may even have mud on its tip when you pull it out. In this case you can estimate that the water content to the depth of penetration is near field capacity and that the current water content is equal to the water holding capacity.  For example, if you can push the probe 2 ft into a soil with a water holding capacity of 2 inches/ft then we expect to have 4 inches of plant available water.  In contrast if it takes some effort to push the rod 2 ft the estimated water content may be reduced. 

Figure 1: A probe pushed in the ground to check profile moisture.

When pre-irrigation is applied it can be useful to assess the increase in the depth to which the probe can be pushed into the soil after the irrigation event.  For example, if 1 inch of irrigation is applied to the soil in the example above, we may expect that after this irrigation event we can push the rode 2.5 ft.  However, in some case we may be able to push the rod 3 ft. The reason being that although we could not push the rod beyond 2 ft before the irrigation event, the soil below this depth was not completely dry.  Therefore, the 1 inch of water was able to move to a depth of 3 ft. This is useful information, telling us that the soil below the depth we can push the rod contains some water and that each inch we apply may drain a foot into the profile.   Generally, we expect the rooting depth of most crops to be able to extract water from at least 4 ft.  Although it is certainly possible to extract water from below this depth, we generally don’t want to pre water our soils to full beyond 4 ft. When we fill the profile with pre water, we are increasing success of the following crop by providing the stored moisture that can offset deficits that may occur in the growing season.  However, we are reducing our opportunity to capture and utilize spring rainfall.  We must consider this when applying pre-irrigation, because if it is followed by rainfall in excess of ET our irrigation efficiency is greatly reduced by the drainage or runoff that can occur.

The Easy Button for Nitrogen…….

Brian Arnall, Precision Nutrient Management Extension Specialist.

The basics for nitrogen (N) fertilizer rate determination can be described in a mechanistic approach by the Stanford Equation NFert = ( NCrop – NSoil ) / Neff. This equations states that the N fertilizer rate is equal to the amount of nitrogen taken up by the crop minus the amount of nitrogen supply by the soil, divided by the efficiency of the nitrogen fertilizer used. I outline the importance of this equation in the blog “Components of a variable rate nitrogen recommendations“.

There are nitrogen “Easy Buttons” which utilizes averages collected over diverse environments to create accurate N rate recommendations. The best example of this is the yield goal rules of thumb such as wheats 2.0 lbs N per yield goal bushel minus soil test nitrate. Yield goals are generally calculated as the average of the best 3 out of 5 years, or the 5-year average times 20%. Also, the 2.0 lbs of N is more than what is in a bushel as it also adds in an efficiency factor or a 0.5 lbs per bushel cushion. This method and others like it provide an accurate N rate with slight probability of yield loss. However, the rec is often highly imprecise. Meaning that if I apply the method to 100 fields the average will be spot on, however if I look at the performance of the recommendation on a single field, I will likely be disappointed.

Illustration of accuracy versus precision.
Figure 1. Illustration of accuracy versus precision.

When it comes to nitrogen recommendations the Easy button method will use components which help ensure that the rate prescribed will maximize yield 90-95% of the time. For example, take the data presented in Figure 2. Over fifteen years of the long-term winter wheat fertility study near Lahoma, Oklahoma the average pounds of N per bushel to reach economic optimum nitrogen rate (EONR) was 1.6, however if 2.0 of N was applied per bushel yield would have been maximized 13 out of the 15 years. While 2.0 lbs. of N per bushel would have been quite accurate for maximizing yield, it would be highly imprecise as over the 15 years optimum pounds of N per bushel ranged from 0.0 to 3.2.

Figure 2. Grain yield (bushels per acre), economical optimal N rate (EONR), and pounds of nitrogen per bushel producer at the EONR, from 15 years of data from the long-term fertility trials located near Lahoma, Ok.

The trick to improving your N rate recommendation closer to a precise and accurate system is to obtain representative site-specific values for the Stanford Equation NFert = (NCrop – NSoil) / Neff.

Looking at the 15-year long-term data above the yields range from a low of 27 to a high of 88 bushels. Of those 15 years, I personally planted multiple years, usually sometime in October, and many of those years while sowing I could have guessed a range of 55-60 bushel, which just happened to be just above the 15-year average.   It was not until February and March when the yield potential really started to express itself. Why, well there is a lot of weather between Oct to March, a lot of environmental positive and negative impacts on that final grain yield. This is the best timing to go out with approaches, models, or techniques to estimate yield potential for N rate recs.

While I am a big fan of soil testing, pre-plant soil samples for N are just a snap shot in time. But the While I am a big fan of soil testing, pre-plant soil samples for N are just a snapshot in time, but the nitrogen cycle Figure 3, will roar on after the soil sample is collected. Organic matter (OM) is the central component of this cycle and drives availability of NH4 and NO3 in the system. For each 1% OM in the top 6″ of the soil there is approximately 1000 lbs of organically bound N. The amount of N going into and out of OM pool is driven by C:N ratio of residues, soil temperature and soil moisture. While we very well what the mechanisms of the cycle are and can model the reactions quite well. Our inability to predict long term weather patterns is the greatest factor limiting our ability to predict future availability of NSoil.

Figure 3. Complete Nitrogen Cycle. http://psssoil4234.okstate.edu/lecture

This is where the reader should be asking “how can we get better site specific data” and I begin the discussion on why I have been promoting the of the Sensor Based Nitrogen Rate Calculator (SBNRC) and N-Rich strip method.

Lets talk about how the approach follows Stanford’s mechanistic approach to N management. First the Yield Potential component of the SBNRC which is related to NCrop. In effect researchers have built models over the past two decades that can correlate the NDVI collected from a sensor, such as the GreenSeeker, with the crops biomass and chlorophyll content. If given the number of days the crop has been growing it is possible to use the NDVI collected from the crop as a tool to predict final grain yield. The closer the wheat gets to hollow stem, or the corn gets to tassel, the better the prediction. One reason is that we have allowed more “environmental influence” to happen. Dr. Bill Raun, a founder of the SBNRC concept kept great discussion and data sets on his NUE.OKSTATE.edu website. On the “NUE Website on YP” he provides information on how yield prediction work while on the “NUE Website YP Library” he has not listed every algorithm created, and the math behind them, but also a recipe book for how anyone can create their own algorithm. While there are a lot post sensing stresses that can bring down final grain yield, the models that have been built and continually improved, do quite a good job on predicting final grain yield in-season. Resulting a much more site specific value for NCrop. The blog”Sensing the N-Rich Strip and Using the SBNRC” goes into a further discussion of using the online SBNRC.

That now leaves NSoil, which I will argue is at least as important as NCrop. As weather so greatly influences the nitrogen cycle it would be nice to have a weather station on every field paired with a 0-4 ft soil description which could be incorporated into a model. Given those might be out of reach we have found the the use of a reference strip, high N or low N, really provides an site specific estimate the of nitrogen the crop has access to. If the high N reference (N-Rich) strip is showing up that means the remainder of the field is N deficient. This may be due to losses or lack of mineralization, either way more N is needed. If the N-Rich strip is not evident then the crop is finding enough N outside of the reference strip to support its current growth. This could be that residual N or mineralization is high, or it could mean that crop growth and therefore N demand is low. Having the N check strip in each field allows for a season long evaluation. We can use NDVI to characterize how big or little of a response we have to N. We call this the Response Index (RI). An RI of 1.8 means that we could increase yield by 80% if we add adequate N, if the RI is 1.05 then we are looking at a potential increase of 5%. I have a previous blog which goes into the application of the reference strip. “Nitrogen Rich Strips, a Reminder

Finally we combine the two, YP and RI. By predicting the yield of the area out side the N-Rich strip we can determine environmental yield potential, YP0. Basically what can the field yield if nothing is added. We multiple YP0 by the RI to get the yield potential with added N, YPN. Then its as simple as N rate = (YPN – YP0 ) x N needed per bushel. So for example if YP0 is 40 bushel RI =2, then YPN is 80 bushel. I need to fertilize the additional 40 bushels of wheat and I can use the 2.0 N per bushel can come up with a top-dress rate of 80 lbs N per acre. We are now incorporating site specific in-season NCrop and NSoil data.

And just a reminder for those of you new to my blog, I have a lot of research documenting that it is not only OK, but often best if we wait on N application in wheat and other crops. Value of In-Season N blog.

Every step we take towards the easy button is often a step towards site specific imprecision due to the use of generalized terms or models. Depending on your goals this very well could be acceptable for your operation, but with nitrogen prices as volatile as they are, should we not be considering pushing the easy button to the side, for now. Let’s add a bit of site-specific data so that we can take advantage of the N the system may be giving us, or the yield we did not expect. Let the N-Rich Strip be that first step.

Relevant Peer Review Publications.

In-Season Prediction of Yield Potential Using Wheat Canopy Reflectance,  Agron. J. 93:131-138

Nitrogen Fertilization Optimization Algorithm Based on In-Season Estimates of Yield and Plant Nitrogen Uptake
  J. Plant Nutr. 24:885-898

Real-Time Sensing and N Fertilization with a Field Scale GreenSeeker Applicator

Identifying an In-Season Response Index and the Potential to Increase Wheat Yield with Nitrogen (pdf)

Nitrogen Response Index as a Guide to Fertilizer Management
 

Evaluation of Green, Red, and Near Infrared Bands for Predicting Winter Wheat Biomass, Nitrogen Uptake and Final Grain Yield 

Full List of NUE Publications

If you have any questions please feel free to contact me @ b.arnall@okstate.edu

Recent Weather Causing Corn (and Sorghum) Injury From Pre-emerge Herbicides

With the brief window of dry ground last week my crew went at full speed planting and applying pre-emergence. Today I am sitting at home with campus closed due to the potential to severe weather with a forecast of 4-6 inches of rain for the areas I planted. Combine the recent planting activities and limited windows for pre-emergence applications, I will not be surprised if we don’t start seeing injury in some of the sorghum that was just planted before the rains. I would also add the over the years I often see bleaching in sorghum, that looks similar to zinc and/or iron deficiency, caused by atrazine injury.  This typically occurs when atrazine is applied prior to a heavy rain. The atrazine is washed down slope and into the rows, the injury is almost always seen in low lying areas.  The crop usually grows out of it.

Atrazine injury in sorghum. Heavy rains followed application. Pic via Rick Kochenower.

Atrazine injury in sorghum. Heavy rains followed application. Pic via Rick Kochenower.

Brian A.

This article is written by Mr. Cody Daft, Field Agronomist Western Business Unit, Pioneer Hi-Bred

Have you noticed any corn leafing out underground prior to emergence? Have you seen tightly rolled leaves or plants that can’t seem to unfurl leaves and look buggy whipped? Almost all of the fields I have looked at recently have shown these symptoms in at least a portion of the field, and some fields this has been very widespread. The common denominator in all the fields I have viewed has been the herbicides applied were a metolachlor (Dual/Cinch type products) and the weather (cooler than normal, wetter than normal). Similar issues can be noted in grain sorghum to some extent.

The recent wet weather and water-logged soils have increased the possibility of corn injury from many popular soil applied herbicides. Corn growing in wet soils is not able to metabolize (degrade) herbicides as rapidly as corn growing in drier conditions. Plant absorption of herbicides occurs by diffusion. What this means is that the herbicide diffuses from locations of high concentration (application site on the soil) to low concentration (plant roots). The diffusion process continues regardless of how rapidly the corn is growing. In corn that is not growing rapidly (cool, wet conditions) corn plants can take up doses of herbicide high enough to show damage and a few differences in symptomology.

The unfortunate aspect of wet soil conditions is that additional stress is put on the plant not only to metabolize herbicide residues, but also to ward off diseases and insects. These additional stresses can impact a corn plant’s ability to metabolize herbicide.

The most common type of herbicide injury observed under these conditions is associated with chloroacetamide herbicides. These herbicides are used for control of grass and small seeded broadleaf weeds, and are seedling root and shoot inhibitors.

These products include the soil-applied grass herbicides such as:

  • Dual/Cinch/Medal II
  • Degree/Harness
  • Microtech/Lasso
  • Frontier/Outlook
  • Define/Axiom
  • And other atrazine premixes like Lumax (a premix of mesotrione (Callisto), s-metolachlor (Dual II Magnum), atrazine and a safener benoxacor).

What About The Injury Symptoms?

Before corn emergence:

  • Stunting of shoots that result in abnormal seedlings that do not emerge from soil.
  • Corkscrewing symptoms similar to cold/chilling injury.
  • Corn plants and grassy weeds may leaf out underground and leaves may not properly unfurl.

After corn emergence:

  • Buggy whipping – leaves may not unfurl properly.

buggy-whipping syndrom

Figure . Buggy-whipping symptom from carryover of PPO herbicides to corn.via https://www.pioneer.com/home/site/us/agronomy/library/herbicide-carryover/

 

 

What About Safeners?
Products like DUAL II Magnum herbicide contain the safener benoxacor which has been shown to enhance S- Metolachlor metabolism in corn. This enhanced metabolism can reduce the potential of S- Metolachlor injury to corn seedlings when grown under unfavorable weather conditions such as cool temperature or water stress. However, a safener is not the silver bullet, and slow plant growth may still have trouble metabolizing the herbicide even with a safener…but it does help the severity of damage/symptoms.

Will The Plants Recover?
Plants that have leafed out underground or show corkscrewed mesocotyl symptoms are likely to not recover or even emerge from below the soil. Larger plants that are already emerged that show tightly rolled leaves and are buggy whipped will most likely recover once the field sees drier conditions and we have warm weather and sun light to assist in better plant growth.

More Information Discussing Corn Injury From Pre-emerge Herbicides Here:

http://ipm.missouri.edu/IPCM/2009/4/Cool-Wet-Soils-Can-result-in-More-Corn-Injury-from-Preemergence-Residual-Herbicides/

 

Cody Daft
Pioneer Hi-Bred
cody.daft@pioneer.com

Poly versus Ortho another year of data from Iowa

Guest Author, Dr. Jake Vossenkemper; OkState Grad and Agronomy Lead, Liquid Grow Fertilizer

Updated Research Comparing Ortho/Poly-Phosphate Ratios for In-Furrow Seed Safe Starter Fertilizers. Last years post Link

Article Summary

  • Ortho-phosphates are 100% plant available, but a high percentage of poly-phosphates in starter fertilizers convert to ortho-phosphate within just two days of application.
  • This quick conversion from poly- to ortho-phosphate suggests expensive “high” ortho starter fertilizers are not likely to result in increased corn yields compared to seed-safe fluid starters containing a higher percentage of poly-phosphate.
  • On-farm field studies conducted near Traer, IA in the 2016 and 2017 growing season found no statistical difference (Pr > 0.05) in corn yield between conventional and high ortho-phosphate starters in either year.
  • High ortho starters cost more per acer than 50/50 ortho:poly starters, but do not increase corn grain yields.

Polyphosphates Rapidly Convert to Plant available Orthophosphates

Given polyphosphates are not immediately plant available and orthophosphates are immediately plant available, this gives the promoters of “high” orthophosphate starters ample opportunity to muddy the waters. Nevertheless, the facts are, polyphosphates are rather rapidly hydrolyzed (converted to) into orthophosphates once applied to soils, and this hydrolysis process generally takes just 48 hours or so to complete.

In September of 2015, we posted a blog discussing some of the more technical reasons why the ratio of ortho to polyphosphates in starter fertilizers should have no impact on corn yields. For those that are interested in the more technical details, we encourage you to follow this link to the September 2015 blog post.

While we was relatively certain that the ratio of ortho to polyphosphates in liquid starters should have no effect on corn yields, we decided to “test” this idea with on-farm field trials located near Traer, IA in the 2016 and 2017 growing seasons.

How the Field Trial Was Conducted

In these field trials, we used two starters applied in-furrow at 6 gal/ac. Each starter had an NPK nutrient analysis of 6-24-6. The only difference between these two starters was the ratio of ortho to polyphosphates. One of these starters contained 80% orthophosphate and the other contained just 50% orthophosphate. With the remainder of the phosphorus source in each of these two starters being polyphosphate. Each plot was planted with a 24-row planter (Picture 1) and was nearly 2400 ft long. In both the 2016 and 2017 growing seasons the experimental design used was a randomized complete block with 4 or 5 replications.

Field Trial Results

Averaged over the side-by-side replications there was less than 1 bu/ac difference in corn grain yield between the high ortho and low ortho polyphosphate starters in both the 2016 and 2017 growing seasons. In addition to finding no differences in grain yield between these two starters, the high ortho starters generally cost about $1 more per/gal (so the $6/ac difference in price at a 6 gal/ac rate) than the low ortho starters. So the more expensive high ortho starter clearly did not “pay” its way in our multi-year field trials.

More Trials Planned for 2018

While our findings agree with other research-comparing ortho and polyphosphate starter fertilizers (Frazen and Gerwing. 1997), we want to be absolutely certain that our fertilizer offerings are the most economically viable products on the market. Therefore, we have decided to run this same field trial at one location in northern, IL in 2018, and at one location in central, IA in 2018. Stay tuned for those research results next fall.

References
Franzen D. and J. Gerwing. 2007. Effectiveness of using low rates of plant nutrients. North Central regional research publication No. 341. http://www.extension.umn.edu/agriculture/nutrient-management/fertilizer-management/docs/Feb-97-1.pdf (accessed 8 of Sept 2015).

A big Thank You to Dr. Vossenkemper for sharing this article with us.
The original article and his contact can be found at Link

Time to re-post an old post. Sorghum injuries from Pre-Emerge Herbicides

Based on a few recent text messages and emails I think it is time to revisit an older post about Corn and Sorghum injuries from pre-plant herbicides.

Direct link to the original post  Recent Weather Causing Corn (and Sorghum) Injury From Pre-emerge Herbicides

Sorghum with likely atrazine injury. Image courtesy Jana Slaughter 

 

Comparing Ortho/Poly-Phosphate Ratios for In-Furrow Seed Safe Starter Fertilizer

Guest Author, Dr. Jake Vossenkemper; Agronomy Lead, Liquid Grow Fertilizer

New Research Comparing Ortho/Poly-Phosphate Ratios for In-Furrow Seed Safe Starter Fertilizers

Article Summary

  • Ortho-phosphates are 100% plant available, but a high percentage of poly-phosphates in starter fertilizers convert to ortho-phosphate within just two days of application.
  • This quick conversion from poly- to ortho-phosphate suggests expensive “high” ortho starter fertilizers are not likely to result in increased corn yields compared to seed-safe fluid starters containing a higher percentage of poly-phosphate.
  • A field study conducted near Traer, IA in the 2016 growing season found less than 1 bu/ac yield difference between a 50/50 ortho:poly starter and high ortho-phosphate starter.
  • High ortho starters cost more per acer than 50/50 ortho:poly starters, but do not increase corn grain yields.

Poly-phosphates Rapidly Convert to Plant available Ortho-Phosphates

Given poly-phosphates are not immediately plant available and ortho-phosphates are immediately plant available, this gives the promoters of “high” ortho-phosphate starters ample opportunity to muddy the waters. Nevertheless, the facts are that poly-phosphates are rather rapidly hydrolyzed (converted to) into ortho-phosphates once applied to soils, and this hydrolysis process generally takes just 48 hours or so to complete.

In Sept. of 2015, I posted a blog discussing some of the more technical reasons why the ratio of ortho- to poly-phosphates in starter fertilizers should have no impact on corn yields. For those that are interested in those more technical details, I encourage you to follow this link to the Sept. 2015 blog post: https://www.liqui-grow.com/farm-journal/.

While I was relatively certain that the ratio of ortho- to poly-phosphates in liquid starters should have no effect on corn yields, I decide to “test” this idea with a field trial in the 2016 growing season conducted near Traer, IA.

How the Field Trial Was Conducted

In this field trial, we used two starter products applied in-furrow at 6 gal/ac. Each starter had an NPK nutrient analysis of 6-24-6. The only difference between these two starters was the ratio of ortho- to poly-phosphate. One of these starters contained 80% ortho-phosphate and the other contained just 50% ortho-phosphate with the remainder of the phosphorous source in each of these two starters being poly-phosphate. Each plot was planted with a 24-row planter (Picture 1) and plot lengths were nearly 2400 ft. long. In total, there were 5 side-by-side comparisons of the two starter fertilizers that contained different ratios of ortho- to poly-phosphates.

Field Trial Results

In general, there were no large differences in yield between the two starters in any of the 5 side-by-side comparisons, except for comparison number 5 (Figure 1). In comparison number 5, the 50% ortho/50% poly-phosphate starter actually yielded 6 bu/ac more than the high ortho starter. But averaged over the 5 side-by-side comparisons, there was less than 1 bu/ac yield difference between the high and low ortho starters (P=0.6712).

In addition to finding no differences in grain yield between these two starters, the high ortho starters generally cost about $1 more per gallon (so $6/ac at a 6 gal/ac rate) than the low ortho starters. So the more expensive high ortho starter clearly did not “pay” its way in our 2016 field trial.

More Trials Planned for 2017

While our findings agree with other research-comparing ortho- and poly-phosphate starter fertilizers (Frazen and Gerwing. 1997), we want to be absolutely certain that our fertilizer offerings are the most economically viable products on the market. Therefore, I have decided to run this same field trial at one location in northern Illinois in 2017, and at one location in central Iowa in 2017. Stay tuned for those research results this fall.

Picture 1
Planting starter fertilizer trials near Traer, IA in the growing season of 2016.

 

 

 

 

 

 

 

 

 

5 side-by-side comparisons of corn yield from two 6-24-6 starter fertilizers that contained either 50% ortho & 50% poly-phosphate or 80% ortho and 20% poly-phosphate. The field trial was conducted near Traer, IA in the growing season of 2016.

 

 

 

 

 

 

 

 

 

 

 

 

 

References

Franzen D. and J. Gerwing. 2007. Effectiveness of using low rates of plant nutrients. North Central regional research publication No. 341. http://www.extension.umn.edu/agriculture/nutrient-management/fertilizer-management/docs/Feb-97-1.pdf (accessed 8 of Sept 2015).

The Sufficiency versus Replacement tipping point.

Being educated in the realm of Soil Fertility at Oklahoma State University by the likes of Dr Gordon Johnson and Dr. Bill Raun, Brays Nutrient Mobility Concept and Mitscherlich’s Percent Sufficiency Concept are ingrained in my psyche. In class the concept of Build and Maintain for phosphorus fertilizer management was just briefly visited and not discussed as a viable option.  For anyone in the corn belt, and some Okies, reading this that may seem unusual.  But when I was in school on average in Oklahoma there was about 100-200 K acres of 100 120 bpa (bushel per acre) corn, 300-400 K acres of 40-50 bpa sorghum, and over 5 million acres of 20-30 bpa wheat.  In a state with those average yields, replacing P removed by the crop was not a major concern.

But times are changing.  There is more corn and soybean planted and the achievable yields of all crop are increasing.  While the average winter wheat producer should not be worried about replacement rates of P there is a growing group of producers that should.  This blog will discuss the scenarios in which sufficiency rates are best and those in which replacement should be considered. The OSU factsheet PSS-2266 goes in-depth on each of these methods.

Applying P based on sufficiency will increase soil test P levels in a low yielding environment.  For example on a 20 bpa wheat field that starts out with a soil test P level of 0. Using the sufficiency recommendation each year the soil test value will reach 20 ppm (40 STP) in 20 years. A 30 bpa field would take 30 years.  Yes that is a long time but the soil test value is increasing a little each year. The point of 20 ppm is important because at that level the crop is 95% sufficient, meaning if no P is added the crop will only reach 95% of the fields yield potential.

Using a mass balance approach we can determine at what point does the crop remove more than we can supply with in or near furrow starter fertilizer.  Table 1 shows the values I am using for the discussion.  The first column is just the average amount of P removed per bushel of grain, most of our grains fall in the .4 to .5 lbs P per bushel range.  The second column is the soil test value at which P level is said to be at 90% sufficient. The reason this column is included is that the P2O5 reccomendation for this P level fits into the starter rate for all crops. The low high starter rates are the typical range of P2O5 that is delivered within the safe range (N based) and what I see as the common rates.  These values may be above or below what you use. 

Values used to create Table 2. Phosphorus per bushel of grain. Mehlich 3 soil test value (ppm) at which crop is determined to be 90% sufficient, typical range of P2O5 applied with starter fertilizers, recommended P2O5 rate when soil test P is at 90% sufficiency.

Table 1. Values used to create Table 2. Phosphorus per bushel of grain. Mehlich 3 soil test value (ppm) at which crop is determined to be 90% sufficient, typical range of P2O5 applied with starter fertilizers, recommended P2O5 rate when soil test P is at 90% sufficiency.

 

Table 2 is pretty simple but it is the center point of this article.  The one caveat I need to add is this assumes strip till or 2*2 / 3*2 is not being used. Table 2 is using the starter range and removal value to determine the yield level the starter can support. The first take on this table may provide some hint on why in a state with 5 million acres of wheat averaging 36 BPA the state soil fertility specialist didn’t focus on replacement rates.  In fact for most for most the the wheat ground P application is higher than removal and P levels are slowly increasing. The big take home from this table should be is my yield level outside this window? If so do not immediately go out in crease your P rates but do take a close look at your system as a whole.  Take a close look at your cropping system, not just one seasons but look at a three or four year cycle.  Add up P applied and P removed, are you positive or negative net balance?  If you are negative take a long hard look at your soil test over time.  Some soils can supply a large amount of P even if you are removing more than you apply.  Other soils will be rapidly drawn down.  Regualr soil testing allows for producers to keep an eye on these values. 

Yield level (bushels per acre) at which P removal is equal to P added in starter fertilizer application.

Table 2. Yield level (bushels per acre) at which P removal is equal to P added in starter fertilizer application.

 

In the end even if the production warrants the use of replacement rates, the current market may not. For more on that read https://osunpk.com/2016/08/27/now-may-not-be-the-time-for-replacement/.

Speaking of market currently both soybeans and cotton are getting a lot of attention due to how the economics is penciling out. Soybean is a “heavy” P crop pulls .8 lbs per bpa while cotton removes 13 lbs per bales. Both of these crops are salt sensitive and the rate of inforrow is typically quite low providing only about 6 lbs when on 30″ rows.  If you are growing beans or cotton make sure you account for their removal when you talley up your system. 

 Below is a table that I wanted to add, well because I like it. This table illustrates that buildup, and drawdown, rate is heavily impacted by existing soil test value.  In short it takes a lot more fertilizer P to raise soil test p levels in a very low P testing field than it does when soil test P is closer to optimum, 19 lbs per 1 lb at STP of 10 and 5 lbs per lb when STP is 65.  The exact rate changes by soil type and the same holds true to drawn down via crop removal. 

Amount of P2O5 above crop removal needed to increase soil test phosphorous based upon intital soil test results. Adapted From http://www.spectrumanalytic.com/support/library/ff/Soil_test_P_and_K_buildup_and_drawdown.htm "Drawdown of Soil Test Phosphorus and Potassium Levels by Alfalfa, K.L. Wells & J.E. Dollarhide, Univ. of Kentucky, Soil Science News & Views, Vol. 21, No. 3, 2000"

Amount of P2O5 above crop removal needed to increase soil test phosphorous based upon initial soil test results.
Adapted From http://www.spectrumanalytic.com/support/library/ff/Soil_test_P_and_K_buildup_and_drawdown.htm “Drawdown of Soil Test Phosphorus and Potassium Levels by Alfalfa, K.L. Wells & J.E. Dollarhide, Univ. of Kentucky, Soil Science News & Views, Vol. 21, No. 3, 2000”

 

 Any questions or comments? Feel free to contact me at b.arnall@okstate.edu

 

Recent Weather Causing Corn (and Sorghum) Injury From Pre-emerge Herbicides

While this is not about fertility in the southern Great Plains I feel it is a very important topic.  I will not be surprised if we don’t start seeing this in some of the corn and sorghum that was just planted before the rains. I would also add the over the years I often see bleaching in sorghum, that looks similar to zinc and/or iron deficiency, caused by atrazine injury.  This typically occurs when atrazine is applied prior to a heavy rain. The atrazine is washed down slope and into the rows, the injury is almost always seen in low lying areas.  The crop usually grows out of it.

Atrazine injury in sorghum. Heavy rains followed application.  Pic via Rick Kochenower.

Atrazine injury in sorghum. Heavy rains followed application. Pic via Rick Kochenower.

Brian A.

This article is written by Mr. Cody Daft, Field Agronomist Western Business Unit, Pioneer Hi-Bred

Have you noticed any corn leafing out underground prior to emergence? Have you seen tightly rolled leaves or plants that can’t seem to unfurl leaves and look buggy whipped? Almost all of the fields I have looked at recently have shown these symptoms in at least a portion of the field, and some fields this has been very widespread. The common denominator in all the fields I have viewed has been the herbicides applied were a metolachlor (Dual/Cinch type products) and the weather (cooler than normal, wetter than normal). Similar issues can be noted in grain sorghum to some extent.

The recent wet weather and water-logged soils have increased the possibility of corn injury from many popular soil applied herbicides. Corn growing in wet soils is not able to metabolize (degrade) herbicides as rapidly as corn growing in drier conditions. Plant absorption of herbicides occurs by diffusion. What this means is that the herbicide diffuses from locations of high concentration (application site on the soil) to low concentration (plant roots). The diffusion process continues regardless of how rapidly the corn is growing. In corn that is not growing rapidly (cool, wet conditions) corn plants can take up doses of herbicide high enough to show damage and a few differences in symptomology.

The unfortunate aspect of wet soil conditions is that additional stress is put on the plant not only to metabolize herbicide residues, but also to ward off diseases and insects. These additional stresses can impact a corn plant’s ability to metabolize herbicide.

The most common type of herbicide injury observed under these conditions is associated with chloroacetamide herbicides. These herbicides are used for control of grass and small seeded broadleaf weeds, and are seedling root and shoot inhibitors.

These products include the soil-applied grass herbicides such as:

  • Dual/Cinch/Medal II
  • Degree/Harness
  • Microtech/Lasso
  • Frontier/Outlook
  • Define/Axiom
  • And other atrazine premixes like Lumax (a premix of mesotrione (Callisto), s-metolachlor (Dual II Magnum), atrazine and a safener benoxacor).

What About The Injury Symptoms?

Before corn emergence:

  • Stunting of shoots that result in abnormal seedlings that do not emerge from soil.
  • Corkscrewing symptoms similar to cold/chilling injury.
  • Corn plants and grassy weeds may leaf out underground and leaves may not properly unfurl.

After corn emergence:

  • Buggy whipping – leaves may not unfurl properly.

buggy-whipping syndrom

Figure . Buggy-whipping symptom from carryover of PPO herbicides to corn.via https://www.pioneer.com/home/site/us/agronomy/library/herbicide-carryover/

 

 

What About Safeners?
Products like DUAL II Magnum herbicide contain the safener benoxacor which has been shown to enhance S- Metolachlor metabolism in corn. This enhanced metabolism can reduce the potential of S- Metolachlor injury to corn seedlings when grown under unfavorable weather conditions such as cool temperature or water stress. However, a safener is not the silver bullet, and slow plant growth may still have trouble metabolizing the herbicide even with a safener…but it does help the severity of damage/symptoms.

Will The Plants Recover?
Plants that have leafed out underground or show corkscrewed mesocotyl symptoms are likely to not recover or even emerge from below the soil. Larger plants that are already emerged that show tightly rolled leaves and are buggy whipped will most likely recover once the field sees drier conditions and we have warm weather and sun light to assist in better plant growth.

More Information Discussing Corn Injury From Pre-emerge Herbicides Here:

http://ipm.missouri.edu/IPCM/2009/4/Cool-Wet-Soils-Can-result-in-More-Corn-Injury-from-Preemergence-Residual-Herbicides/

 

Cody Daft
Pioneer Hi-Bred
cody.daft@pioneer.com