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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.

Its dry and nitrogen cost a lot, what now?

The title says a lot about the primary question I am receiving right now. And the latest long range “forecast” does not make me feel any better about the current situation. But it is what it is and many great plains wheat farmers are having to make a decision.

The current situation in the wheat belt is that we are dry to depth, when the 32 inch PAW is on short supply and this comes from a combination of no rain and above average temperatures.

Average 32-inch Plant Available Water. Graph retrieved from Mesonet on January 20th, 2022.
120-Day rainfall accumulation across Oklahoma. Graph retrieved from Mesonet on January 20th, 2022. Start data of this time frame is September 22, 2021
The daily average temperature departure from the 15 year mean temperature for the Lahoma Research Station. The Mesonet long-term averages utilize 15 years of daily data (e.g. daily average, daily maximum/minimum, or daily total) for every current and past Oklahoma Mesonet station.

Fertilizer prices are holding fairly strong, at expensive, and the wheat crop currently seems to be going in reverse. So what is a wheat farmer to do? If we are looking on the bright side the lack of moisture in the surface will help reducing any potential losses through urea volatilization. It does not make the potential for loss zero though. If I am bound and determined to fertilize now, I would be very selective of the source and method of application. The biggest driver, tillage and residue amounts.

  • Conventional Till / No residue (plenty of bare soil showing) and small wheat-
    • UAN via Streamer nozzles
      • Why: With UAN (urea ammonium nitrate) you have a liquid N source that will get onto and into the soil and readily available nitrate. Streaming on will help concentrate the fertilizer and potential reduce any urea volatilization if any dews were to occur. Urea would sit until dissolved and lead to potential losses if the first moisture was heavy dew and not a incorporating rainfall.
  • No-till / high residue (no bare soil showing)-
    • Dry Urea
      • Why: If Our residue is dry when the urea is spread the wind will help push it below the residue surface providing protection until a good rain. If UAN is applied to this dry or even slightly damp residue and not washed off with a rainfall in a week or so the amount of N tied up in that residue will likely be significant.
  • The big wheat (very little bare soil, lots of wheat tissue.
    • Urea or UAN Streamer
      • Why not Flat fan. At least with the current status the wheat is not growing and bigger wheat has increasing levels of tip die back. So while UAN sprayed on actively growing wheat can be absorbed foliarly, stressed wheat can not do it as well. Plus the UAN that hits dead or damaged tissue will not make it into the plant. The UAN applied via flat fan will need incorporation via rain in a couple days.

You may have caught in the paragraph above I said, “If I was bound and determined”. If I had the option I am not pulling the trigger until after I have received some good moisture. I fully expect and have already seen rigs running before every decent chance of rain. Unfortunately many of those chances have not panned out and that will remain my concern moving forward. I want to make sure we have some water in the tank before investing in the system.

But now we increase the risk/fear by waiting and the question I get is what if we don’t get good rains or don’t get good incorporating rains. The short answer is, if we don’t get rains the N application is the least of our concerns. If we approach March 15th and we have not had the rains needed to put a little water in the tank and incorporate the N then we are not likely looking at a bumper crop which will need N. What survives in that scenario will be living off deep soil water, and where there is deep soil water there is a good chance of deep N. The shallow soils will be so stressed that nutrient demand will be very little.

Now lets talk waiting and applying N. How late before we just say we are done. To answer I am going to draw from a data set I talk about a lot, the delayed N work by Dr. Souza. This study was started in the fall of 2016 and concluded with the 2020 wheat harvest. In all, twelve trials were established and achieved maturity. This study was designed to evaluate the recovery of winter wheat grain yield and protein after the crop was N stressed. Treatments included an untreated check, pre-plant application and ten in-season treatments. The application of in-season treatments was initiated when N deficiency was confirmed and treatments were applied in progressive order every seven growing days to the point of 63 growing days after visual deficiency (DAVD). A growing degree days is any day that the average daily temperature is at or above 40⁰ F.  Ammonium nitrate (NH4NO3) was applied at a rate of 90 lbs N ac-1 for all treatments.

With this data we can answer two questions, first at what point did we lose yield compared to pre-plant and second how late could we apply and still increase yield above the check. So comparing to the pre lets us know how long could we wait with losing yield. Across the trials we lost yield three times by waiting too long, at LCB2017b that was 4/19, Lahoma18 it was around 3/30, and then Newkirk2020 we lost yield by waiting until 4/6. This data is why I am pretty comfortable waiting until mid March when and if needed. Now if we look at the check, that will tell us if things start improving late can we get still get a yield bump with added N. Newkirk 2020 was the only time and place we could increase yield above the zero after the 4/14 additions.

Table 1. Date of nitrogen application. Each month is color coded.
Table 2. Evaluation of winter wheat grain yield and protein results compared to the Pre-plant Nitrogen treatment. Red boxes means the treatment yielded statistically lower results, Yellow is no difference, Green means the treatment has increased grain yield or protein. Perkins2018, LSC2018b, and LCB2019, did not have a grain yield respond to N (no red box in Zero check) and therefore will not be discussed.

Take Home Message

My recommendation is that if you are not required to take delivery or needing to cover a lot of acres, i.e. time limited, I would not get in a hurry to apply N on this wheat crop. I think if we combine weather by market this a good time to wait and see. Once we get a rain and have some soil moisture it will be time to run the rigs. The crop currently does not need a lot of N so why spend the $. If things don’t improve by mid to late march, consider the wheat a cover and look towards a summer crop with the hopes of rains in April. If you need to take the crop to yield, then you can wait a while longer and still get a return on the N, with hopes the price could come down a bit.

Finally, While I don’t suggest running fertilizer in front of the first chance of rain, I would make sure I had an N-Rich strip on each and every single field. Strips can go out well past green up and serve a great purpose. The N-Rich strip will help you determine if the crop is able to mine any soil N or if the N tank is dry.

Feel free to reach out with questions or comments.
Brian Arnall Precision Nutrient Management Specialist.
b.arnall@okstate.edu

Special thanks to EDC Ag Products Co LLC for suppling NH4NO3 used in the delayed N project.

Relevant past blogs for your reading enjoyment.

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

Banding P as a band-aid for soil acidity, not so cheap now.

Whoi Cho, PhD student Ag Economics advised by Dr. Wade Brorsen
Raedan Sharry, PhD Student Soil Science advised by Dr. Brian Arnall
Brian Arnall, Precision Nutrient Management Extension.

In 2014 I wrote the blog Banding P as a Band-Aid for low-pH soils. Banding phosphate to alleviate soil acidity has been a long practiced approach in the southern Great Plains. The blog that follows is a summary of a recent publication that re-evaluated this practices economic viability.

Many Oklahoma wheat fields are impacted by soil acidity and the associated aluminum (Al) toxicity that comes with the low soil pH. The increased availability of the toxic AL3+ leads to reduced grain and forage yields by impacting the ability of the plant to reach important nutrients and moisture by inhibiting root growth. Aluminum can also tie up phosphorus in the soil, further intensifying the negative effects of soil acidity. More on the causes and implication of soil acidity can be found in factsheet PSS-2239 or here (https://extension.okstate.edu/fact-sheets/cause-and-effects-of-soil-acidity.html). The acidification of many of Oklahoma’s fields has left producers with important choices on how to best manage their fields to maximize profit.

Wheat Trial, Cimarron Valley Research Station

Two specific management strategies are widely utilized in Oklahoma to counter the negative impacts of soil acidification: Lime application and banding phosphorus (P) fertilizer with seed. While banding P with seed ties up Al allowing the crop to grow, this effect is only temporary, and application will be required every year. The effects of liming are longer lasting and corrects soil acidity instead of just relieving Al toxicity. Historically banding P has been a popular alternative to liming largely due to the much lower initial cost of application. However, as P fertilizers continue to increase in cost the choice between banding P and liming needed to be reconsidered.

A recent study by Cho et al.,2020 compared the profitability of liming versus banding P in a continuous wheat system considering the impacts that lime cost, wheat price and yield goal has on the comparison. This work compared the net present value (NPV) of lime and banded P.  The study considered yield goal level (40 and 60 bu/ac) as well as the price of P2O5 fertilizer and Ag Lime. The price of P2O5 used in this study was $0.43 lb-1 while lime price was dictated by distance from quarry, close to quarry being approximately $43 ton-1  and far being $81 ton-1. For all intents and purposes these lime values are equivalent to total lime cost including application. Wheat prices utilized in the study were $5.10 bu-1  and $7.91 bu-1. It is important to note that baseline yield level was not considered sustainable under banded P management in this analysis. This resulted in a decrease in yield of approximately 3.2 bu ac-1  per year. This is attributable to the expected continued decline in pH when banding P is the management technique of choice.

The analysis in this work showed that lime application is cost prohibitive in the short term (1 year) when compared with banding P regardless of lime cost, yield goal level, and wheat value (within the scope of this study). This same result can be seen over a two-year span when yield is at the lower level (40 bu ac-1). While in the short-term banding P was shown to be a viable alternative to liming, as producers are able to control ground longer lime application becomes the more appealing option, especially when producers can plan for more than 3 years of future production. In fact, under no set of circumstances did banding P provide greater economic return than liming regardless of crop value, yield, or liming cost when more than 3 years of production were considered and only under one scenario did banded P provide a higher NPV in a 3-year planning horizon.

While historically banding P was a profitable alternative to lime application for many wheat producers the situation has likely drastically changed. At the time of writing this blog (09/17/2021) Diammonium Phosphate (DAP) at the Two Rivers Cooperative was priced at $0.78 lb-1. of P2O5. This is a drastic increase in P cost over the last year or so since Cho et al. was published in 2020. With P fertilizer prices remaining high it will be important for producers to continue to consider the value of liming compared to banded P. This is particularly crucial for those producers who can make plans over a longer time frame, especially those more than 3 years.

Addendum: As fertilizer prices have continued to rise a quick analysis utilizing the $0.78 lb-1 of P2O5was completed to consider the higher P fertilizer cost. Under this analysis an estimated decrease in NPV of approximately $38 an acre for P banding occurred. When considering this change in NPV, lime application becomes the more profitable option for alleviation of soil acidity symptoms even in the short term (assuming lime price values are equivalent to the previous analysis). This underlines the fact that it is imperative to consider the impact on profitability of the liming vs. banding P decision in the current economic climate for agricultural inputs.

Link to the Open Access Peer Reviewed publication “Banding of phosphorus as an alternative to lime for wheat in acid soil” https://doi.org/10.1002/agg2.20071

Split N application pays in graze out wheat.

Bronc Finch Ph.D. student under the leadership of D.B. Arnall
Brian Arnall, Precision Nutrient Management Specialist.

A study conducted by Oklahoma State University, in cooperation with Noble Research Institute has had the opportunity to evaluate the nitrogen management of graze-out winter wheat over the past three years. This study was set up with three nitrogen management treatments of a 60 lb N pre-plant, 120 lb N pre-plant and a split application with 60 lbs N at pre-plant and 60 lbs N at spring top-dress applications. In the 2018-2019 season top-dress N was applied shortly after Feekes 6 stage (hollow-stem) due to rain and other conditions preventing timely top-dress. The 2019-2020 and 2020-2021 growing seasons received ideally timed top-dress applications in late February to early March. For this study the first cuttings were targeted for just before the appearance of first hollow stem, and second harvest was targeted at just prior to boot stage. The 2020-2021 growing season had much less growth at the time of top-dress than previous years due to a severe early spring freeze damage which resulted in only a harvest at boot.

Spreading top-dress nitrogen on the graze-out wheat studies

Table 1. Rainfall totals for each year within each location. September 1 – January 1 represents the pre-vernalization grazing period, September 1 – January 1 represents the growing season total.

Crop production can be majorly impacted by the environment, and that is no different for a forage production system such as in this study. Table 1 shows the differences in rainfall totals for each growing season, and how much of that seasons total fell prior to January when hard freezing conditions typically occur. The 2018-2019 season saw at least 40% more rainfall than other years at both location. Much of this increase was in the fall and early winter which lead to a greater first harvest at both locations and greater soil moisture storage for after spring green-up. The environmental impacts continue to cause reduction in annual yields for the 2020-2021 season with a longer cool season and a late freeze (data not shown) which caused significant winter kill on what was a decent fall production.

Figure 1. Gain-yield production (dry matter yield * net energy for gain)in tons per acre, for each N rate application; 60 lbs of N pre-plant, 120 lbs of N pre-plant and a split application (60-60) of 60 lbs of N pre-plant and 60 lbs of N top-dress. These are presented for each location Chickasha (Left) and Lake Carl Blackwell (Right). Each season gain-yield is denoted by the value within each bar and the system total is denoted by the value above each bar.

Regardless of environmental impacts system improvements were observed with the management on N for wheat biomass production. Figure 1 shows the amount of biomass that can be attributed to the gain of a grazing animal, calculated as dry matter yield * net energy for gain. Gain-yield production reported substantial increases in total system production with the increase in N rate in comparison to a lower 60 lb per acre rate. When forage dry matter yields were near or above 5 tons, such as in 2018-2019 the split application of 60 lbs pre-plant and 60 lbs top dress significantly increased the yield and gain-yield, while lower yielding years only saw increases with increased rate. Overall system production improved with the increase of application and slight improvements were reported when application of N was closer to plant utilization.

Figure 2.  Nitrogen Uptake in pounds per acre, for each N rate application; 60 lbs of N at pre-plant, 120 lbs of N pre-plant and a split application (60-60) of 60 lbs of N pre-plant and 60 lbs of N top-dress. These are presented for each location Chickasha (Left) and Lake Carl Blackwell (Right). Each season N uptake is denoted by the value within each bar and the system total is denoted by the value above each bar.

Total N uptake of harvested biomass is documented in Figure 2 and follows a similar trend as total biomass yield. Total N uptake can be directly related to protein, as protein is total N * 6.25. As observed with the total biomass production, N uptake was reduced annually due to the reduction in available soil moisture and plant growth. The increase of rate increased overall system N uptake as well as increased annual N uptake. Split applications of N resulted in an increased N uptake in comparison to the same total rate applied as pre-plant for the entire system and in most individual years. Increasing the uptake of N not only leads to the increase in biomass and protein concentration but also allows for the more efficient usage of fertilizers. By utilizing as much fertilizer as possible allowing for increased root growth to mine N from the soil. These increases in yield production and nitrogen uptake improve the gain potential of the forage crop which leads to increases in return on investment for the producer.

Spring harvest of the graze out wheat fertility study.

Net returns can be calculated by multiplying gain by cattle price. Table 2 shows the 3-year Gain, Return, and Profit of the 120 pre and 60-60 split treatment. The dollar value of gain was set at $1.12 per pound as reported by Dr. Derrell Peel in the Cow-Calf Corner August 16, 2021 newsletter. Interestingly, the delay of the additional 60 lbs N until a top-dress application results in an average increase of $458 per acre over the 120-pre-plant rate. This increase in profit does take into account the extra application cost of top-dress. The rate used was $7.82 ac-1 per year: OSU Fact sheet “CR-230. This results in an increased cost of $23.46 over a three year time frame.

Table 2. Evaluation of Gain (dry matter yield * net energy for gain) in tons ac-1, Return (Gain * $1.12) in $ ac-1, Profit (Return minus fertilizer and application cost $241.03 for 120 and $264.49 for 60-60 split) and the Difference between the profit of 120 lbs of N applied preplant and the 60-60 split application.

As the winter wheat planting begins and decisions are being made, the management of nitrogen can be a very challenging one. From this data set, yield increased with the application of N above 60 lbs, as expected. While the decision to pre-plant or split apply can add an element of difficulty to the decision, the split application has been shown to be equal to or better than 100% pre-plant application. This study indicates the application of a split of N can be more profitable, than utilizing a pre-plant application of the same rate. Resulting in improved livestock gain-yield production, and system profitability. While the split application did not have a big payoff every year, taking advantage of it in the good years resulted in such a significant increase that split application resulted in a $458 per acre increase in profit across the two sites.

For questions or comments please feel free to reach out.
Brian Arnall
b.arnall@okstate.edu
405.744.1722

Acknowledgement of the support by Noble Research Institute for this project.

In-furrow fertilizers for wheat

From Guest Author, Dr. Dorivar Ruiz Diaz, Nutrient Management Specialist, Kansas State University

Wheat is considered a highly responsive crop to band-applied fertilizers, particularly phosphorus (P). Application of P as starter fertilizer can be an effective method for part or all the P needs. Wheat plants typically show a significant increase in fall tillers (Figure 1) and better root development with the use of starter fertilizer (P and N). Winterkill can also be reduced with the use of starter fertilizers, particularly in low P testing soils.

Figure 1. Effects on wheat tillering and early growth with in-furrow P fertilizer on soil testing low in P. Photo taken in 2020 in Manhattan, KS. Photo by Chris Weber, K-State Research and Extension.

In-furrow fertilizer application

Phosphorus fertilizer application can be done through the drill with the seed. In-furrow fertilizer can be applied, depending on the soil test and recommended application rate, either in addition to or instead of, any pre-plant P applications. The use of dry fertilizer sources with air seeders is a very popular and practical option. However, other P sources (including liquid) are agronomically equivalent and decisions should be based on cost and adaptability for each operation.

When applying fertilizer with the seed, rates should be limited to avoid potential toxicity to the seedling. When placing fertilizer in direct contact with wheat seed, producers should use the guidelines in Table 1.

Table 1. Suggested maximum rates of fertilizer to apply directly with the wheat seed

 Pounds N + K2O (No urea containing fertilizers)
Row spacing
(inches)
Medium-to-fine
soil textures
Course textures or dry soils
 
151611
102417
6-83021

Air seeders that place the starter fertilizer and seed in a 1- to 2-inch band, rather than a narrow seed slot, provide some margin of safety because the concentration of the fertilizer and seed is lower in these diffuse bands. In this scenario, adding a little extra N fertilizer to the starter is less likely to injure the seed – but it is still a risk.

What about blending dry 18-46-0 (DAP) or 11-52-0 (MAP) directly with the seed in the hopper? Will the N in these products hurt the seed?

The N in these fertilizer products is in the ammonium-N form (NH4+), not the urea-N form, and is much less likely to injure the wheat seed, even though it is in direct seed contact. As for rates, guidelines provided in the table above should be used. If DAP or MAP is mixed with the seed, the mixture can safely be left in the seed hopper overnight without injuring the seed or gumming up the works.  However, it is important to keep the wheat mixed with MAP or DAP in a lower relative humidity.  A humidity greater than 70% will result in the fertilizer taking up moisture and will cause gumming or caking within the mixture.  

How long can you allow this mixture of seed and fertilizer to set together without seeing any negative effects to crop establishment and yield?

The effects of leaving DAP fertilizer left mixed with wheat seed for various amounts of time is shown in Figure 2. Little to no negative effect was observed (up to 12 days in the K-State study).

Figure 2. Effects on wheat yield from mixing P fertilizer with the seed. Study conducted in 2019 and 2020 at four sites. Graph by Chris Weber, K-State Research and Extension.

Although the wheat response to these in-furrow fertilizer products is primarily from the P, the small amount of N that is present in DAP, MAP, or 10-34-0 may also be important in some cases. If no pre-plant N was applied, and the soil has little or no carryover N from the previous crop, the N from these fertilizer products could benefit the wheat.

Dorivar Ruiz Diaz, Nutrient Management Specialist
ruizdiaz@ksu.edu

Chris Weber, former Graduate Research Assistant, Soil Fertility

Nitrogen Rich Strips, a Reminder

With the recent increase in fertilizer prices just prior to winter wheat planting season I felt it was a good opportunity to bring this older post back up and give it an update. Since the blog was originally written in 2013 there has been a lot of work done both to better understand the nitrogen fertilizer need / timing of winter wheat and efforts to updated and improve the algorithms behind the Sensor Based Nitrogen Rate Calculator.

The Nitrogen Rich Strip, or N-Rich Strip, is a technique/tool/process that I spend a great deal of time working with and talking about.  It is one of the most simplistic forms of precision agriculture a producer can adopt.  The concept of the N-Rich strip is to have an area in the field that has more nitrogen (N) than the rest.  In recent years we have been utilizing Zero-N strips in corn. The approach to some may be new but at one point most producers have had N-Rich Strips in their fields, albeit accidentally.  Before the days of auto-steer it was not uncommon, and honestly still is not, to see a area in the field that the fertilizer applicator either doubled up on or skipped.  In our pastures and dual purpose/graze out wheat every spring we can see the tell-tale signs of livestock deposits.  When over laps or “Cow Pox” become visible we can assume the rest of the field is behind in nitrogen.  The goal of an N-Rich Strip is to let the field tell you when it needs more N. Research has shown wheat can be yellow and recover completely and it may even be a benefit. See the link for the Value of In-season Nitrogen at the end of this blog.

Cow Pox, Image courtesy Kaitlyn Nelson
Cow Pox, Image courtesy Kaitlyn Nelson

What I like most about the N-Rich Strip approach is its Simplicity.  The N-Rich Strip is applied and; Scenario 1. The N-Rich Strip becomes visible (Greener) you APPLY NITROGEN, Scenario 2.  The strip is not visible you Option A. DON’T APPLY NITROGEN Option B. Apply Nitrogen Anyways.  The conclusion to apply N or not is based on the reasoning that the only difference between the N-Rich Strip and the area 10 ft from it is nitrogen, so if the strip is greener the rest of the field needs nitrogen.  If there is no difference N is not limiting and our research shows N does not have to be applied.  However producers who decide to be risk adverse (in terms of yield) can apply N but it would be advised to do so at a reduce the rate.  Now is a good time to note that the N-Rich Strip alone provides a Yes or No, not rate recommendation.  At OSU we use the GreenSeeker optical sensor and Sensor Based Nitrogen Rate Calculator (SBNRC) to determine the rate, but that discussion will come later.  I equate the change from using yield goal N rate recs to the N-Rich Strip as to going from foam markers to light bars on a sprayer.   Not 100% accurate but a great improvement.

N-Rich Strip in no-till wheat near Hobart OK.
N-Rich Strip in no-till wheat near Hobart OK.
N-Rich Strips showing up on google earth image. You can see how the strip on the left is darker than the right suggested a greater need for nitrogen.

Now that we have covered the WHY, lets get down to the nuts and bolts HOW, WHEN, WHERE.

How the strip is applied has more to do with convenience and availability than anything else but there are a few criteria I suggest be met. The strip should be at least 10 ft wide and 300 ft long. The rate should be 40 to 50 lbs N (above the rest of the field) for grain only wheat and canola, 80 lbs N for dual purpose wheat. The normal recommendation is that when applying pre-plant either have a second, higher rate programmed into the applicator or make a second pass over an area already fertilized. Many will choose to rent a pull type spreader with urea for a day, hitting each field.


Also popular are applicators made or adapted for this specific use. ATV sprayers are the most common as they can be multi-purpose. In most cases a 20-25 gallon tank with a 1 gpm pump is placed on the ATV with an 8-10ft breakover boom. The third applicator is a ride away sprayer with a boom running along the rear of the trailer. In all cases when liquid is the source I recommend some form of streamer nozzle.
If this all sounds like to much then the easiest application method might just be a push spreader. No need for trailer or even a truck. In most cases I recommend whichever N source is the easiest, cheapest, and most convenient to apply.

Vincent N-Rich Strip Applicator, Ponca City OK
Vincent N-Rich Strip Applicator, Ponca City OK
Gard N-Rich Strip Applicator, Fairview Ok
Gard N-Rich Strip Applicator, Fairview Ok
Push spreader used by Oklahoma State Cooperative Extension service. Check with your local office. If they don’t have one, we can send one.

When the strip is applied in winter crops proper timing is regionally dependent. For the Central Great Plains, ideally the fertilizer should be applied pre-plant or soon after.  However,  in most cases as long as the fertilizer is down by December or even January everything works. Timing is more about how much the wheat is growing. If it is slow growing fall, timing can be delayed. When the N-Rich Strip approach is used on the Eastern Shore in Virginia and Maryland the strips have to be applied at green up. We have been trying this in Oklahoma and Kansas with good success.  It is always important to make the tools fit your specific regional needs and practices and not the other way around.

Where is actually the biggest unknown.  The basic answer is to place the N-Rich Strip in the area that best represents the field.  Many people question this as it doesn’t account for spatial variability in the field, and they are correct.  But my response is that in this case spatial variability is not the goal, temporal variability is.  Keeping in mind the goal is to take a field which has been receiving a flat yield goal recommendation for the last 30+ years and make a better flat rate recommendation.  My typically request is that on a field with significant variability either apply a strip long enough to cross the zones or apply smaller strips in each significant area.  This allows for in-season decisions.  I have seen some make the choice to ignore the variability in the field, made evident by the strip, and apply one rate and others choose the address the variability by applying two or more rates.  One key to the placement of N-Rich Strips is record keeping.  Either via notes or GPS, record the location of every strip.  This allows for the strips to be easily located at non-response sites.  It is also recommended to move the strip each year to avoid overloading the area with N.  

For more information on N-Rich Strips

Factsheets

https://extension.okstate.edu/fact-sheets/applying-nitrogen-rich-strips.html

https://extension.okstate.edu/fact-sheets/using-the-greenseeker-handheld-sensor-and-sensor-based-nitrogen-rate-calculator.html

https://extension.okstate.edu/fact-sheets/impact-of-sensor-based-nitrogen-management-on-yield-and-soil-quality.html

Related Blogs

YouTube Videos  

Nitrogen Source: What’s “cheap” now may be lost later

Raedan Sharry, Ph.D. Student, Precision Nutrient Management
Brian Arnall, Extension Specialist, Precision Nutrient Management

Note, this blog is focused on grain only winter wheat production.

Crop producers looking to increase profits often consider how to reduce costs without sacrificing yield and/or quality. This applies to essentially all production functions including nitrogen application. Winter wheat growers in the southern Great Plains have a wide number of options available to them when considering nitrogen source and application technique. At the time of writing (08/27/2021) fertilizer prices obtained from the Two Rivers Farmers Cooperative are as follows ($/unit): UAN (28-0-0) $0.62, NH3 (82-0-0) $0.45, and Urea (46-0-0) $0.62. These price levels equate to approximately a 57% increase in urea cost, 65% increase in UAN28, and a 65% increase in NH

Application Timing

Winter wheat producers in the southern plains have historically applied nitrogen (N) fertilizer prior to planting, often utilizing anhydrous ammonia for application due to its generally lower price point per unit of N relative to other sources. However, research at Oklahoma State shows that if the total N application is delayed until approximately feekes 5 to feekes 7 stages (jointing) yields were increased 23% of the time while grain protein was increased 68% of the time. By delaying N application to later in the growing season N is more likely to be available when the crop requires by avoiding conditions conducive to losses. Further reading on delaying nitrogen application can be found here (https://osunpk.com/2020/09/10/value-of-in-season-application-for-grain-only-wheat-production/)

A study located a Perkins, OK observing yield and protein response provides an example of an expected response to delayed N. In this study 3 N fertilizer rates (180, 90 and 45/45 split) across 5 different timings (Pre, 30, 60, 90, and 120 days after planting) where investigated. Grain yield was maximized by the 180 lb. rate applied 60 days after planting, while protein was maximized at the 120 days after planting timing. This same trend continues across all N rate levels as the later N applications whether at 60 or 90 increased yield relative to the pre while the 120 days after planting application maximized protein level regardless of rate level. However, maturity of the 120 day application treatment was severely delayed. This experiment shows the ability to sustain yield while decreasing N rate if N application is pushed to later in the season to avoid conditions that lead to N losses as displayed by the 90 lbs. at 90 days after planting treatment compared to the 180 lb. pre-plant rate.

Winter Wheat grain yield (bushels per acre) and grain protein (%) results from a study looking at application of nitrogen. Zero, is zero N check, 180 and 90 treatments were all of the 180 or 90 lbs N per acre was applied at pre-plant, 30, 60, 60, or 120 GDD>0 after planting. The 45s refers to split application were 45 lbs N was applied at pre-plant and an additional 45 lbs N was applied at 30, 60, 60, or 120 GDD>0 after planting. All N applied at NH4NO3. Pre (4.11.20), 30 (8.12.20), 60 (2.23.21), 90 (3.19.21), 120 (5.2.21). Blue bars are grain yield, orange dots protein.

Application Cost

Application costs are directly related to choice of source utilized. For instance; anhydrous ammonia application is predicated on the use of a pulled implement such as a low disturbance applicator for in-season application or a tillage implement for pre-season application. This is compared to other sources such as urea or ammonium nitrate which may be broadcast, or UAN that can be applied using a sprayer. The relationship between source and cost of application is inherently related to the application efficiency of the equipment used. Table 2 below provides a rough idea of cost associated with different application methods. (Information Retrieved from Iowa State). Fuel cost assumed at $2.60/gal. Labor cost assumed to be $15.00/hr.

ImplementOperating EfficiencyFuel cost/acLabor Cost/acOperating cost/ac
90’ SP Sprayer~78 ac/hr$0.34$0.19$0.53
60’ Dry Spreader~30 ac/hr$0.39$0.50$0.89
35’ Sweep Plow~21 ac/hr$1.43$0.71$2.14

In many operations across the southern plains efficiency has become a key factor in decisions such as input selection and equipment purchases. This has come in response to the need to cover more acres with less labor. With that in mind and looking back to table 2 it is easy to see that a self-propelled sprayer is likely able to cover more acres than other equipment options. This most likely should be considered when considering options for N management in the wheat crop.

Summary

With wheat sowing quickly approaching for many and field preparation nearing completion it is important to consider your nitrogen management options. Delayed N application allows for flexibility in management plan and depending on source utilized may increase application efficiency over pre-plant applications requiring a tillage implement. As fertilizer prices continue to remain high it is also important to consider the likely increase in N use efficiency due to applying N closer to when N requirement is peaking. Controlling cost while continuing to maximize output is imperative to sustainable profitability in crop production.

Any Question or Comments please feel free to reach out me.
Brian Arnall b.arnall@okstate.edu

Soil Acidity and Cotton Production

Raedan Sharry, Precision Nutrient Management Ph.D. student
Brian Arnall, Precision Nutrient Management Extension Specialist

Cotton production in Oklahoma has expanded the past decade into areas which other production systems such as continuous wheat may have traditionally dominated. Fields that have been managed for continuous wheat production may have become acidic in response to management practices, such as the use of ammoniacal nitrogen fertilizers. In response to the acidification of these soils it may be important to recognize and understand the potential impacts of soil acidification on cotton production.

To better document the impact of soil pH on cotton lint yield and quality a study was conducted over the 2019 and 2020 growing seasons at two locations: Stillwater, OK (EFAW farm) and Perkins, OK. Soil pH in these experiments were adjusted to a depth of approximately 6 inches using aluminum sulfate (acidifying) and hydrated lime (alkalinizing). All three locations were planted to two varieties; NexGen 3930 and Deltapine 1612 at a rate of approximately 35,000 seeds per acre, into plots with soils ranging in pH from 4.0 to 8.0.

In season measurements taken included stand count, plant height, node count and NDVI (normalized difference vegetative index. All four in season measurements demonstrated a significant critical threshold in which soil pH negatively impacted crop performance. Stand was significantly decreased at a soil pH of 5.3 or lower. This trend is displayed in Figure 1. Plant height and node count depicted in figures 2 and 3 respectively were both significantly decreased when soil pH dropped below 5.3 and 4.9, while NDVI began to deteriorate around a pH of 5.1 (Figure 4).  Response to soil pH level was also visually observable as shown by Figure 5 from the Perkins 2019 location.

Figure 1. Average plant stand per 10ft of row when all three sites of a soil pH and cotton experiment were combined.
Figure 2. Relationship between soil pH and plant height across all 3 sites in a soil pH and cotton experiment. (Critical threshold: pH=5.3)
Figure 3. Relationship between soil pH and node count across all 3 sites in a soil pH and cotton experiment. (Critical threshold: pH=4.9)
Figure 4. Relationship between soil pH and NDVI across all 3 sites in a soil pH and cotton experiment. (Critical threshold: pH=5.1)
Figure 5. Side by side comparison of Deltapine 1612 and NextGen 3930 across a range of pH levels at the Perkins, OK 2019 site .

Yield levels across this experiment ranged from 0 to 1284 lbs. of lint per acre. In this work yield is reported as relative yield. To calculate relative yield the yield of each plot is normalized to the average of the three highest yields for that site. This method of reporting yield response allows this work to be applied across a range of yield environments.

Figure 6. Relationship between soil pH and relative yield across all 3 sites in a soil pH and cotton experiment. (Critical threshold: pH=5.4)

When all sites and cultivars were combined relative yield reached a plateau at approximately 73% of yield with a critical threshold observed at a pH of 5.4. Below this critical threshold yield decreased at a rate of 37% per point of pH decline. This equates to 15% yield loss at a pH of 5.0, 33% yield loss at a pH of 4.5, and 52% yield loss at a pH of 4.5. This relationship is depicted in Figure 6. It is important to note that yield was 0 when pH was 4.3 in two plots. This represents the possibility for total crop failure when planting into very acidic conditions.

Differences in relative yield between cultivars were insignificant. However, further investigation may produce a significant difference. Critical threshold for the DP 1612 and NG 3930 cultivars were 6.1 and 5.2 respectively. This suggests that there may be value in further examining the influence of genetics on cotton response to soil acidity.

Figure 7. Relationship between soil pH and relative yield across all 3 sites and separated by cultivar in a soil pH and cotton experiment. (Critical pH threshold: DP 1612=6.1, NG 3930=5.2)

SUMMARY

              The influence of soil pH level on cotton productivity is confirmed by this study. All three sites evaluated provided a strong correlation between soil pH and lint yield, as well as the in-season growth parameters measured. While this study is likely to be expanded to another location to provide a more robust evaluation of the potential impact of soil acidity on cotton, the current dataset provides ample evidence to conclude that soil acidity is likely to be detrimental to cotton production in the southern plains. Soil pH levels below 5.5 appear to provide the greatest opportunity for yield loss as depicted above. Lint quality measurements taken in the study (micronaire, length, uniformity, and strength) showed no consistent trends in the relationship between quality parameters and soil pH suggesting that soil acidity had a limited influence on lint quality characteristics. Cotton response to soil pH is likely to be influenced by the environment of a specific location and growing season. This underlines the importance of understanding the soil properties that negatively impact productivity, such as the presence of toxic forms of aluminum or manganese. It is also important to highlight the possibility of acidic conditions significantly affecting the ability of the crop to access important nutrients such as phosphorus. Under acidic conditions cotton productivity is likely to be significantly decreased unless soils are neutralized using a soil amendment such as lime.

Project Supported by the
Oklahoma Cotton Council
Cotton Incorporated
Oklahoma Fertilizer Checkoff Program