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I have been trying to write this blog addressing the yellow wheat for about two weeks now. But with finally finding a dry”ish” day or two and a lot of calls and emails about yellow wheat, I am just now getting to it.
So the short story is there is a lot of wheat out there in the state that is show signs of chlorosis, or yellowing. I wish I could say I have all the answers for you in this article, but I will have to lay heavily upon the agronomist best answer, “Well it Depends.”.
First we will start with the things I know least about and then move on to things that are more in my wheelhouse. In the last two weeks I have been on multiple email strings trying to chase down the cause of chlorosis in fields all over the state. One of these included Dr. Bob Hunger and the Plant Disease & Insect Diag Lab (PDIDL) and in one field his final thought was “So, my best guess is cold and wet soils along with fungi colonizing the older leaves that are starting to senesce.” At the same time I am finding regular occurrence of Tan Spot and Leaf Rust increase. All these pathogen cause some level of chlorosis and if you do not get down and pull some samples you will never know the cause.
A new for me this year is what I am calling the herbicide ding. I was able to get over a lot of my wheat that first week of March with a shot of herbicide, everything was almost to hollowstem. The wheat really got dinged. Very visual yellowing and stunting of the plants. Talking with Dr Manucheri, she had seen the same thing in her plots in Tipton. I have also visited several farmer fields with the same symptoms. Dr. Manucheri shared with me the Finesse label. Directly from the label “Temporary discolorations and/or crop injury may occur if herbicide is applied when the crop is stressed by severe weather conditions (such as heavy rainfall, prolonged cold weather, or wide fluctuations in day/night temps), disease or insect damage, low fertility, applications to course soils, or when applied in combination with surfactant and high rates of liquid fertilizer solutions.” This can be found on page 5, http://www.cdms.net/ldat/ldFSL002.pdf . You can just about mark off every weather and application condition mentions, on the same field.
Now to the yellow wheat I can comfortably talk about. There is nitrogen deficiencies out there. That should not come as a shock with the amount of rain we have received over the last couple months. I also believe that a fair amount of the wheat crop out there is a bit lacking on roots department.
The overarching wet cools soils that we have more than likely have led to reduced root exploration in some areas. And if you combine short roots with a nitrate leaching then the probability of N being out of the reach of the crop is high. Then the question is “Is there still time to do anything?”. The trip I look over the weekend (3/28, 3/29) that encompassed a great deal of the North Central Ok wheat belt showed me that the majority of the wheat had really progressed physiologically in the last two weeks. At this point, a positive return on N investment hinges on the stage the wheat is at.
Our delayed N work over the past several years show that we have maintained the yield on our trials even when fertilizer was delayed into the first week of April. https://osunpk.com/2019/08/14/how-long-can-wheat-wait-for-nitrogen-one-more-year-of-data/
This table shows the application dates of the 10 site years of the delayed nitrogen study. The first column is the location, to the right of the location is two rows the top is grain yield and the bottom is grain protein. Each of the following columns corresponds to an application date. Applications began at each study when the The colors are related to whether that application was statistically (Alpha=0.05) worse than, equal too, or better than applying nitrogen at the first sign of deficiency (0DAVD). For this comparison it is important to know that at no location did preplant have significantly greater yield than 0DAVD.In the majority of those years that first week of April corresponded with the growth stage Feekes 8, last leaf just visible. As the crop moves beyond that point, catching up did not happen. Currently there is wheat out there in the state that has not hit hollow stem (Feekes 6) and there is wheat at Flag leaf (Feekes 9).
The high rainfall totals we have could have also led to another deficiency sulfur. In the past S deficiency is fairly hard to find in Oklahoma. Our long history of low S using winter wheat and high sub-soil S levels have kept the response to Sulfur low, but not uncommon. Sulfur is a mobile nutrient and will also be lost via leaching especially in sandy soils in the northern part of the state. Sulfur deficient is different from N in that it shows in the newer growth as a general yellowing of crop. Kansas State has a lot of great resources on sulfur management in wheat. https://webapp.agron.ksu.edu/agr_social/m_eu_article.throck?article_id=2132
If your wheat is yellow and before you call the fertilizer applicator, first confirm it is nitrogen and or sulfur and not something else. A key point to nitrogen deficiency is that the cholorsis will be worst on the oldest leafs while new growth is green. If N deficiency is confirmed then figure out how far along your wheat is. If the crop is around hollow stem to Feekes 8, if you can get the N on soon there is a good chance to get your money back plus. Keep in mind with air temps above 60 degrees UAN will burn the tissue so it is best to use streamer nozzles, which will still burn but the tissue damage is lessened. If you do not have access to streamers you can dilute the UAN with water and use flat fan nozzles. Cutting the UAN with water reduce the impact of leaf burn, I typically recommend at least 2 part UAN to 1 part water, but a 1 to 1 is the safest.
If you have any questions or concerns please feel free to email any questions you may have.
In the spring of 2014 we initiated what was to be the first year of a three year project evaluating starter fertilizers for soybean production in the southern Great Plains. The first and second year was and is being funded by the Oklahoma Soybean Board.
Year one was a bit experimental in that with so many products on the market we needed some initial work to help focus the direction for years two and three. I also added a treatment which I knew would have significant negative impact, for extension reasons. Keep in mind two locations in a single year does not make an experiment nor provide enough information to draw a definite conclusion. It is however enough to learn some lessons from and for us to plan for our 2015 trials.
The 2014 trial consisted of 12 treatments, Figure 1 and Figure 2. In these treatments I wanted to see the impact of a standard practice, see if a specific nutrient may be more so beneficial, and evaluate a few popular products. The spring of 2014 started out dry so at one of our two locations we pre-watered. This was done by hauling water to the Lake Carl Blackwell (LCB) 1000 gallons at a time and pumping through sprinklers. The other site, Perkins, we delayed planting until we had moisture.
The two locations were also selected due to differences in soil fertility. The LCB site is has good soil fertility, with exception of phosphorus (P), and the Perkins site pH was an issue. I would have expected a benefit from adding P at both of these locations. Figure 4 shows the soil test results.
At LCB as expected some of the treatments (Thio-Sul) reduced stand, some unexpectedly reduced stand (Fe) and others had less impact on stand (APP 5.0) than expected. The growth at LCB was tremendous, the 30 in rows covered over very quickly and the majority of the treatments hit me waist high by early August (I am 6’0”). Many of the treatments showed greater growth than check. But when it comes down to it, grain pays and green does not. Statistically there were no treatments that out preformed the un-treated check, however the K-Leaf and 9-18-9 did make 3 and 2 bpa more than the check respectively. What I am hypothesizing at this site is that the added nutrients, especially those with high P levels, significantly increased vegetative grown and these big plants were delayed into going reproductive and they started setting pods later in much hotter weather. While riding in the combine I could see that the plots with compact plants with clearly defined rows out yielded those were the vines had crossed over and we harvested through more of a solid mat of mature plants. A hot August is not uncommon and I am curious on whether this trend repeats itself. If it does this may direct us into research evaluating ways to force/promote the reproductive stage to start in these big plants. Even if we can force flowering to start earlier, it’s unknown whether yields will increase or not.
The same trends in treatments reducing stand can be seen at Perkins, however the impact was less extreme. Perkins being planted later due to waiting on moisture forced a later flowering date and I believe reduced overall yields. But the addition of P at this low pH site definitely made a difference. While again no treatments were statistically greater than the un-treated check the 2.5 gpa APP, DAP broadcast, APP/H2O, and Pro-Germ/H20 treatments increased yield by 5.6, 4.2, 3.8 and 1.7 bpa respectively.
Take home from year one was that at LCB the addition of a starter fertilizer had little benefit and if done wrong could cost you yield while at the low pH site of Perkins an addition 2.5 gallons of APP did get a 5 bpa bump, but do to variability in the trial the increase was not statistically significant. This year we will drop some of the treatments and incorporate a few new treatments. Based on the current weather we look to potentially being able to start with better soil moisture at planting. Again do not take this work and significantly adjust any plans you have for your 2015 soybean crop. This is however some interesting findings that I wanted to share and make everyone aware of. Finally thank you to the Oklahoma Soybean Board for providing funding for this work. www.oksoy.org/
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. Due to our fertilizer applicators this is typically a strip. The approach maybe somewhat 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. I like to tell producers that the goal of the N-Rich strip is to make a really big cow pie.
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.
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 no less than 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.
Becoming more popular are applicators made or adapted for 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. In most cases there is not a great deal of thought put into what source. I recommend whichever source is the easiest, cheapest, and most convenient to apply.
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 the first of November everything works. This does not say a strip applied after this time doesn’t work but it leaves more room for error. There is a chance the crop could already be stressed or the nitrogen tied up and not release in time. However 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. The soils in that region are very deep sands and nitrogen applied in the fall may not make it to the spring. Also most wheat producers in the area make three or more applications of nitrogen unlike the two (pre and top) of the Great Plains. 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 spacial 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.
I hear a great deal of talk about how it would take to much time to put out the N-Rich Strip. However the majority of producers that do it once on one field, end up doing it every year on every field. There is very likely someone in your area who is using the N-Rich Strips. As top-dress grows closer keep an eye out for a blog “Using the GreenSeeker Sensor and Sensor Based Nitrogen Rate Calculator”.
For more information on N-Rich Strips check out the YouTube video below, visit http://www.npk.okstate.edu or contact me directly at firstname.lastname@example.org. I have lots of material I am happy to share and distribute.
See the YouTube Video http://www.youtube.com/watch?v=kJ3DSwWYgE8