Joao Bigatao Souza, PhD. Student Precision Nutrient Management
Brain Arnall Precision Nutrient Management Extension Specialist.
The N-rich strip method allows wheat producers a greater window of decision making regarding the application of nitrogen (N) fertilizers. Besides having greater accuracy in N rates than standard methods (based on the SBNRC – OSU) also helps to reduce costs in the production system and to preserve the environment avoiding over N applications.
With the experiments performed in the last two crop seasons (2016/18 and 2017/18), we can now be even more accurate with regard to the best application time to increase the N use efficiency by the crop. The objective of our study was to determine the impact of prolonged nitrogen deficiency on winter wheat grain yield and protein. Eight studies were conducted with 11 N application timings in no-till dryland conditions. A pre-plant treatment of 90 lbs ac-1 of N was broadcast applied as ammonium nitrate (AN). We used AN as our source because we wanted to measure the crops ability to recover and eliminate the impact of source efficiencies. When visual symptom differentiation (VSD) was documented between the pre-plant and the non-fertilized check, i.e the N-Rich Strip showed up, top-dress applications were performed every seven growth days (GDD> 0) (https://www.mesonet.org/index.php) until 63 growth days after VSD at all sites. The only N the treatments received where applied according to treatment structure. No preplant N was applied other than trt 1, and all locations had residual N under 15 lbs 0-6” sample.
The first visual response to fertilizer N ranged from November 11 to February 5 (Table 1). The soil can have residual N from the previous season which can supply the subsequent crop in the beginning of the development what makes the wheat not demonstrate any sign of stress in the early season. For example LCB2017 a and b which were located 100 yards apart but under a different point in the crop rotation (LCBa was wheat after wheat and LCBb wheat after canola) had a 30 day difference in date of first N response. This range in first and last dates allowed us to evaluate N application over a wide range of dates and determine whether the first sign of stress is actually the best indicator of top dress application timing.
As shown in the Tables 2 and 3 below only three of the 78 comparisons made back to the pre-plant application were significantly less in terms of grain yield. All three of these comparisons where from when N application was delayed until late March or April. When the delayed applications were compared to 0DAVD yields only two of the 68 comparisons showed a significant decrease on yield. One was the pre-plant application for LCB2017a while the other were the 63DAVD application for LCB2017b. In most locations applications made in March yields were at the highest point, however when delayed till April yield trends on the downward trend. The 2017 crop reached hollow stem (Feekes 6) around Feb 20th while the 2018 crop reached hollow stem around March 10th.
Grain protein concentration was decreased only once when compared to both the pre-plant and 0DAVD treatments. This one timing, LCB2018b 64DAVD, was the only application made in May. During this time the crop was in the early stages of grain-fill. In all locations delaying N application until February/March increased grain protein content above the check, and in most cases above the 0DAVD trt.
All the data was combined and plotted by cumulative GDD’s>0 from planting (GDDFP) across all locations to determine a general “best” timing. Using the pre-plant application yield as a base there was no yield loss if the applications was made prior to the 143 GDDFP. When the results were normalized by 0DAVD N there was no yield loss if the applications were made prior to 130 GDDFP. The quadratic model created provides the opportunity to identify the point of highest grain yield, which was approximately 94 GDDFP. In terms of the relationship between the application of N based on GDDFP and % of protein content on the grain, a linear response of N delay application observed for grain protein concentration. Our results suggest that the later the application, the higher the protein % in the grains.
We have concurrent work looking at similar approaches with other sources of N such as Urea and UAN. While all of these studies are being continued the past two years of work have presented some easy take homes.
First: Timing of N application does matter, but yellow wheat does not necessarily mean yield loss.
Second: Two years in a row ALL Nitrogen could be delayed until hollow stem without yield Loss, in fact yields of trts with N applied at this time typically better than that of the pre-plant.
Third: Protein content increased as N applications was delayed.
Fourth: The conclusions of this and other studies support that N-Rich Strip concept does not increase risk of lost yield.
Fifth: Applying the majority of the N at or just after hollow stem maximized grain yield and protein with a single shot.
Sixth and Final: Be more concerned about applying N in an environment conducive to increased utilization and less about applying at the first sign of N stress. Take a look at the wheat N uptake curve by K-State.The crop really doesnt get going in terms of N-uptake until jointing i.e. hollow Stem.
Questions for comments fill free to contact me via email at email@example.com
Misha Manuchehri and Brian Arnall
There are many factors that influence the persistence and uptake of a herbicide that has soil activity. One of those factors is soil pH or the amount of hydrogen (H) ions present in the soil solution. Some herbicides will persist for an extended amount of time or rapidly degrade when outside the pH window of 6.0-7.0.
The triazines (atrazine, simazine, etc.) and sulfonylureas (chlorsulfuron, metsulfuron, etc.) are two herbicide chemical families that are especially affected by soil pH (Table 1). The dinitroanilines, and the active ingredient clomazone also can be affected by low and high soil pH; however, degradation by light and/or volatility are more important when it comes to the activity of these herbicides. Generally, the triazines and sulfonylureas persist longer and are more available for plant uptake in higher pH soils (>7.0) while the opposite is true for imidazolinone herbicides (imazamox, imazapic, imazethapyr, etc.). Imidazolinones persist and are more available for plant uptake in lower pH soils (<6.0). The persistence of the triazines and sulfonylureas in high pH soils is a result of a decrease in chemical and microbial breakdown, a trend that is often observed in high pH soils where neutral herbicide molecules are loosely adsorbed to the soil and are more available for plant uptake. Conversely, in low pH soils, triazine and sulfonylurea herbicides become charged and are more tightly adsorbed to the soil where they are more susceptible to breakdown.
A key management factor that must be considered when evaluating a field’s soil pH is whether or not the field is no-till and for how long it has been in no-till. Tillage will impact how deep you should take soil samples to determine soil pH. In no-till and minimum tillage fields, the traditional method of 0-6 inch or 0-8 inch soil cores may not be adequate. Instead, a 0-2 inch core depth and a 2-6 inch core depth may be needed, since application of limestone to the surface may increase surface pH more than expected or application of nitrogen fertilizer to the surface may cause a drop in pH at the surface. In many long term no-till fields with historic surface applications of N and no lime applications, soil pHs in the low 4s have been observed while the 3-6” depth will be at a 6.0. Since herbicides with a soil residual are affecting plants just below the soil surface, this is the soil zone we are the most interested in.
Oklahoma and Kansas production fields can have a wide range of soil pH from field to field and within field. In a dataset of over 300 grid sampled fields from Oklahoma (259 fields) and Kansas (47 fields), the average field pH was a nice 6.0. However, the average range in the lowest and highest soil pH within the fields was 1.9. This means the average field had a pH range from 5.0 to 7.0. It should be noted that more than 25% of the fields had a pH range of 3.0 units. This range of highs and lows has helped explain the presence of spotty herbicide issues on several fields in the past and should be taken into account when planning crop rotations.
It is extremely important to know and understand the pH of your soils and the herbicides you plan to use and how they will react. Soil testing is the only way to know your soil pH and reading your herbicide label is a great way to learn if soil pH affects the herbicide you are applying.
Table 1. Herbicide chemical families or selected herbicides that are most affected by soil pH.
Herbicide chemical family or active ingredient
Common name (trade name) examples
Importance of soil pH
Soil pH considerations
Chlorsolfuron + metsulfuron (Finesse C & F), metsulfuron (Ally XP)
pH > 7a – persist longer and are more available for plant uptake
|Atrazine (AAtrex), simazine (prince)||
pH > 7 – persist longer and are more available for plant uptake
Imazamox (Beyond), imazapic (Plateau), imazethapyr (Pursuit)
pH < 6 – persist longer and are more available for plant uptake
aAcidic Soils < 5.5, Basic Soils > 7.5
As I write this it does not seem possible that my first Ag App Blog was written over five years ago. https://osunpk.com/2013/07/30/agriculture-app-for-the-ipad-and-iphone/. When I wrote that first blog I had 76 apps on my iPad a year later I had over 200 apps on the same iPad posted the third app focused blog https://osunpk.com/2014/12/09/agriculture-apps-200-strong-and-growing/.
Today I still enjoy looking for apps and I am also having a lot of fun developing apps. With a team of computer science students we have released twenty eight apps in both iOS and Andriod platforms http://www.dasnr.okstate.edu/apps. After I had picked up a few new apps, broke the 300+ mark, I found that my five year old iPad 2 was not quite as quick as it used to be and I had to upgrade prior to doing my Scouting App Review https://osunpk.com/2017/08/03/scouting-app-review/.
Even after 300+ apps I still have a few of the same original suggestions, like the general rule of thumb “If I cannot figure it out in 3 minutes it’s GONE. An app should be intuitive, easy to use and have a purpose. They only exception to the 3 minute rule is the Scouting and Mapping Apps. Because of their complexity I allow them 5 minutes, and then I am done. Any app with GIS in its name gets much more time”. As far as searching for apps terms such as Corn, Soybean, and Wheat return more games and dietary apps than useful ag apps. Multiple key work searchers is important. If you find a good app go into iTunes or Google Play and check out the other apps created by the developer. Chances are if the developer has made one app you like there will be other well suited to your needs.
But to be honest as you can expect of those 300+ apps 95% only get opened when I have to give a talk. Recently I have had request to update my list of apps but instead of spending the countless hours organizing my thoughts on the 300+, I decided on just sharing with you those apps which have made their way onto my cell phone because I do use them. Many of these are on my original blog 5 years ago.
Tank Mix is a handy app that allows the user to create chemical inventories, plan spray jobs, share the details and save for later. Minus wading through the list of chemical this is a very intuitive app and provides a great deal of information. The ability to create a library of chemical and application really streamlines the systems.
SPRAY SELECT Apple
Spray Select was the first app I downloaded. While over the years it has had its fair share of bugs, in my line of work this app is a gem. In a day I may go from spray a contact, to a fertilizer, to a systemic. Not to mention the wide range of GPAs I run at. Being able to to select my speed and GPA then have a list of tips and droplet sizes makes this app critical for my project. I primarily use TeeJet but if you use Hypro check out AgPhDs SprayTipGuide, if you use Greenleaf download NozzleCalc, JohnDeere has an app for their nozzles also.
I have two Nutrient Removal Calculators on my iPhone the Fert Removal from AgPhD and Nutrient Removal from IPNI. I give Fert Removal the leg up because it provides nutrient values for more than just the macro nutrients.
The AgPhDs put out another nice app in Deficiencies. Nice funcitonality but image library is a bit limited. It is my hopes that they are adding to this over time. Much like with the nutrient removal tools I give second runner up in this group to the IPNI PlantImages app. It has a larger image data base but at the time of this blog it needs updating and is not functioning on all platforms. Both apps are on my phone and are great tools for someone new in the field, or someone who has been around a while but who’s client needs to a see a second opinion.
I like the easy of use for of the Corn Yield Calculator. It is a quick, easy, and clean way to estimate yield. However when I pulled the links for this app it seems as though since I first downloaded the app, a fee has been added, $2.99. For some of you it may be worth the charge. However University of Wisconsin has a nice app named Crop Calculators. It has several functions but the UI (user interface) is not as clean.
Another app by the Ag PhDs is on my list. For me the Harvest Loss App is what I use as an example for the perfect “app”. Harvest loss allows the user to choose the commodity and current price. Then the number of grains found in a square foot after harvest is counted. This provides an economic value to properly setting a combine. What more powerful tool than money lost is there to impact change.
These are not the only Weed Identification apps, but they are my favorite. University of Missouri’s IDWeeds was the first of its kind and has made some fantastic improvements over the years. Monsanto’s WeedID app is, IMHO, one of the cleanest and nicest user interfaces available. Both function similarly, the user selects grass or broadleaf, then chooses the appropriate physiological features of the weed in question. A list of weeds fitting the description is compiled. Pictures and more in-depth descriptions are available.
While this app is built for the UK, being in the southern Great Plains wheat is king and this is a very useful app when it comes to cereal disease. While it does not have a good ID tool it has a great list of diseases, images and very in-depth descriptions.
This app just makes me smile. But it really does have some great features and could be quite useful or any cattle producer. By considering the consistency of the pile the quality of the forage/feed can be estimated.
Of course I have all of the OSUNPK apps on my phone but here are a few that I think were homeruns. The full list can be found at http://www.dasnr.okstate.edu/apps
While Canopeo is not mine its the best thing since sliced bread. This app uses the camera on your phone or tablet to get a % canopy cover. The Android version even has a video version. The applications for this app are endless.
OKSTATE SOIL SAMPLE
Designed for individuals who send samples to the OSU Soil, Water, and Forage Testing Labs (SWFAL). User can collect the GPS location of a sample, add notes, and tie it to your lab ID and sample number via a barcode. I know some who just use this app to get Lat Longs from sample points. At this point the app is not tied to the Lab system. But a file can be emailed with all of the saved data.
Simple calculator that will calculate annual nutrient additions when you have a irrigation water test.
Handy app built to help calibrate grain drills to sow canola with the added function of determining rates of other grains and fertilizers.
Non Ag but extremely popular app designed for a DIY food plot. Pick your species of interest and planting window and a list of applicable plants and their agronomic recommendations are provided. Lists can be saved and shared.
Built to help graduate students prep fertilizer for plot application. The app also has a unit conversation calculator.
If you are free in the middle of July, make your way to InfoAg in St Louis (July 17-19, 2018). I will be going through these app and many more in a app review and demonstration. For more info on InfoAg check out their website. https://infoag.org/
Questions for comments fill free to contact me via email at firstname.lastname@example.org
During January and February I spent a lot of time on the road giving precision ag and wheat yield / protein talks. One thing about giving the same talk multiple times and spending countless hours on the road, about 70, is the time you have to think about the little things in your talk. This time around it was the slide below. The graph is from the 502 Long Term Fertility study located in Lahoma OK. When I first put the slide together in 2016 the purpose was to show how the yield and optimum fertilizer rate is extremely varied. I went in to the 55 plus years of yield data and pulled out the past ten years and identified the nitrogen treatment, only those with full P and K fertility, that economically maximized yield each year. With the graph I was able to show how the nitrogen rate required to maximize yield changes dramatically each year and where the amount of N was not directly correlated with yield. But after showing this graph a few times I thought that added lbs of N per bushel would help me highlight the point about changing N demand. That’s the blue numbers below each year. And of course out of curiosity I averaged the numbers. The ten year average was 1.5 lbs of N, which would suggest over a ten year period you would need to apply 120% of the N removed to optimize profit.
The 1.5 lbs per bushel over time was an important number. Not long before I had reached out to half of dozen producers that I have spent at least 5 years with working on their N management. My question to them, what was your average yield and average N rate over all your fields and years. Turns out that most of these producers who were using N-Rich strips and making 2 or 3 trips over the field were averaging 1.5-1.6 lbs N per bushel of wheat produced across a farm. Of course when they told me this I was excited, that’s such an improvement over 2.0 lbs of N per bushel.
The real thought came with me combining these two independent tid bits. Can we provide a Nitrogen Management Report Card if we look at several years of yield history? Let me preface what is presented below is not a scientifically tested or proved concept, yet. The more I think about it the more I am beginning to think that YES we can do a beneficial postmortem analysis. This is not a 1 year analysis, in fact based on the long term data I have been looking at there needs to be 5 years of data per field evaluated. I also strongly contend that this is a by field process. This will provide the opportunity to look at management over a broad spectrum of soil types and weather.
The calculation for lbs of N per bushel is not tough. In a continuous grain only winter wheat system you would add up the amount of nitrogen applied per acre over the period you are evaluating. Sum up the annual average grain yield and multiple that value by 1.3. Divide the total N applied by the total N removed per acre. This will be a decimal value, to compare with the tables below multiple by 100 to get a percent. Based on the long-term trials there needs to be at minimum five years of data. But the more the better.
I would like to reiterate the grades provided below were not developed from any given data set. The report comments are of my own opinion. I do hope in the near future to utilize the Oklahoma State University long-term fertility studies to refine these tables.
For a field with a crop rotation the way to calculate is the same you will just need to go into each harvest and multiple yield by the N in the crop, then sum up those values.
For a field with a crop rotation with legume (or cover crop), I have adjusted the grade scale with the assumption less total N will be needed due to the addition of N fixed by the legumes.
Hopefully with concept will give you a different way to evaluate your N management strategies. This will not and cannot tell you what you need to apply next year. I mean just look at the data from Lahoma, from 2011 to 2015 optimum N rate ranged from 0 to 100 lbs N pre acre and N per bushel grown ranged from 0 to 2.2. Also as you look at the charts, understand that if you follow the old rule of thumbs 2.0 lbs N per bushel winter wheat and 1.2 lbs N per bushel for corn and sorghum, you are likely in the RED. These values are not that wrong for yield goal, 100% preplant application nitrogen management strategy. It is just with today technology, equipment, and agronomic practices we can do a lot better.
My final recommendations/comments would be:
1) If you are in the greens and yellows you are overall doing well. However there is always room for improvement. Are you currently accounting for the temporal variability in N demand, how about the spatial variability?
2) If you are in the orange and reds on the low side, are you there because you are underestimating yield or you are applying less because of grain prices?
There is likely money to be made by increasing yields with a little more nitrogen in these fields.
3) If you are in the orange and reds on the high side, are you there because you are consistently overestimating yield? Perhaps your yield estimation is not off but your lbs of N per bushel value is too high? Are you applying all of your N pre-plant. This practice is the most inefficient way, in terms of N use efficiency, to fertilize.
Questions or comments?
Please feel free to reach out to me via email or phone.