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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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Can Grain Sorghum Wait on Nitrogen?

Michaela Smith, Masters student under advisement of B. Arnall
Brian Arnall, Precision Nutrient Management Specialist

            Grain sorghum producers in Oklahoma are challenged greatly by their environment and sporadic rainfall patterns, which diminish as the season progresses. These uncontrollable variables influence timing of nitrogen (N) application and nitrogen use efficiency. Using rainfall events as an incorporation method forces producers to apply before the event regardless of its intensity or delay application until field conditions are acceptable while anxiously waiting for another rainfall event. When deciding to delay N application it’s important to know the effects on physiological development and grain yield.

Figure 1. Field trial at Perkins, showing visual heading differences among nitrogen application timings. Timing from left to right were made 49 DAP, CHECK, 63 DAP.

Trial structure and breakdown

            This study was conducted over the 2020 growing season consisting four locations, including one double cropping system following wheat. Ten in-season applications were made using ammonium nitrate (AN) as the N source at a rate of 90 lbs. ac. Using AN as the N source reduced the risk of nitrogen loss through the process of volatilization as the goal of the research was to test the plant not the fertilizer. A pre-plant treatment served as the standard check, while in-season applications were initiated at 21 Days After Planting (DAP) and applications made sequentially at 7-day intervals. A non-fertilized check was included to the study to confirm locations were responsive to N fertilized applications Hybrid, plant date, and seeding rate can be found in Table 1.

Table 1. Planting information or the delayed nitrogen sorghum trials.

Physiological Response to Application Timing

            Two of the four locations demonstrated an effect to physiological development and maturity with the delay of nitrogen application. A delay in heading by a one to two-week period was observed at Perkins and Lahoma for applications made after May 21st (Table 2.). This delay in heading contributed to similar delay in maturity and potential harvest date. At Perkins decreased plant height was observed in the pre-plant plot and was associated with the onset of late season nitrogen deficiency (Figure 2). While this response was unexpected, the impact of nitrogen deficiency experienced early in the crop growth on the root and shoot growth has been well documented in many species. As a plant experiences nitrogen limitations growth changes from above ground to the below ground parts (roots) in an attempt to alleviate nitrogen stress. This increase in root growth could contribute to a more efficient uptake of nitrogen and decrease loss. In contrast to Figure 2, pre-plant application is shorter than compared to later season applications, this could be a result of inadequate N uptake thus leading to N loss by leaching, whereas later applications had increased root growth for efficient N interception and uptake.

Table 2. Delay in Heading for the Perkins (gray) and Lahoma (green). Letters indicate the start and finish of heading. S represent the start of heading while F indicants the finish of heading, SF denote treatments the started heading and finished within the same week.
Figure 2. Visual maturity differences between nitrogen application timings. Timing of applications are listed within the figure.

Yield Response to Application Timing

Response of N was observed at all locations (Figure 3), while the delay of nitrogen varied in its effects across all locations. Grain yield from each N application was compared back to the pre-plant application to evaluate the effects of timing. All four locations responded positively to N fertilizer.  At both LCB and Lahoma grain yield was maintained with applications made as late as 42 to 63 DAP respectively before any negative trend in grain yield was observed. Perkins was the only locations to have a statistically significant increase in grain yield due to delayed N applications. At this site, which is a sandy loam, waiting until 42 DAP resulted in a 15 bushel increase over the pre-plant plot. Now Alva which was double crop showed that rainfall is key.  At this site, none of the in-season treatments made it up the level of the pre-plant. The reason for this will be discussed further below.

Figure 3. Grain sorghum yield results from the nitrogen timing studies conducted at four locations in Oklahoma.

Influence of Rainfall

            The loss in grain yield at Perkins in the pre-plant application could likely be reflective of nitrogen loss due to leaching. Pre-plant applications have been well documented in the aspect loss as a result of crop requirement and early physiological development. Long term mesonet rainfall data depicts a decline in the probability of rainfall with the progression of the growing season across all locations. In early season the probability of 0.5 inches of rainfall ranges from 8 to 10% respectively for LCB, Lahoma, and Perkins, and dramatically decline to percentages at low as 5% in mid-July during grain filling period. For Alva rainfall probability is substantially lower as its season was initiated during the drier months, which depicted a probability of 6% for 0.5 inches of rainfall, and 4.5% for 1 inch for early season rainfall crucial for pre-plant incorporation and crop establishment. These probabilities drop considerably compared to regular season as the months progress onward, mid to late August probability for 0.5 inches ranges from 0.8 to 11.5%, while for a 1 inch is 0 to 6.9%. Past weather data provided by the mesonet illustrates how later in the season rainfall and its amount is variable, suggesting that in a double crop scenario delayed application is not recommended while it is in regular season crop due to the increased chance of rainfall probability. 

Summary

            The purpose of this study was to evaluate the impacts of delayed nitrogen application in grain sorghum. In order to develop an accurate conclusion additional site years are required, although current data could suggest delaying nitrogen application for full season grain sorghum is possible without a detrimental loss in grain yield. This means producers have time to evaluate the crop and market to determine if more inputs are needed and economical, while allowing implementation of technologies such as the N-Rich Strip and SBNRC.

If you have any questions for comments please reach out.
Brian Arnall
b.arnall@okstate.edu
405.744.1722

Acknowledgement of LSB Industries for support of this project.

4 Keys to Reaching Grain Sorghums Yield Potential

When I started writing this blog (3.13.2105) Ok grain elevator cash bids for grain sorghum aka milo was 6.61-7.70 cwt (3.7-4.31 per bushel) and corn was at 3.64-4.06 per bushel. Meaning there is currently a premium on sorghum grain.  This difference among other things has increased the interest in planting sorghum.  Of late I have been quite successful, at least on a small-scale, at producing sorghum yield in the 120-150 bpa range, thanks to the advice of Rick Kochenower former OSU sorghum specialist.  Both of us believe that every year many producers are leaving significant bushels on the table due to one or two miss steps.  I wanted to take this opportunity to share what is in my opinion the keys in producing a bumper sorghum crop.  I should note that the primary key is out of our control, rain.

Key 1.  Planting date, the optimum planting date for grain sorghum is generally when soil temperatures reach 60° F and increase after planting.  For much of the region that I believe is best suited for sorghum this falls between April 1 and April 15 for south of I40 and April 15 and May 1 north of I40.  graph below shows the long-term average daily 4″ soil temp (bare soil) for Apache, Blackwell, Cherokee, and Vinita.  It is easy to see how your location within the state can impact soil temps.

Long term average 4 inch soil temps from Blackwell, Apache, Cherokee, and Vinita for bare soil.  Data from the Mesonet.org.

Long term average 4 inch soil temps from Blackwell, Apache, Cherokee, and Vinita for bare soil. Data from the Mesonet.org.

You should not forget however that tillage practices will also impact soil temps. The two graphs below show the  long-term average daily 4″ soil temp for Cherokee and Blackwell for both bare soil and under sod.  Note that when the soil is covered by residue it warms slower. The two figures also show that residue will have more impact in some areas more so than others.

Long term average  4 inch soil temps at Cherokee for bare soil and under sod.  Data from the Mesonet.org.

Long term average 4 inch soil temps at Cherokee for bare soil and under sod. Data from the Mesonet.org.

Long term average 4 inch soil temps at Blackwell for bare soil and under sod.  Data from the Mesonet.org.

Long term average 4 inch soil temps at Blackwell for bare soil and under sod. Data from the Mesonet.org.

My best word of advise is to keep a watchful eye on the Mesonet. While the long-term average is nice to know here in Oklahoma the difference in weather from one year to the next can be huge.  The figure below shows the  average daily 4″ soil temp (below sod) from Blackwell for the past five years.  Link to Mesonet Soil Temp page  Click here.

Average  4 inch soil temps at Blackwell for 2010, 2011, 2012, 2013, and 2014 for under sod.  Data from the Mesonet.org.

Average 4 inch soil temps at Blackwell for 2010, 2011, 2012, 2013, and 2014 for under sod. Data from the Mesonet.org.

Another great resource is a report on planting date written by Rick Kochenower presented to RMA. Link to report.

 

Key 2. Hybrid selection, primarily maturity group selection. Rick has created a great graphic that helps put a planting date window with maturity group.  It is always important to visit with your local seed dealer to find out what has been performing best in your region and consider the importance of stay-green, standablilty and disease packages. But for me the number one key is the selection of maturity group. This should be based upon planting date and harvest strategies. Below is a great graphic created by Rick, while this may not be scientific it is a great guide created via years of experience.  I also recommend that if you are planting a significant amount of acres you should diversify your maturity groups. Not only does this spread out he harvest window but it also you to spread the risk of high temps coming early or late.  An additional resource is the Sorghum Performance trial summary located on the Ok Panhandle Research and Extension Center website.  Click here.

Timeline for optimum planting date (N of I-40) and proper maturity groups.  Developed my Rick Kochenower (Chromatin seed)

Timeline for optimum planting date (N of I-40) and proper maturity groups. Developed by Rick Kochenower (Chromatin seed)

Key 3. Soil Fertility, while soil pH plays a big role on sorghum productivity but it is too late in the game to do much about it this year. So the most important things to keep in mind on fertilizing sorghum are your macro-nutrients nitrogen (N), phosphorous (P) and potassium (K).   It is my opinion that historically producers have underestimated the yield potential of sorghum and therefore lost yield due to under application on N. You should expect more than 60 to 80 bushel out of your crop if you put the right seed in the ground, at the right time and in the right way.
Ask around look at Rick’s yield data, producers in N. Central Ok on a good soil should be going for 125+ bpa easy. Unfortunately you are unlikely to hit these yield levels if you fertilize for a 75 bpa crop. An easy rule of thumb on N fertilization is 1.2 lbs of N per bushel, for a more exact number take a look at the image below.  This comes from the corn and sorghum PeteSheet and is the same table that comes from the Soil Fertility Handbook. (If you would like some Pete Sheets just send me an email requesting them at b.arnall@okstate.edu, Link to PeteSheets page).

Nitrogen, Phosphorus and Potassium Recommendations for corn and sorghum production.  Adapted from the Field guide and PeteSheet available at www.npk.okstate.edu

Nitrogen, Phosphorus and Potassium Recommendations for corn and sorghum production. Adapted from the Field guide and PeteSheet available at http://www.npk.okstate.edu

Key 4. Weed Control With sorghum utilizing a pre-plant herbicide with residual is extremely important due to the lack of over the top options.  Most times proper weed control will be accomplished by utilizing concept treated seed and use of labeled rates of a pre-emergent grass control herbicide combined with atrazine.

While I primarily focus of the four keys above there are a few other important items to consider.

Population: Prefer to think in terms of seeds per acre instead of lbs per acre.  This comes into to play with the use of a planter.  Rick Kochenower says “for seeding rate(on 30 inch rows), it isn’t  as critical as most people think it is.  Because most guys in Oklahoma tend  to under plant not over  plant.  I always suggested 45,000 but as you look at the last slide it really don’t matter much.  The way I always liked putting it is to make you sure have enough out there to not have to replant, because being late hurts more than having to few too many or too few plants.”

Row spacing:  I like 30, but many may not have a planter so I suggest at least plugging every other hole in the drill to be at a 12″-20″ spacing. Make sure your population is correct for your row spacing.  For this consult with your local seed dealer to match cultivar with row spacing and proper population.

Insects: Scouting for aphids and head midge is very important, these little critters are yield robbers and can gum up the works at harvest.

Harvest prep:  I almost put this as the fifth key.  By chemically maturing/terminating  your crop you are both able to increase harvest efficiency and preserve moisture for a following winter crop of wheat or canola.

While this is a good start I suggest a visit with your local OSU Extension educator, consultant or seed dealer for information about your specific situation.  Just know the crop has great potential to yield big if treated right.  I like to say don’t treat your sorghum crop like the stray you adopted, treat it like your hunting dog that you traveled halfway across the country to pick up.  Good luck in 2015 and I hope the rains fall when and were needed.