As I sit in my office writing this I am seeing the chances for Stillwater to get a good rain today slowly dwindle away. Last night we had a 75% chance of 0.56. Its now 3pm we have received 0.01 and have a 60% chance of getting an additional 0.10. And as this is how 2023 has gone, but we are still better off than so many west and north of us.

No some of the zeroed out wheat ground and winter fallow ground has seen its first moisture in 100+ days. Planters and drilling are rolling and or ready to roll. So I wanted to throw out a few thoughts and re-share an older blog.

In August of last year I was talking about how the extended drought was impacting organic matter and nitrogen cycling “Nitrogen cycle hiccups and a lot of drying“. Wish I could say things have changed since then but we all now otherwise. While we have moisture to plant and germ our H₂O fuel tank is far from full. Its going to take significant rainfall to rebuild the soil profile, not to mention the ponds. And I can not forget how last year we had great rains in May and were going pineapple by the end of July. I had N response studies all over the state in sorghum, at every trial nitrogen was not a limiting factor.

By this point if you know me or have every read anything I have written in the past you should know what is coming. My recommendation for pre-plant N is 0.0 lbs. Go ahead and put a starter down where you have low P or pH that’s out of range, and Fe and/or Zn in the calcareous soils where needed, but that’s it. We are continually adding to the research data base that says sorghum responds exceptionally well to in-season nitrogen applications in some cases nearly all the way to boot stage. I believe we are close to determining/explaining why the crop does so well but not ready to share that work just yet.

I just do not have the trust in the what rains may come to spend money on a fertilization pass that has been proven to be less valuable. Get the seed in the ground and crop up, put out some N-Rich strips. Let the weather play out for a month or so and see 1) Do I have soil moisture to get me through harvest or am I living day by day on a hope and a prayer? 2) is my N-Rich strip showing?

For Question 1) if your living day to day is further investment in the crop warranted? If you have soil moisture and rain in the forecast, its time to rock and roll. For question 2) which I hope you take my advice on doing. If the N-Rich is showing up 30 days into the you can use some rough yield goal estimations and apply 1 lb N per bushel or go get access to a GreenSeeker sensor (available through OSU extension offices) and use OSU’s online calculator SBNRC. If the strips not showing up then you need to consider that a month into the crops growth the soil has supplied 100% of the crops N need. Depending on if you want to push yield or save N adjust your rec accordingly. I would say reducing planned N rate by 40-50 lbs would a legitimate option. There are more and more agronomist utilizing N strips in wheat and sorghum so you could check around.

Final thoughts.
The more I do research on N timing and N management the more I am finding that there are some great benefits to limiting early N availability to the crop. To the point were I am finding and increasing value of an early season N stress on crop performance and grain yield.

Now for rehashed research. Much like wheat, sorghum can and probably should wait for N.

Can Grain Sorghum Wait on Nitrogen? One more year of data.

Original Posting 4.7.2022

Michaela Smith, Ph.D. candidate under advisement of B. Arnall
Brian Arnall, Precision Nutrient Management Specialist

The impressive ability of sorghum to recover from significant N stress with late applied nitrogen was originally reported in the blog “Can grain sorghum wait on nitrogen”. This projected was replicated again in 2021 and these are the results. During the 2021 growing season, frequency of rainfall events and amounts were similar to the 2020 growing season. Figure 1. shows the application dates and rainfall events.

Statistically there was no significant difference in grain yield from the pre-plant (0) and any application up to the 56 day application. This data matches up quite well the yield results from 2020.

Looking and the current soil moisture conditions (Figure 3.) and fertilizer price I think this data supports the recommendation to get the seed in the ground and see how the situation plays out. If there are decent rains at and shortly after planting then there is time to apply nitrogen with little risk of yield loss. If fact the weather during late May and early June provide some of the best chances to getting the fertilizer rained in (Figure 4) . If the weather doesn’t cooperate and provide us the much needed rains, then by waiting to apply we are not left with a lot of Expensive nitrogen setting out in the field of a failed crop.

Final Thoughts Heading into the 2021 Sorghum Planting Season.
– Make sure you have a soil sample, knowing P and K will be critical.
– No need to front load N fertilizer, especially if soil moisture is short.
– Utilize in-furrow P if soil pH and or soil test P is low.
– If you skip pre-plant N APPLY N-RICH STRIPS!!!!
– If you apply pre-plant N consider applying 50% of the expected N or less.
– If you are applying any level of pre-plant N, Create Zero-N Strips.

For more information or questions contact
Brian Arnall b.arnall@okstate.edu 405.744.1722

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

Original Post March 22, 2022.
Data for this post available in thesis Impact of delayed nitrogen application in grain sorghum
Smith, Michaela Lynn (2021-05). Available at https://shareok.org/discover

            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.

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.

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 21^st (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.

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.

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 EDC Ag Products Co LLC for support of this project.