Nitrogen fertilizer is one the most costly crop inputs following seed, and is also quite important for insuring top corn yields. In addition, nitrogen that doesn’t get taken up by a growing corn crop can cause environmental concerns. For these reasons, growers should be concerned with managing this valuable resource carefully. In this educational video Liqui-Grow's agronomy research lead will discuss evidence based research comparing fall vs spring nitrogen sources effects on corn yields and farmer profitability.
Following the 4R’s of nutrient stewardship (the right placement, timing, source and rate) will often lead farmers toward greater crop yields and higher nutrient use efficiency.
Applying nitrogen fertilizer for corn production in the spring vs the fall is a great example of the “right” time.
Science based studies conducted by the University of Illinois, Minnesota State University and by Iowa State University shows on average a 7.9% yield increase for spring vs fall nitrogen applications
Economically these studies clearly show that spring applied nitrogen is the most economical decision for Midwestern corn farmers. In some cases, growers might be able to increase their per acre profit by $43/ac by switching from fall to spring nitrogen sources.
Environmental Stewardship is essential to what we do at Liqui-Grow. We are extremely committed to helping farmers gain more crop yield per dollar spent on fertilizer while also protecting the environment. Since this is a mission at Liqui-Grow, we’ve decided to take part in the Nitrogen Grand Challenge.
What is the Nitrogen Grand Challenge?
The Nitrogen Grand Challenge, hosted by Tulane University in New Orleans, Louisiana, invites competitors that will provide new and innovative ideas to farmers on managing nitrogen fertilizer for maximum profits and environmental sustainability. The competitors are graded by a formula that incorporates production cost, crop yield, and nitrogen use efficiency; which are all key components of a cost-effective, sustainable nitrogen management program.
There are 3 Phases:
Contestants submit their ideas.
Five best ideas get battle-tested. The five best solutions will go into the ground to see if their idea works on a farm in Northeast Louisiana. They will each get a plot of land to test their specific technology during an entire growing season.
Knockdown drag out fight between two finalists. Judges will determine the winner from the top two contestants.
What is the problem?
“Throughout the world, increasingly fragile coastal and inland lake ecosystems face a common and persistent threat; “dead zones” caused by hypoxia continue to challenge the integrity and productivity of environments that are home to a diverse biota and highly valued natural resources. Dead zones result from excess nutrients flowing from rivers to near-shore areas. Though hypoxia is often thought of as a challenge particular to the northern Gulf of Mexico, dead zones are a problem of global proportions.”
“Hypoxia occurs when the oxygen required to support life becomes depleted, which can result in severe impairment of near-shore fisheries. Consequently, dead zones can also destabilize the businesses, families, and communities that are sustained by fisheries. Further, nutrient enrichment can jeopardize the future of estuaries and coastal wetlands that depend on freshwater and sediment delivery for stability and persistence. In short, clean water is critical to the ecological, cultural and economic well-being of Louisiana, the nation, and the world.”
Liqui-Grow feels strongly about their customers’ return on fertilizer investment. A high return on every dollar spent on fertilizer often goes hand-in-hand with high nutrient use efficiency and Environmental Stewardship.
As part of our commitment, Liqui-Grow has enlisted their Agronomy Research Lead, Jake Vossenkemper, to participate in the Nitrogen Grand Challenge. Jake is participating on team CropSmith. They have used their innovative ideas on how to manage nitrogen more efficiently to beat hundreds of other teams. They are now competing in the second round of the Nitrogen Grand Challenge against 4 other teams. The winning team will receive a grand prize of one million dollars, but more importantly, they may lead to groundbreaking concepts of nitrogen management that will lead to greater farmer profitability and environmental sustainability.
Ortho-phosphates are 100% plant available, but a high percentage of poly-phosphates in starter fertilizers convert to ortho-phosphate within just two days of application.
This quick conversion from poly- to ortho-phosphate suggests expensive “high” ortho starter fertilizers are not likely to result in increased corn yields compared to seed-safe fluid starters containing a higher percentage of poly-phosphate.
A field study conducted near Traer, IA in the 2016 growing season found less than 1 bu/ac yield difference between a 50/50 ortho:poly starter and high ortho-phosphate starter.
High ortho starters cost more per acer than 50/50 ortho:poly starters, but do not increase corn grain yields.
Poly-phosphates Rapidly Convert to Plant available Ortho-Phosphates
Given poly-phosphates are not immediately plant available and ortho-phosphates are immediately plant available, this gives the promoters of “high” ortho-phosphate starters ample opportunity to muddy the waters. Nevertheless, the facts are that poly-phosphates are rather rapidly hydrolyzed (converted to) into ortho-phosphates once applied to soils, and this hydrolysis process generally takes just 48 hours or so to complete.
In Sept. of 2015, I posted a blog discussing some of the more technical reasons why the ratio of ortho- to poly-phosphates in starter fertilizers should have no impact on corn yields. For those that are interested in those more technical details, I encourage you to follow this link to the Sept. 2015 blog post: https://www.liqui-grow.com/farm-journal/.
While I was relatively certain that the ratio of ortho- to poly-phosphates in liquid starters should have no effect on corn yields, I decide to “test” this idea with a field trial in the 2016 growing season conducted near Traer, IA.
How the Field Trial Was Conducted
In this field trial, we used two starter products applied in-furrow at 6 gal/ac. Each starter had an NPK nutrient analysis of 6-24-6. The only difference between these two starters was the ratio of ortho- to poly-phosphate. One of these starters contained 80% ortho-phosphate and the other contained just 50% ortho-phosphate with the remainder of the phosphorous source in each of these two starters being poly-phosphate. Each plot was planted with a 24-row planter (Picture 1) and plot lengths were nearly 2400 ft. long. In total, there were 5 side-by-side comparisons of the two starter fertilizers that contained different ratios of ortho- to poly-phosphates.
Field Trial Results
In general, there were no large differences in yield between the two starters in any of the 5 side-by-side comparisons, except for comparison number 5 (Figure 1). In comparison number 5, the 50% ortho/50% poly-phosphate starter actually yielded 6 bu/ac more than the high ortho starter. But averaged over the 5 side-by-side comparisons, there was less than 1 bu/ac yield difference between the high and low ortho starters (P=0.6712).
In addition to finding no differences in grain yield between these two starters, the high ortho starters generally cost about $1 more per gallon (so $6/ac at a 6 gal/ac rate) than the low ortho starters. So the more expensive high ortho starter clearly did not “pay” its way in our 2016 field trial.
More Trials Planned for 2017
While our findings agree with other research-comparing ortho- and poly-phosphate starter fertilizers (Frazen and Gerwing. 1997), we want to be absolutely certain that our fertilizer offerings are the most economically viable products on the market. Therefore, I have decided to run this same field trial at one location in northern Illinois in 2017, and at one location in central Iowa in 2017. Stay tuned for those research results this fall.
Planting starter fertilizer trials near Traer, IA in the growing season of 2016.
5 side-by-side comparisons of corn yield from two 6-24-6 starter fertilizers that contained either 50% ortho & 50% poly-phosphate or 80% ortho and 20% poly-phosphate. The field trial was conducted near Traer, IA in the growing season of 2016.
SDS is a frequent disease of soybean, but it does not reduce yields every year—suggesting that ILeVO will be used as insurance-based management.
Using ILeVO increased yields in all 7 on-farm trials in the 2016 growing season.
The average yield increase across all 7 trials was 7.8 bu/ac resulting in net returns of $63/acre (Figure 1).
The economic optimum seeding rate averaged across these particular 7 locations was 127,000 seeds/ac, but seeding up to 140,000 only reduced partial profits by $2/ac—so it seems that over seeding is still cheap insurance against conditions that can significantly reduce stands.
Average soybean yield for plots treated with base fungicide+Insectcide seed treatments and base fungcide+insecticide+ILeVO seed treatments at 7 on-farm sites in Illinois and Iowa in the growing season of 2016.
Sudden Death Syndrome (SDS) is a fungal root rot of soybeans that can routinely cause reduced soybean yields in the U.S. Midwest. Soybeans are most susceptible to SDS within a few weeks after planting, presumably because it is easier for the SDS pathogen to penetrate young succulent root tissue vs. older root tissue that has had time to develop more ridged, less penetrable cortical tissue. Given this early season susceptibility, crop scientists have been searching for a seed-applied fungicide that controls the SDS pathogen.
Since about 2012, Bayer CropScience has been testing a seed-applied fungicide (a.i. fluopyram) that shows promise at reducing soybean SDS infection and yield losses associated with this disease. This seed-applied fungicide, as of the 2015 crop season, has been sold commercially under the trade name ILeVO. In addition to controlling SDS, the ILeVO that is treating the plants has also been shown to have fewer soybean cyst nematodes (SCN) per gram of root than plants with no ILeVO treating (Zaworski, 2014), and is currently being labelled for control of SCN.
Given that ILeVO controls SDS and SCN, this new seed treatment could dramatically increase soybean yields and provide significant financial benefits to Midwestern farmers when these diseases are at high enough levels to reduce yields. Since it is not always known, however, if these diseases will reduce yields at planting, ILeVO may be viewed as insurance-based management in the event that these diseases do reduce yields.
Another insurance policy that farmers have used over the decades is to plant more soybean seeds than necessary to produce maximum economic returns. Over seeding provides insurance against significant stand loss that can often occur from poor planting conditions or wet, cold soils that may materialize soon after planting. Recent research, however, shows that soybean economic optimum seeding rates (EOSR) may be as low as 100,500 seeds per acre when fungicide and insecticide seed treatments are used (Gasper et al., 2015), and is well below the current seeding rates that most Midwestern farmers use on their production acres.
Presented with the aforementioned information, it is possible that farmers may be able to reduce their current seeding rates in an effort to help pay for the added cost of the ILeVO ($10-to-$13/140k unit) seed treatment, in effect, trading dollars spent on an over seeding insurance policy for insurance against SDS and SCN.
To help answer these important economic questions, Liqui-Grow implemented some experiments in the 2016 growing seasons to investigate if the EOSR in on-farm trials is as low as some recent research suggests (100,500 seeds/acre), and to see how often buying an insurance policy against SDS and SCN (ILeVO) pays off.
The Applied Questions
Is the EOSR as low as 100,500 seeds/acre in on-farm trials, and is the EOSR different for seeds treated with base fungicides+insecticide vs. base fungicides+insecticide+ILeVO?
How often does ILeVO increase yields, and is the yield increase large enough to pay for the added cost of the ILeVO seed treatment?
How Were the Applied Questions Answered?
Four on-farm studies were implemented in eastern, IA and 3 in northern, IL. At each of these sites farmer cooperators seeded soybean at 50,000-to-150,000 seeds/acre in 25,000 seed increments. Half of each of these seeding rate plots were treated with base fungicides+an insecticide seed treatment. The remaining half of each of these seeding rate plots were treated with base fungicides+an insecticide+ILeVo seed treatments.
Plot widths ranged from 30-to-80 ft wide, and plot lengths ranged from 230-to-2,260 ft long. All sites were productive prairie-derived mollisols except for the Peoria, IL site; this site had sandy loam soils and was irrigated.
Calculating the EOSR
For calculating the EOSR, it was assumed that the seed cost was $82/140k unit for the base fungicides+insecticide treated seeds and $96/140k unit for the base fungicides+insecticide+ILeVo treated seeds. It was also assumed that farmers received $10 for each bushel of soybean sold.
All varieties used in these studies were Credenz brand soybeans marketed and sold by Bayer CropScience, and they had average to above average SDS tolerance ratings.
At 6 of the 7 sites, SDS symptoms—chlorotic mottling and leaf chlorosis—were present during the seed-filing period (R6), and these symptoms were almost always more severe in the control plots that did not have seeds treated with ILeVO (Picture 1).
Averaged across seeding rates, yield increases for the ILeVO treated seeds ranged from 3.2-to-15.4 bu/acre (Table 1). Moreover, sites that had more severe SDS symptoms during the seed-filling period tended to have larger yield increases from adding ILeVO to the base fungicides+insecticide seed treatment package. An exception to this was the Clear Lake, IA site. At this site no SDS symptoms were visible during the seed-filling period, but on average ILeVO increased yields 5 bu/acre.
The EOSR for the base fungicides+insecticide seed treatments was 126,000 seeds/acre and the EOSR for the base fungicides+insecticide+ILeVO seed treatments was 128,000 seeds/acre averaged over the 7 sites (Figure 2). Moreover, the EOSR in these studies was about 25,000 seeds/acre higher than what the most recent published research suggests (Gasper et al., 2015).
– – – – – – – – Grain Yield bu/ac – – – – – – – –
Clear Lake, IA
West Liberty, IA
Soybean yields and net returns from using base fungcide+Insectcide or base fungcide+Insectcide+ILeVO seed treatments at 7 Illinois and Iowa locations in the growing season of 2016.
Averaged across these 7 sites, adding ILeVO to a base fungicide+Insectcide seed treatment package increased yields 7.8 bu/acre and economic returns $63.1/acre. This suggests that ILeVO may be a worthwhile insurance policy for farmers to purchase.
Even though there is not a guarantee that ILeVO will provide a return on investment in every season’s yield, increases such as these in 2016 suggest that ILeVO could be bought for the next 5 growing seasons and net returns would still be north of break even.
That being said, the odds are high SDS will return again in one or several of the next 5 growing seasons. While this specific data set does show that the EOSR is around 127,000 seeds/acre—still lower than the avg farmer seeding rate—it still may be a wise insurance policy to seed closer to 140,000 seeds/acre, given it is difficult to predict when significant stand loss will occur, and seeding 140,000 vs. 127,000 seeds/acre only lowered partial profits by $2 per acre in these studies.
Can nitrogen models increase net revenues when compared to traditional N management rates? What about when compared to an N rate recommendation from the Corn N Rate Calculator? Several Midwestern land grant universities conducted a study to test this theory.
The nitrogen management model produced the lowest net revenues. These net revenues were $21. They were $27/acre lower than the net revenues produced by the growers’ traditional N management rates and the N rate recommended by the Corn N Rate Calculator.
While nitrogen management models may become more accurate with time, this study suggests that for now growers should proceed with caution before adopting N management models for wide-scale use.
Within the last few years, nitrogen management models seem to be all the rage. DuPont Pioneer promotes Encira Yield Nitrogen, Monsanto has Climate-N, and Agronomic Technology offers Adapt-N. This is a short list of the Big 3, but there are still the droves of Silicon Valley start-ups promising to solve all our nitrogen management woes.
The idea behind these N models is stellar: use less fertilizer N in years with low nitrogen loss conditions and more fertilizer N in years when more N loss has occurred. Potentially, this could reduce N pollution, save on fertilizer N costs, or increase yields in years when more fertilizer nitrogen is required.
This is, of course, the utopia for which the agricultural industry has been searching.
I am sure the aforementioned corporations have hired the best in the business to take on such a monumental task and that they are using the most advanced statistical models known to man. However, Mother Nature—and the complexities of the nitrogen cycle—will put up a formidable fight.
I can only hope that they have been successful. Answering these complex questions would be a win for farmers, for the agricultural industry, and for the general public. But are these nitrogen management models currently being sold to farmers ready for the “big league?” Can these nitrogen management models help farmers make better business decisions as soon as the 2017 crop season? The answer to that question still isn’t clear.
This past crop season, Liqui-Grow implemented experiments to give both us and our customers some clearer answers to this important question.
Can a nitrogen management model recommend an N rate that results in net profit gains compared to growers’ traditional N management rates?
Can a nitrogen management model recommend an N rate that results in net profit gains compared to the Corn Nitrogen Rate Calculator developed by several Midwestern land grant universities?
Answering the Applied Questions
In southeast Iowa, nitrogen fertilizer rates ranging from 0-to-250 lbs of N/acre were applied to three different farmers’ fields. It was applied in approximately 50 lbs increments. In each of these three fields, these nitrogen rates were replicated 3 times. Soybeans were the previous crop for each field. Each N rate plot was 30 ft wide and approximately 300 ft long.
Most of the nitrogen was applied at the V-7 growth stage, dribbled on the soil surface as liquid UAN 32%. At each of these fields, the soils were highly productive, prairie derived mollisols with OM ranging from 3.3-to-3.8%.
At the request of the developer, the specific nitrogen model used will remain anonymous. It did, however, come from one of the Big 3.
The profitability from any N rate (or any N recommendation system) can be calculated by applying a wide range of N rates, as we did in these studies. Of course, this depends on the yield that any given N rate produced and the amount of nitrogen it took to produce that yield.
For the economic calculations, $0.39/pound of N was used. The price for a bushel of corn was assumed to be $3.50.
How Did the N Recommendation Systems Compare?
In the interest of being short and sweet, I will only discuss what happened on average across these three different trials. Nevertheless, I have included the results from each of the three locations in Table 1.
Therefore, on average, these three growers typically apply 170 lbs of N/ac when corn follows soybeans. The Nitrogen Rate Calculator, developed by several Midwestern land grant universities, recommended 149 lbs of N/ac, and the N model recommended 136 lbs of N/ac.
In spite of the growers applying 21 more lbs of N/ac than the N Rate Calculator recommendation, the yields between these two N rates were nearly identical. The grower-chosen N rate produced a yield of 230.4 bu/ac and the N Rate Calculator recommendation produced a yield of 229.6 bu/ac. The N model, however, recommends applying 34 and 13 less lbs of N/ac than the grower selected N rate and the N Rate Calculator recommendation. Therefore, the N model recommendation produced approximately 10 fewer bu of corn/ac than either the grower-selected N rate or the N Rate Calculator recommendation (Figure 1).
The N model recommendations reduced the N cost by a few dollars/acre. However, the lost yield meant that the N model had the lowest net revenue, at $719/acre. The grower-selected N rate and the N Rate Calculator recommendations followed, producing net revenues of $740 and $746/acre.
So, are these N models ready for the “big league?”
With the current commodity climate, I think most farmers will find it hard to gut an extra $27/acre, not to mention access to these N models is not free. No doubt, these N models will likely get more accurate with time. While that happens, however, this small investigation that evaluated only one of these N models would suggest that growers should proceed with caution.
Liqui-Grow will likely continue to evaluate these N management models, so stay tuned for further updates next fall.
Net revenue from grower-selected N rates, Corn N Rate Calculator recommended N rates, and an N rate prescribed by an N management model at 3 southeast Iowa locations in 2016.
Nitrogen rates and corn yields at three different southeast Iowa locations in the growing season of 2016. Round markers represent the grower-selected N rates. Triangle markers represent the N rates prescribed by a nitrogen management model.
Soil temperatures are finally approaching the mid 50’s across the state of Iowa after an unusually warm Sept. and Oct. This suggests that many more growers across the state may soon start applying fall anhydrous ammonia for the 2017 crop.
After seeing the results of a 3-year study conducted by Iowa State University, I was again reminded that the economic penalty associated with fall anhydrous applications far outweigh the conveniences of this practice.
Downsides to Fall Anhydrous Applications
Fall anhydrous ammonia application timings required 54 more lbs/N per acre to maximize economic returns, and yielded 6% less when compared to spring or early side-dress N applications timings.
Lost yields and substantially higher N requirements for the fall anhydrous applications meant economic losses of $47.10/acre when compared to the spring or early side-dress N application timings.
Economic Optimum Nitrogen Rates and Application Timing
Last week I was in Des Moines, IA, at the North Central Extension-Industry Soil Fertility Conference. At this conference, Dr. John Sawyer (ISU’s Soil Fertility Specialist) brought some data to my attention that I wanted to share.
Dr. Sawyer presented some research results regarding the impacts of nitrogen timing effects on corn grain yields and economic optimum nitrogen rates (EONR). In this research, Dr. Sawyer applied N rates from 0-to-200 lbs/N per acre at 3 different timings: in the fall after soil temps fell below 50 degrees F, as a pre-plant application, and at an early side-dress timing (V4). Dr. Sawyer did this for 3 seasons in central IA, the previous crop was always soybean and the nitrogen source for all 3 N application timings was anhydrous ammonia.
Averaged over the 3 seasons of the study, Dr. Sawyer found that the EONR for the fall applied anhydrous ammonia was 200 lbs/N per acre, but for the spring pre-plant N application and the early side-dress N application timings the EONR was about 146 lbs/N per acre. What’s more, corn that received all fall applied N had yields that were 6% lower than the corn that was side-dressed or had all the N applied prior to planting in the spring.
I wish I could say I was surprised by Dr. Sawyer’s findings, but I was not. What Dr. Sawyer shows here is not new, other University studies over the years have reached similar conclusions, and when you use data sets like this to make some simple economic conclusions, it appears that what initially seemed “cheap” and “easy,” may not be so cheap after all.
Economics for Different N Application Timings
To elaborate on the economics of these nitrogen timing practices, Table 1 shows that applying N as either a pre-plant or early side-dress N application is $47.10/acre more profitable than fall anhydrous ammonia applications.
To reach this conclusion I used the EONR found in Dr. Sawyer’s latest research for the pre-plant/side-dress (EONR = 146 lbs/N ac) and fall (EONR = 200 lbs/N ac) applied N application timings. In addition, I assumed that the fall anhydrous ammonia application timing yielded 6% less (188 bu/ac) than the pre-plant or side-dress N application timings (200 bu/ac), and that the price received for a bushel of corn was $3.50. Lastly, I assumed the fall anhydrous cost $0.31/lb of N and spring or side-dress sources of N cost $0.39 per/lb of N (typical price spread for AA bought in the fall vs. UAN that would be applied pre-plant or in-season).
What Table 1 shows makes it very clear which N application timings are more profitable. So, the question really is, “At what economic (to the grower) and environmental price does the convenience of applying N in the fall no longer seem reasonable?”
While lower yields and higher EONR for fall applied N applications are not new, wide-spread availability to high clearance, self-propelled sprayers is new and gives growers yet another reasonable option for applying N in-season.
Fall, spring pre-plant and side-dress anhydrous ammonia application effects on EONR and corn yields. Figure from Sawyer et al., 2016.
Corn yield and profitability from fall applied or pre-plant/side-dress N application timings.
Sawyer, J.E., D.W. Barker, and J.P. Lundvall. 2016. Impact of nitrogen application timing on corn production. North Central Extension-Industry Soil Fertility Conference proceedings. 39:56-60. http://extension.agron.iastate.edu/NCE/index.aspx (accessed 11 of Nov 2016)
The 2015 growing season was rather wet in parts of east-central and south-east Iowa. Most of the above normal precipitation fell in the last half of May and June in east-central Iowa, whereas the wettest two months in south-east Iowa tended to be June and July (Table 1).
Regardless of when the rain fell, this excess precipitation caused saturated soils and nitrogen (N) loss via leaching and denitrification (loss as N2 or N2O to the atmosphere) leading to corn fields with varying levels of N deficiencies.
A wet growing season in east-central and south-east, IA led to many fields with saturated soils and N loss, leaving growers and salesman wondering, “Can this crop be saved with extra N fertilizer?”
Rescue N plots were implemented in three farmers’ fields in eastern, IA to test this idea.
Rescue nitrogen increased profitability over the zero N control $90, $61, and $16 dollars/acre in severely N deficient corn, moderately N deficient corn, and corn that was not apparently N deficient at the time of rescue N applications.
The most profitable N rate in the severely N deficient corn, moderately N deficient corn, and corn that was not apparently N deficient at the time of rescue, N applications was 57.5, 71.5, and 44.3 lbs N/ac.
Rescue N is likely to increase corn yields, but the soil should be given a chance to dry out before attempting rescue N treatments. In other words, applying more N isn’t likely to increase yields if soils continue to stay saturated.
In the field experience
Because of the above normal rain and subsequent N loss, I was asked to visit many fields this summer. A common question from farmers and salesman was, “Can this corn be ‘rescued’ by applying more N?” My response tended to be that the available evidence says it can, but the number of experiments that have been conducted to reach these conclusions are few.
Moreover, we are even less confident that if more N can help this corn crop recover from saturated soils and N loss, how much more N will it take? On top of all this, there is the problem of the nitrogen loss not being evenly distributed across the entire field. In other words, in fields where N loss is caused by standing water—denitrification primarily—it is very common for there to be severely N deficient corn, moderately N deficient corn, and corn that does not appear to be at all N deficient in the same field.
Given these drastic changes in apparent N status of the crop, it would seem plausible that the entire field may not need N—or at least a different rate of N—but that isn’t at this time well-known, either.
It isn’t easy to vary the rate of N across fields such as these. It can be technically done, but the equipment to apply N based on crop canopy color isn’t widely available. As you can see, there are many questions to be asked and few available answers. In addition, these questions have important financial ramifications for farmers, and applying more N that doesn’t result in financial gains will result in environmental pollution. So the main questions we set out to answer are as follows.
Can applying more N to corn that’s been previously fertilized and exposed to several days of saturated soils and N loss result in a net profit increase?
If so, how much additional N does it take?
In these situations, should the whole field receive additional N, or just parts of it?
How Were the Applied Questions Answered
To answer these questions, we established replicated rescue N rate plots in three different farmers’ fields. All three fields were in Clinton county Iowa, two near the town of DeWitt, and the third close to Andover. Each of these fields had been fully fertilized with N prior to the establishment of these experiments, and the N rates prior to the initiation of these experiments ranged from 179 to near 200 lbs N/ac. In each of these three fields there were three separate N rate plots established. One in what appeared to be severely N deficient corn (stunted completely yellow corn), moderately N deficient corn (normal height but with the classic inverted V-shaped yellow chlorosis in the lower canopy leaves), and corn that did not appear to be N deficient (corn was normal height, and green from top to bottom) when the experiments were initiated.
In each of these levels of N deficiency there were 6 treatments, 4 evenly spaced N rates from 30 to 120 lbs N/ac and a control (zero N applied). Moreover, one treatment was 30 lbs N/ac plus 15 lbs of sulfur per acre. The sources of N and sulfur were liquid urea ammonium nitrate and ammonium thiosulfate dribbled on the soil surface.
The experiments at each field were established just prior to or after the beginning of reproductive growth (VT/silking). So that you can envision the differences between the severely, moderately, and no apparent levels of N deficiency, I have included a table with the average plant height, average number of green leaves per plant, and the nitrate nitrogen in ppm in the top 2 ft of soil prior to the initiation of the experiments.
Lastly, below are three pictures (picture 1) taken in the same field and at similar distance above the soil surface showing the drastic difference in crop height between the severely deficient, moderately deficient, and corn that did not appear to be N deficient.
The three different levels of N deficiency symptoms where N rate trials were established at one grower’s field in east-central, IA. From left to right is the severe, moderate, and corn that had no apparent N deficiency symptom at the time of experiment initiation. The dedicated intern in these photos (Ryan Cruise) who helped establish these plots is approximately 5’7” tall.
In these experiments, applying more N to corn that had been previously fertilized and exposed to several days of saturated soils and N loss clearly resulted in net profit returns. Moreover, at the corn and nitrogen prices used here, applying more N to corn increased net profitability in all three levels of N deficiency.
The nitrogen rate that produced the greatest return to N varied some in the three different levels of N deficiency symptoms. In the severe, moderate, and corn with no apparent N deficiency symptoms, the N rate that maximized economic return was 57.5, 71.5, and 44.3 lbs N/ac (Table 3), producing net profit increases over the zero N control of $90, $61, and $16 dollars per acre (figure 1).
While all three levels of N deficient corn were responsive to rescue N applications, the moderately N deficient corn was the most responsive, producing 32.1 bu/ac more corn with N, followed by N increasing the severely N deficient and corn with no apparent N deficiencies 23.5 and 10.1 bu/ac.
This was not a terribly surprising finding, corn that still has good height and a canopy to capture sunlight probably has the best chance of responding to rescue N applications. On the other hand, corn that has had its height and leaf size severely reduced, and presumably yield potential probably needs less N to reach maximum yield. Corn that does not appear N deficient may not always respond to rescue N applications, but it’s possible that good looking corn (none N deficient) at the beginning of reproductive growth can run out of N, as I suspect happened here.
So should we rescue corn next time we think it needs rescued from standing water and N loss? These results sure tend to suggest that, and they align with some University trials conducted by Dr. Peter Scharf at the University of Missouri.
It’s important to keep in mind that corn roots must be actively taking up mineral nutrients if the rescue N is going to make it in the crop, and to do so corn cannot be in standing water that is depleted in oxygen.
Before applying rescue N, it might be worthwhile to wait for the soil to dry some, and to see if standing water kills large portions of the crop, because applying more N to dead corn—or corn that can’t take up the rescue N—sure won’t help.
The net return to rescue nitrogen fertilizer in severely N deficient corn, moderately N deficient corn, and corn that was expressing no apparent N deficiency symptoms at the time of rescue N applications. The curves are the average response of three east-central, IA rescue N locations in the growing season of 2015. The return to N assumes $3.80 corn and $0.48/pound of nitrogen fertilizer.
The 2015 growing season at the Walcott research farm was wetter and cooler than normal. June and July were particularly wet, with about 14.5 inches of precipitation falling in these two months alone. The wet weather caused periodic ponding and nitrogen loss which was noticeable in the corn, particularly in the lowest laying parts of the farm and during the last several weeks of reproductive development. Despite the wetter than normal weather, corn yields were good, averaging 213 bu/ac. This is 26% higher than the average corn yield in eastern, IA (avg. eastern IA corn yield = 169 bu/ac).
Soybeans were however the champions, yielding 72 bu/ac on average, and is 37% higher than the average soybean yield in eastern, IA (avg. eastern IA soybean yield = 52 bu/ac).
A full rate of Instinct II (37 oz/ac) applied with 130 lbs/ac of nitrogen as a pre-plant dribble band, UAN application increased corn yields a whopping 19.1 bu/ac.
Using Instinct II at either a half or full rate (19 or 37 oz/ac) with 50 lbs of nitrogen as UAN at side-dressing (around V-6) also increased corn yields by about 6.5 bu/ac.
When DKC 61-54 and M2A749 were allowed to naturally cross, they produced yields that were 10.6 bu/ac higher than the solid seeded M2A749 hybrid, and 8.9 bu/ac higher than the solid seeded DKC 61-54 hybrid.
When a different Mycogen (M2V709) hybrid was allowed to cross with DKC 61-54, the plots with the hybrid mix yielded similarly to both the M2V709 and DKC 61-54 solid seeded hybrids.
After analyzing all 7 years of Ken Washburn’s soybean micronutrient trials it was found that manganese sulfate applied at 1.3 lbs/ac with fall dribble banded P & K increased soybean yields 1.95 bu/ac over the untreated check (Pr .0188). At $9.00 soybeans, and after subtracting the $4.50 manganese sulfate cost, this resulted in a net profit increase of $13.05 per acre.
Instinct II – Corn
No surprise, in my mind, given the year, that 37 oz/ac of Instinct II applied with 130 lbs/ac of nitrogen as spring pre-plant dribble band, UAN application increased corn yields a whopping 19.1 bu/ac. Moreover, using Instinct II at either a half or full rate (19 or 37 oz/ac) with 50 lbs of nitrogen as UAN at side-dressing (around V-6) also increased corn yields by about 6.5 bu/ac.
So would we expect yield increases as large as these every year from Instinct II? The answer is no; in some years, particularly those that are dry, we might expect only small or even no yield increases from using Instinct II.
Because Instinct II is a nitrification inhibitor, it temporarily stops the conversion of ammonium (NH4+) to nitrate (NO3 –)—the nitrogen form that is highly susceptible to loss via leaching and denitrification. Therefore, in wet years (like 2015) or on wet farms—or on sandy farms in normal years—we would expect Instinct II to increase yields and profitability.
Using the 19.1 bu/ac yield increase observed in 2015 tells us that at $4.00 corn and $12.00/ac Instinct II cost we could go for 6 consecutive years with no yield increase from Instinct II and still break even. So like many agronomy inputs, Instinct II is not a silver bullet, but is a product that does what it’s advertised to do (slow nitrification) and can reduce production risk and increase long term profitability.
Hybrid Outcrossing – Corn
The idea here was to let two hybrids with a similar number of GDU’s to silking and pollen shed naturally cross by planting 50% of each in the same plot.
When DKC 61-54 and M2A749 were allowed to naturally cross, this produced yields that were 10.6 bu/ac higher than the solid seeded M2A749 hybrid, and 8.9 bu/ac higher than the solid seeded DKC 61-54 hybrid. When a different Mycogen (M2V709) hybrid was allowed to cross with DKC 61-54, the plots with the hybrid mix yielded similarly to both the M2V709 and DKC 61-54 solid seeded hybrids.
These results are similar to other experiments like this in that mixing hybrids did not always increase yields relative to the solid-seeded parents. Yield increases from mixing hybrids that require a similar amount of GDU’s to silking and pollen shed will be dependent on how genetically related the two hybrids are that are allowed to naturally cross.
Manganese – Soybeans
In my 4.5 months here at Liqui-Grow, one of the more common questions has been, “Does manganese increase soybean yields?” This is a good question given that in some universities’ studies manganese does increase soybean yields, but in others it does not. Thankfully, Ken Washburn—now retired Liqui-Grow Agronomist—has been diligent in his pursuit to answer this question.
Running the same randomized replicated trial—replicated 4 or 5 times—on micronutrients for soybeans since 2008 gives us the ability to take a good look at this question over years and different soybean varieties.
After finding the handwritten, raw data in the filing cabinets in my office, I submitted this information to a statistical analysis. Why? Statistics are a good way to understand if the treatment effects—in this case, the effects of manganese on soybean yields—are, in fact, real or just a reelect of natural variation present within fields.
My finding was that manganese sulfate applied at 1.3 lbs/ac with fall P&K increased soybean yields 1.9 bu/ac over the untreated check (P < 0.0188), and, statistically speaking, we are very confident that this did happen. At $9.00 soybeans, and after subtracting the $4.50/ac manganese sulfate cost, this resulted in a net profit increase of $13.05/ac.
I also might add that the Walcott Research Farm is not a place where we traditionally think manganese deficiencies would occur. Based on what we know today, manganese deficiencies are more likely in soils with pHs above 7, in organic soils, and soils that are sandy. However, the Walcott farm fits none of these categories. This data set supports the idea that perhaps manganese deficiencies are more wide spread than we think.
It seems like a funny time of year to debate the agronomic differences between ortho- and poly-phosphates in liquid starter fertilizers. I have been asked this question before, but the question has arisen again.
So what are the differences, and, from a practical perspective, does it matter?
Liquid starters that contain 80-to-100% phosphorus (P) in the ortho-phosphorus form are not agronomically necessary.
Some liquid starters contain 40-to-60% poly-phosphates. However, under most soil conditions, 50% or greater of the poly-phosphates will be hydrolyzed (converted) to plant-available ortho-phosphates in just a few days.
Independent research does not show greater corn yield when P is supplied in the ortho- vs. poly-phosphate form.
In fact, in some P fixing soils, poly-phosphates may actually increase fertilizer P uptake.
Temperature and Phosphate Hydrolysis
Given that ortho-phosphates are much more plant-available than poly-phosphates, an initial glance would lead you to believe starter fertilizers that contain mostly ortho-phosphates may be superior to those that do not.
Thankfully for us, water soluble, liquid poly-phosphates tend to convert to ortho-phosphates rather rapidly when applied to soils. This conversion from poly- to ortho-phosphates is an enzyme-mediated hydrolysis reaction. Therefore, as the soil temperature rises so, too, does the rate at which the conversion takes place.
Even though the hydrolysis process is slower at cool soil temperatures, Chang and Racz (1977) generally found greater than 50% of the poly-phosphates to be converted to the ortho- form in as few as 48 hours at soil temperatures as low as 41°F (Figure 1).
An example “pop up” starter for corn
So getting back to the nuts and bolts of the question, does the percentage of ortho- vs poly-phosphates in liquid starters have any real implications? Using a 6-24-6 starter fertilizer source, and corn as the crop planted in April, let’s see if not having 100% of the P in the ortho- form should even matter.
Given a very conservative 6-24-6 “pop-up” starter fertilizer application rate of 10 lbs/ac of actual P—so about 3.7 gal/ac—and a soil temperature of 50°F at planting, we would expect at least 7.5 lbs of that P to be in the ortho- form within 2 days after planting. We reach this conclusion because about 50% of the P in 6-24-6 is already in the ortho- form—so 5 of the original 10 lbs—and we would expect at least half of the remaining 5 lbs of P in the poly- form to be converted to the ortho- form within about 2 days, bringing us to 7.5 lbs of easily plant available P shortly after the seed was put in the ground.
So, is 7.5 lbs of P enough to meet the initial needs of seedling corn? Well, according to the latest research on modern corn hybrids, V5 corn accumulates less than 5 lbs of P per acre (Bender et al., 2013). By these estimations, corn P mineral nutrient requirements could be met until at least V5 on the plant available P in the modest (3.7 gal/ac) 6-24-6 starter fertilizer application.
Warming soils increase the rate of hydrolysis and P mineralization
Some may argue that portions of the P in initial starter fertilizer applications will be fixed by the soil and made unavailable to growing plants. This is true in some cases, but I would argue that banded applications tend to be pretty efficient. Moreover, by V5, the soil has warmed considerably, allowing organic forms of P to be mineralized and to become plant-available.
Along with warming soil causing organic P availability, this would further promote the hydrolysis of the remaining poly-phosphorus in the initial liquid starter application. In addition, by V5, we would expect corn to have transitioned almost entirely to the nodal root system, and thus, would be exploring soil resources other than those provided by the initial starter application.
In addition to it not making good sense, the research on this topic conducted by independent sources appears not to support this idea (Table 1) (Frazen and Gerwing, 1997). Some new and independent research would even suggest that ammonium poly-phosphate results in increased P uptake when compared to fertilizer sources that contain more ortho-phosphates (Table 2). The increased P uptake with ammonium poly-phosphate seems to be most prevalent in soils with the ability to fix substantial amounts of fertilizer P. In these cases, we believe keeping P temporarily in the poly form reduces the amount of fertilizer P that can be fixed into forms that are more permanently unavailable for plant uptake (Torres-Dorante et al., 2006). A clear topic of interest, but one we will save for a different time.
Temperature effects on hydrolysis of water-soluble (A and B)
sodium pyrophosphate (a ploy-phosphate) and (C and D) sodium
tripolyphosphate (a more complex poly-phosphate) to ortho-phosphate.
Torres-Dorante, L.O., C. Norbert, B. Steingrobe, and H.W. Olfs. 2006. Fertilizer-use efficiency of different inorganic polyphosphate sources: effects on soil P availability and plant P acquisition during early growth of corn. J. Plant Nutr. Soil Sci. 169:509-515.
Chang, C. and G.J. Rncz. 1977. Effects of temperature and phosphate concentration on rate of sodium pyrophosphate and sodium tripolyphosphate hydrolysis in soil. Can. J. Soil Sci. 57:211-278.