New Research Comparing Ortho/Poly-Phosphate Ratios

 

Blog Banner for Poly Phosphate study

Summary

  • Ortho-phosphates are 100% plant available, but a high percentage of poly-phosphates in starter fertilizers convert to ortho-phosphate within just two days after 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 conventional poly-phosphate starters.
  • On-farm field studies conducted near Traer, IA and Walnut, IL from the 2016 to 2018 growing season found no statistical difference (Pr > 0.05) in corn yield between conventional and high ortho-phosphate starters.
  • High ortho starters cost more per/ac than conventional poly-phosphate 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, poly-phosphates are rather rapidly hydrolyzed (converted to) into ortho-phosphates once applied to soils, and this hydrolysis process generally takes just 48 hrs 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 the more technical details, I encourage you to follow this link to
the Sept 2015 blog post (liqui-grow.com/farm-journal).

While we were 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 on-farm field trials located near Traer, IA and Walnut, IL  in the 2016, 2017 and 2018 growing seasons.

tractor planting fertilizer

Picture 1. Planting starter fertilizer trials near Traer, IA in the growing season of 2016.

 

How the Field Trial Was Conducted

In these field trials we used two starters applied in-furrow at 6 gal/ac. Each starter had a NPK nutrient analysis of 6-24-6. The only difference between these two starters was the ratio of ortho to poly-phosphates. 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. At the Traer, IA locations the plots were planted with a 24-row planter (picture 1) and were nearly 2400ft long. At the walnut, IL locations the research was conducted using small plot techniques, plot dimensions there were 10 ft wide by 30 ft long. At both Traer, IA and Walnut, IL in each of the 3 growing season the experimental design used was a simple randomized complete block with 4 or 5 replications.

Figure 1. Average corn yield from field trials comparing high ortho vs conventional poly-phosphate in-furrow seed safe starter fertilizers. Yields at each location/year are averaged over 4 or 5 replications.

 

Figure 2. Partial profit from field trials comparing high ortho vs conventional poly-phosphate in-furrow seed safe starter fertilizers. Yields at each location/year are averaged over 4 or 5 replications. Partial profit was calculated using a grain sale price of 3.50 bu. Cost per gal used to calculate partial profit for the 6-24-6 50% ortho & 50% poly-phosphate and 6-24-6 80% ortho & 20% poly-phosphate was $2.80 and 3.20 per/gal

 

Field Trial Results

Averaged over the 5 site-years there was only about 1.5 bu/ac yield difference separating the high ortho and conventional poly-phosphate starter (figure 1). Moreover, this small yield difference was not statistically significant (Pr > 0.05). In addition to finding no differences in grain yield between these two starters, the high ortho starter cost about $0.50 more per/gal (so $3/ac difference in price at a 6 gal/ac rate) than the lower ortho starters. So the more expensive high ortho starter clearly did not “pay” its way in our multi-location field trials (figure 2). Lastly, our observations in these studies agree with previously published university findings (Frazen and Gerwing. 1997).

References

Franzen D. and J. Gerwing. 2007. Effectiveness of using low rates of plant nutrients. North Central regional research publication No. 341. http://www.extension.umn.edu/agriculture/nutrient-management/fertilizer-management/docs/Feb-97-1.pdf (accessed 8 of Sept 2015).

 

– Dr. Jacob Vossenkemper (Agronomy Research Lead)

Urea – A Poor Choice of Nitrogen Fertilizer for In-Season N Applications

John Deere tractor in corn field

 

Summary

  • Urea fertilizer, if not incorporated by tillage or precipitation, is highly susceptible to ammonia volatilization (loss to the atmosphere as ammonia gas).
  • Uniform application of urea can be problematic due to segregation of larger and smaller urea prills and due to physical spread pattern interference from standing corn during in-season applications.
  • Liquid UAN (32 or 28%) is only 50% urea and is about half has susceptible to ammonia volatilization as dry urea.
  • Banding UAN further reduces the probability of nitrogen loss via ammonia volatilization.
  • Averaged over 3 on-farm plots side-dressing surface banded UAN gave 16.2 $/ac greater net returns and yielded 5.5 bu/ac more than surface broadcasted urea.

Urea, anhydrous ammonia and liquid urea ammonium nitrate (UAN 28 or 32%) are by far the most common sources of nitrogen fertilizer used in corn production. Moreover, all 3 sources of nitrogen fertilizer have their own unique advantages and disadvantages, but in particular, dry urea is an exceptionally poor source of nitrogen for in-season applications to corn. At first glance, urea seems to be an attractive in-season nitrogen source, because it can be applied rapidly with high clearance dry spinner spreaders and urea is commonly a few cents per lb of nitrogen cheaper than UAN. Urea, however, is highly susceptible to N loss via ammonia volatilization and uniform fertilizer nitrogen distribution can be a serious problem for top yields and maximizing economic returns.

Dry Urea: Elevated Risk for N Loss via Ammonia

Ammonia volatilization occurs when the urease enzyme hydrolyzes urea fertilizer to ammonia on the soil surface. Given ammonia (NH3) is a gas and lighter than air, the ammonia literally floats away into the atmosphere. The most effective way to prevent ammonia volatilization is for urea hydrolysis to occur beneath the soil surface where the ammonia gas can interact with hydrogen ions to form ammonium (NH4+).

To avoid serious N loss, urea must be incorporated with tillage, moved below the soil surface by precipitation or subsurface injected. For in-season N application, however, physical incorporation or injection of dry urea is not practical, leaving a rainfall event that must exceed 0.5 inches to move the urea below the soil surface (figure 1). This significant rainfall event must occur no later than 4 days after urea application (figure 2) or N loss from ammonia volatilization could drastically accelerate in subsequent days (Jones et al., 2013). UAN is also susceptible to ammonia volatilization, but only 50% of the nitrogen in UAN is urea. Therefore, UAN is roughly half as susceptible to ammonia volatilization as dry urea.

irrigation rate graph

UAN also provides more flexibility regarding in-season applications than dry urea. UAN can be subsurface injected or surface banded within the row. Subsurface injection of UAN strongly reduces the potential for ammonia volatilization because urea hydrolyses occurs below the soil surface. Banding UAN on the soil surface does not eliminate ammonia volatilization, but reduces the risk of ammonia volatilization considerably (figure 2, Jones et al., 2013). The reduction in ammonia volatilization risk with banding UAN occurs because banding physically reduces the amount of N fertilizer exposed to the urease enzyme.

Field with low Urea rate stripes

Poor Fertilization: Increases Yield Loss Risk

Achieving uniform application with dry fertilizer, which includes urea, can be a difficult task. Several problems exist that can lead to non-uniform urea applications. If urea is not uniformly sized, the result is segregation of larger and smaller urea particles during loading, transportation to the field and during spreading. Particle segregation is a problem because larger urea granules are thrown further from the dry spinner spreader machine than smaller particles, resulting in a higher application rate directly behind the machine and a lower applications rate at the edges of each pass.

Segregation is not the only concern. When side-dressing corn, poor urea distribution can be exacerbated by the standing corn crop, particularly when corn reaches over a few feet in height. Tall corn acts as a funnel, cutting down the distance at which the urea granules can be thrown compared to when no crop was present to disrupt the flow of urea toward the edges of each pass.

On-Farm comparisons: Broadcast Urea vs. Surface Banded UAN as In-Season N Sources

The on-farm studies were conducted at 3 locations in the 2016 growing season. The locations included Elkhorn, WI, Tipton and Morning Sun, IA. The base and side-dress N rates used at each location are listed in table 1. At each location the side-dress nitrogen was applied at growth stages between V6 to V8 as either surface banded UAN or surface broadcasted urea. At each location these treatments were replicated 3 or 4 times. The price of UAN and urea used to calculate partial profit was 0.36 and 0.32 $/lb N. The price of corn used to calculate partial profit was 3.50/bu.

Surface Banded UAN vs Surface Broadcasted Urea chart

Averaged over the 3 locations yields were increased 5.5 bu/ac from surface banded UAN when compared to surface broadcast urea (table 2 and figure 3). In addition to higher yields from surface banding UAN vs broadcasting urea, net profits were 16.2 $/ac higher for the surface banded UAN treatments, despite slightly higher nitrogen costs (table 3).

Table 1table 2table 3

Summary

Because urea cannot be physically incorporating post-planting, it is susceptible to loss via ammonia volatilization (loss to the atmosphere as NH3 gas). Moreover, uniform application with dry fertilizer, including urea, can be problematic due to segregation of larger and smaller urea prills and due to physical spread pattern interference from standing corn. For these reasons, urea is a particularly poor source of nitrogen fertilizer for in-season applications. In these 3 on-farm trials surface banding UAN increased yields 5.5 bu/ac and net profits 16.2 $/ac compared to surface broadcasting dry urea.

Reference

Jones, C., B.D. Brown, R. Horneck, D. Olson-Rutz. 2013. Management to Minimize Nitrogen Fertilizer Volatilization. Extension Publication EB0209. Montana State University. http://www.landresources.montana.edu /soilfertility/documents/PDF/pub/UvolBMPEB0209.pdf.

 

– Dr. Jacob Vossenkemper (Agronomy Research Lead)

Tar Spot Update

Summary

Last week Dr. Damon Smith, with the University of Wisconsin, gave an update on Tar Spot and I thought his findings were extremely valuable and the most relevant information I have seen to date.

Tiny black spots against a brown lesion are a symptom of the tar spot complex in corn.

Two corn kernels graphic

Keynotes

- Tar Spot can overwinter and has been in WI for 3 years. It is also in Eastern IA. The first two years Tar Spot was in Wisconsin, it did not infect plants until late August. This year it arrived Mid-June.

- There hasn’t been a single plant found with the Monographella version (the really bad type only found in Mexico so far)

- Tar spot is causing yield loss in the absence of any another disease, such as grey leaf spot.

- Hybrid tolerance incredibly variable. Some can handle it, some take a huge yield hit with this disease.

- Early hybrids take less of a hit. Research is showing that at 10% of the leaf area covered with Tar Spot yields are reduced by 8 bu/ac. Longer maturity (103-113 day) hybrids lost 15 bu/ac when 10% of the leaf area was infected.

- University plant pathologist are creating a phone app (the TarCaster) that will hopefully be able to predict the arrival of the disease based on the weather. They already have a similar program for predicting white mold. They expect that to be out for testing this upcoming year.

- Yield losses appear to be dependent on when the plants become infected with Tar Spot. For example, this year infection started between V8 and VT is some regions but in previous years infection did not start until after milk stage.  There is barely a hit on yield if it arrives during the Milk stage.

-Fungicide does help if timed properly, and at least Headline Amp and Delaro are labeled for Tar Spot.

-University plant pathologist plan on releasing a fungicide update around the end of December to show when the optimum time will be for applying fungicides to control/suppress Tar Spot.