When deciding on what phosphorus source is best for your crop, companies may refer to the type of acid used in their phosphorus starter. You’ll likely hear one of these terms:
- Black Acid - it’s black because there is carbon in it.
- Green Acid - which is green or sometimes translucent, has some carbon in it.
- White Acid - which has been conditioned to remove the carbon, has no carbon. The conditioning typically will mean the product has been handled more and therefore often costs more. White acid does typically have a higher ratio of ortho to poly phosphates.
Field Study
Dr. Jake Vossenkemper completed trial work locally to prove this and has provided a 5-site year summary below.
for In-Furrow Seed Safe Starter Fertilizers – 5 Site-Year Summary
What Dr. Jake found was, 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.
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.
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.
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
