Alternate forms of nitrogen fertilizer performed similar to urea
A two year study found that the alternate nitrogen (N) fertilizer sources ammonium sulfate nitrate and calcium ammonium nitrate did not perform any better than urea N fertilizer. Treatment with a urease, nitrification or dual inhibitor had few benefits.
A two-year field study assessed the impact of different nitrogen (N) fertilizer formulations on spring wheat production in Alberta. The objectives of this study were to compare alternative granular N fertilizers with urea (46-0-0), and to see if urease and nitrification inhibitors can improve N use efficiencies when banded into the soil. The rational for investigating alternate forms was that they may have fewer volatilization and nitrous oxide losses compared to urea, which would reduce greenhouse gas emissions.
The alternate N fertilizers were ammonium sulfate nitrate and calcium ammonium nitrate. Ammonium sulfate nitrate (ASN) (26-0-0-24) contains both nitrogen and sulfur. The nitrogen is in the ammonium and nitrate forms that is readily available to plants. Calcium ammonium nitrate (CAN) (27-0-0 +8Ca) also contains N in both the ammonium and nitrate forms, and are readily available for crop uptake.
The research was conducted in 2017 and 2018 at Barrhead, AB on a Dark Grey Luvisol soil, and at Lethbridge, AB on a Dark Brown Chernozem irrigated soil.
In the first five treatments, an unfertilized control was compared to the alternative N-based fertilizers of ammonium sulphate nitrate and calcium ammonium nitrate, and these N fertilizers were also applied with and without a nitrification inhibitor (DMPSA). At Barrhead, the fertilizer rate was 89 lbs. N/ac. (100 kg/ha), and these comparisons were on CWRS wheat. At Lethbridge, the fertilizer rate was 36 lbs. N/ac. (40 kg/ha) and the comparisons were on CWAD wheat.
The next four treatments compared untreated urea with urea treated with a nitrification inhibitor (DMPSA), or a urease inhibitor (NBPT), or a dual urease and nitrification inhibitor with the same rates and wheat classes as the first five treatments.
Treatments 10 to 12 compared untreated urea versus urea treated with DMPSA or NBPT on CPSR wheat classes at Barrhead at 89 lbs. N/ac., and CWAD at Lethbridge at 80 lbs. N/ac.
At Barrhead, all N fertilizer treatments were mid-row banded three inches deep. Fertilizer N at the irrigated Lethbridge site was also mid-row banded but at a slightly shallower depth of 2.75 inches.
In addition to the N fertilizer treatments, all treatments received 17.8 lbs P2O5/ac (20 kg P2O5/ha) in the seed row and 17.8 lbs P2O5/ac + 13.4 lbs K2O/ac (15 kg K2O/ha) in the mid-row band. Herbicide and fungicide applications were applied as needed.
Few differences between formulations and inhibitor treatments
Shoot nutrient uptake of N was generally very similar across treatments, with few differences between fertilizer sources, urease and nitrification inhibitors, and wheat classes. The exceptions were lower N uptake in the unfertilized control, and higher N uptake in durum wheat at the 80 lbs. N fertilizer rate. Total plant N uptake in shoot and grain N content was similar across treatments and soil types.
Averaged across wheat class and site years, there were no significant yield differences between untreated urea, ASN and CAN fertilizers. Yield ranged from 77.0 bu./ac. (5171 kg/ha) for CAN to 77.6 bu./ac. (5209 kg/ha) for urea. However, untreated urea and urea plus a nitrification inhibitor had significantly higher yield than urea plus a urease inhibitor, although the yield difference was less than two bu./ac.
For grain protein content, urea had the highest protein content at 12.3% but was statistically similar to ASN that was intermediate at 12% and CAN the lowest at 11.7%.
The researchers say that a lack of differences for most treatments, excluding the unfertilized controls, was due to deep banding of the fertilizer N. Banding can reduce volatilization and nitrate-N losses, especially under the tested conditions, leading to urea and the alternate fertilizers performing similarly.
Additionally, since there were only minor yield differences between sources, with or without inhibitors, there is little incentive to switch N source away from un-stabilized urea when deep banding is the preferred method of fertilizer placement. The alternate products, ASN and CAN also contain 60% of the N content of urea, which would result in the application of increased product volume compared to urea. This means increased transportation, storage and application costs.
The alternative sources, which are nitrate-N based (NO3–), also have greater potential for soil acidification than urea.
Overall, the researchers concluded that “the findings of this study reinforce the continual use of urea as a banded N source for spring wheat production within the Canadian prairies and provides little evidence towards the use of alternative nitrogen-based formulations tested under these conditions. In their un-stabilized states, urea performed marginally better in the Dark Grey Luvisol soil, while slight improvements observed in the alternative formulations (i.e., ASN and CAN) occurred within the Dark Brown Chernozem due to possible downward soil profile movement of nitrate.”
This study was funded in partnership with the Government of Alberta, Agriculture and Forestry division and the University of Alberta.
Dr. Kris G Guenette, Dr. Guillermo Hernandez-Ramirez, and Dr. Sheri Strydhorst. The influence of nitrogen source and stabilization in fertilizer formulations on Western Canadian spring wheat. Canadian Journal of Soil Science. OPEN ACCESS https://doi.org/10.1139/cjss-2024-0118
