Nitrogen-enhancing biological products provide a level of nitrogen to a corn crop.
Positive yield responses to microbials become more consistent as nitrogen rates fall below plant requirements or environmental nitrogen loss occurs.
Biologicals are a hot topic in agriculture production. The U.S. Farm Bill defines biologicals, or biostimulants, as substances or microorganisms that when applied to seeds, plants or the rhizosphere, stimulate processes to enhance or benefit nutrient uptake, nutrient efficiency, tolerance to abiotic stress or crop quality and yield. Biological products containing bacteria that can fix atmospheric nitrogen (N) and provide plants with plant-available N are a big focus in the agriculture industry.
Figure 1. Trial design with N blocks stripped by biological product and hybrid randomized within those strips at Clinton, ILBiologicals for Nitrogen Management
Many companies have introduced separate biological products that utilize bacteria to form a mutualistic relationship with the plant, resulting in biological nitrogen fixation. The Golden Harvest® Agronomy in Action research team evaluated 3 of these products that are currently on the market at 3 N rates: 100, 140 and 180 lbs. of N/acre. The products include:
- Envita™ – a naturally occurring, food grade bacteria (Gluconacetobacter diazotrophicus) from Azotic North America, applied in-furrow
- Pivot Bio PROVEN® – microbial (Klebsiella variicola) developed by Pivot Bio, applied in-furrow
- BlueN™ – endophytic bacterium (Methylobacterium symbioticum) developed by Symborg, foliar-applied at V4. Recently, Symborg reached a multi-year agreement providing an exclusive distribution license of the bacteria to Corteva Agriscience under the brand name Utrisha™ N.
Each N rate and product was implemented across 3 hybrids at 5 Agronomy in Action locations throughout the Midwest (Figure 1). There was no significant effect between the interaction of hybrid, N rate and product on grain yield, therefore, all results were averaged across hybrid.
Graph 1. Effect of N rate on grain yield averaged across 3 hybrids
* Effect of N rate on yield was significant at α = 0.10. Corn Yield Response to Nitrogen and Biologicals
Clay Center, KS, and Seward, NE, were the only 2 locations where N rate had a significant effect on grain yield and are considered N responsive sites (Graph 1). At Seward, NE, each additional 40 lbs. of N/acre applied resulted in an increase in yield. Statistically at Clay Center, KS, there was no yield advantage when increasing the nitrogen rate from 140 to 180 lbs. of N/acre. The addition of N enhancing biological products did not affect grain yield at the 140 or 180 lbs./acre N rate at any location. Except for Seward, NE, 140 lbs. of N/acre were sufficient to maximize yield, therefore yield responses to biological products that supply plant-available N would not be expected.
The 100 lbs./acre N rate simulates an environment where N loss (from leaching, denitrification, runoff, etc.) may have occurred, resulting in soil N levels below what is required by the plant. In the more N-stressed environment at Seward, NE, applying Pivot Bio PROVEN in-furrow significantly increased yield by 9 bu/A (Graph 2). At Keystone, IA, Envita applied in-furrow resulted in a 27 bu/A yield increase compared to when no biological was applied. There was a 12 bu/A yield response to the foliar application of BlueN at Clay Center, KS. The Clinton, IL, and Slater, IA, plots showed no biological product that significantly increased yield, although, numerically, plants responded positively to Envita at Slater, IA.
Graph 2. Yield response to N-enhancing biologicals at the 100 lbs./acre N rate averaged across 3 hybrids
* Significantly greater compared to no biological at α = 0.10. Basal Stalk Nitrate Test
1 to 3 weeks after black layer, lower stalk samples were collected and analyzed for nitrate levels. Foliar-applied BlueN treatments were excluded due to destructive sampling rows not receiving full application rates.
The basal stalk nitrate test is an end-of-season diagnostic tool that can indicate if N was overapplied. If corn plants have sufficient N available to attain maximum yield for the specific growing conditions, nitrate will accumulate in the lower stalk and increase stalk nitrate levels.
Graph 3. Basal stalk nitrate concentration response to N-enhancing biologicals averaged across 3 hybrids at the 100 lbs./acre N rate
* Significantly greater compared to no biological at α = 0.10. Iowa State University categorizes nitrate concentrations into 3 levels: < 250 ppm = N was likely deficient during the growing season; 250–2,000 ppm = yields were not likely limited by N; and > 2,000 ppm = N was likely overapplied.1
Only at Seward, NE, was the stalk nitrate concentration considered low at the 100 lbs./acre N rate (Graph 3). Neither biological product increased the stalk nitrate concentration to be considered sufficient. Envita and Pivot Bio PROVEN applied at Clay Center, KS, more than doubled the nitrate concentration in the lower stalk compared to when no biological was applied. The increase in concentration did not have a significant impact on yield, suggesting N was not the limiting factor in that environment. Stalk nitrate concentrations tended to slightly increase when Envita and Pivot Bio PROVEN were applied at Clinton, IL, and when Envita was applied Keystone, IL.
Stalk nitrate levels of the untreated check being 1,000 ppm or greater at 4 of 5 locations indicate that other sources of N such as organic matter mineralization contributed significant amounts of N in addition to the 100 lbs./acre N rates. Increases in nitrate levels at Clay Center were negated by sufficient levels in absence of biologicals, resulting in minimal yield increases for both products. However, the increase in nitrates levels does confirm that both products have the ability to influence N availability within the plant.
Biological Technology and Corn Crop Performance
Results from this study aligned with a similar study conducted by the Agronomy in Action team in 2019. Data from both years would suggest nitrogen-enhancing biological products are providing a level of N to the corn crop. However, positive yield responses are inconsistent. Biologicals applied with lower N rates at N responsive locations tend to increase yield potential more consistently. However, there is an inherent risk of yield loss when using microbials to lower synthetic N rates below plant requirements for the given environment.
Biological technology is continuing to advance rapidly. The role of microbials in N management is likely to increase.
References
1 Sawyer, J. and A. Mallarino. 2018. Use of end-of-season corn stalk nitrate test in Iowa corn production. Iowa State University Extension and Outreach. CROP 3154: 1-5.
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