Potential of Biologicals for Nitrogen Management

• Microbial products are now available that utilize bacteria to form mutualistic relationships with plants, resulting in biological nitrogen fixation. 
• Field trials show promise for biologicals to increase yield potential, although yield response may not always be observed.  
• Yield responses from microbials will be more likely if nitrogen application rates are less than plant requirements or environmental nitrogen loss occurs through leaching, denitrification, runoff, etc.  

Nitrogen management is one of the most complex issues farmers deal with on a year-to-year basis. The economically optimal nitrogen rate depends on yield potential, soil type, previous crop, form of nitrogen, timing of application and weather, among other things. Rainfall, for example, can influence both the application timing and extent of soil nitrogen loss after application. Traditionally, monitoring in-season soil nitrogen availability and adding supplemental nitrogen as needed have been key elements for managing the complex soil nitrogen cycle. Newly introduced biological in-furrow and seed treatment products provide new options for managing risk of nitrogen loss as well as a potential method to reduce overall nitrogen rates.

Biologicals for Nitrogen Management 
2 companies recently introduced biological products that utilize bacteria to form a mutualistic relationship with the plant, resulting in biological nitrogen fixation. Azotic North America introduced Envita™, a naturally occurring, food-grade bacteria (Gluconacetobacter diazotrophicus). Pivot Bio introduced a microbial product called Pivot Bio PROVEN®. Although both products use biological nitrogen fixation to deliver nitrogen to the plant throughout the growing season, they utilize entirely different bacteria to do so. 

Pivot Bio PROVEN is a microbial product that is applied in-furrow at planting. Microbes attach to the outside of developing roots and colonize throughout the growing season. The bacteria then take in nitrogen from the air and produce plant-available ammonia within the roots that is redistributed throughout the plant.  

Envita works slightly differently. Their bacteria can be found colonizing both in the roots as well as above ground within individual chloroplast, helping to produce additional chlorophyll in plant leaves. Azotic claims growers can reduce total synthetic nitrogen applied in season due to Envita’s ability to replace 27% of the total nitrogen needed by a corn plant on average. They also claim using Envita in addition to a standard nitrogen fertility program can result in 5-13% corn yield increases.

Pivot Bio states that Pivot Bio PROVEN delivers the equivalent of 25 lbs of synthetic nitrogen per acre. Some of their customers reduce commercial fertilizer rates when using Pivot Bio PROVEN, although the company recommends maintaining normal nitrogen rates and adding Pivot Bio PROVEN to improve nutrient efficiency. The potential value of application simplicity, reduced risk of yield loss from nitrogen unavailability and improved environmental sustainability have created interest in the performance of both products.

2020 Nitrogen Biological Evaluations 
Golden Harvest® Agronomy in Action research trials were established at 8 locations in 2020 to better understand potential value of these biological products’ ability to provide nitrogen and enhance yield. 2 of 8 locations were lost to the late season derecho wind events, so results focus on the 6 remaining sites (Figure 1). A uniform rate of nitrogen was determined for each location based on local grower application rates, and nitrogen was applied uniformly prior to planting (Table 1).

Pivot Bio PROVEN and Envita were separately applied as in-furrow treatments at the time of planting using a specialized research application system (Figures 2 and 3) to avoid plot-to-plot contamination. Comparison plots not receiving any biological additives or additional nitrogen were also planted simultaneously and replicated 4 times per location. Biological products remained sealed in their original container until 48 hours in advance of planting to ensure microbial activity was not impacted.
 

Summary and Discussion 
Yield environments were significantly different across the 6 trials conducted in the 2020 crop season, ranging from 173 bu/A at Sac City, IA, to 278 bu/A at Seward, NE. Across sites, yields corresponded to differences in plant-available water such as rainfall and irrigation. Overall, lower-than-normal rainfall across locations helped to minimize potential loss of nitrogen. For example, the Sac City, IA, site received roughly 68% of the normal April-August 10-year precipitation average. Nitrogen recommendations estimated by Adapt-N on July 1 for each location showed that most locations had sufficient nitrogen to meet crop demand. Only 2 locations, Seward, NE, and Clinton, IL, had recommendations to apply additional nitrogen to meet current yield goals.

Statistically, no yield response was observed for either microbial product at any location, although Seward and Clinton did have a numerical increase (Graph 1). These are the same 2 locations that Adapt-N called for incremental nitrogen applications. There were 9.9 and 2.5 bu/A responses from Pivot Bio PROVEN and Envita, respectively, at Seward. There were 5.9 and 4.3 bu/A responses from Pivot Bio PROVEN and Envita, respectively, at the Clinton location. There was also a 1.5 bu/A response to Envita at the Oregon, IL, location. Although not statistically significant, equivalent or reduced yields at the remainder of the locations resulted in a net loss for covering the cost of products applied. Retail price of Pivot Bio PROVEN ($20/A) and Envita ($9.95/A) and a corn price of $3.80/bu were used to look at the return on investment for locations with positive yield responses. Pivot Bio PROVEN netted a $2.57/A return in Clinton and a $17.73/A return in Seward. Yield response of Envita was only great enough at the Clinton location to provide a return on investment ($6.31/A). 

Conclusion
The concept of utilizing microbial products to help plants reduce their need for synthetic nitrogen is very promising as an additional tool to help manage nitrogen. However, it also potentially adds an additional layer of complexity when trying to determine the right rate, placement and timing. There is an inherit risk of yield loss when using microbials to lower synthetic nitrogen application rates if the amount of nitrogen that the microbials provide is not known or consistently observed. There is an additional risk of financial loss if yield increase is not significant enough to offset the cost of applying microbials.

We know from many trials that the yield response to nitrogen does eventually plateau when adequate nitrogen is available (Graph 2). Due to this, there is a point at which there should be no anticipated yield response from microbials until nitrogen rates are reduced or environmental nitrogen loss from leaching, denitrification or runoff occurs.  

For more information on nitrogen management, contact your local Golden Harvest Seed Advisor.