Using Biologicals as a Component of Fertility Management in Soybeans

• Scientific advancements in biological development will continue to push the possibility of yield increases. 
• When resources such as sunlight, nutrients and water are sufficient, there will be less opportunity for benefits from biologicals. 

In recent years, using biologicals – plant protection products derived from living organisms – in crop production has been a focus of attention. Scientific advancements in gene editing, along with the reduction in cost of genome sequencing, has resulted in large investments in biological research and development. The potential to help farmers produce higher yields while simultaneously promoting environmental sustainability is driving the interest in biologicals. Soil microorganisms provide many important agronomic benefits to crops, such as: 

• Fixing atmospheric nitrogen 
• Converting soil nutrients not available for plant use into plant-available forms 
• Creating symbiotic relationships with plants 
• Producing plant growth regulators that can stimulate root growth 
• Competing against plant pathogenic fungi, parasites and other pests 
• Potential Benefit of Biologicals in Soybean Production 

Soybeans have a high demand for nitrogen (N) and must accumulate 4.8 lbs of N per bushel. It has been documented that biological nitrogen fixation from Bradyrhizobium can supply roughly 60% of the nitrogen requirement for soybeans.⁴ The other 40% must come from the soil through mineralization or synthetic nitrogen fertilizers. At low yield levels, it is likely the soil can supply the rest of the required nitrogen for soybeans. However, as yield levels increase, the soil cannot mineralize enough nitrogen to meet the nitrogen demand of soybeans that is not supplied by biological nitrogen fixation from Bradyrhizobium. 

The presence of plant-available nitrogen (nitrate or ammonium) has been shown to reduce nodule formation, growth and activity in soybeans.^1,2,3 The reduction is directly proportional to the soil level of N supply, so applications of synthetic nitrogen fertilizers may not be an effective method to fill the nitrogen requirement gap in soybeans. A slow release form of nitrogen through biological fixation from other bacteria could be a promising concept to meet this need. Biologicals that can stimulate root growth, improve nutrient uptake and reduce plant stress may also help overcome nutrient deficiencies often seen in soybean production. 

Agronomy in Action Trials
In 2020 Golden Harvest® Agronomy in Action research trials, 2 biological products were evaluated at 8 locations across the Midwest (Figure 1). 

Envita®, introduced by Azotic North America, utilizes a naturally occurring bacteria (Gluconacetobacter diazotrophicus) to form a beneficial relationship with the plant and fix atmospheric nitrogen within every plant cell.  

Terrasym® 401, a seed treatment for soybeans that includes beneficial microbes called methylobacterium (M-trophs), was developed by NewLeaf Symbiotics. NewLeaf Symbiotics claims that the bacteria form a symbiotic relationship with the plant that improves plant development, nutrient uptake and tolerance to abiotic stresses. 

Field research locations were managed according to the normal practices for the local grower. Envita was applied in-furrow at planting while Terrasym 401 was applied as a seed treatment. 

The Golden Harvest soybean variety, precipitation amount and soil test values for each location are outlined in Table 1. All soil test levels for phosphorus (P) were adequate or above adequate for all locations except Bridgewater, SD, Clay Center, KS, and Seward, NE. Soils at Bridgewater and Cedar Rapids, IA, had borderline adequate potassium (K) levels, and Slater, IA, was below adequate. The lowest organic matter soils were at Clay Center, Seward and Storm Lake, IA. 



Trial Results 
Yield environments were significantly different across locations with averages ranging from 53 bu/A at Bridgewater to 104 bu/A at Seward. When averaged across all locations, there was no yield difference between the check and the application of either biological product. At individual locations, grain yield responses to biological treatments were inconsistent. Soybeans grown at Bridgewater and Slater experienced the highest positive yield response when Envita was applied in-furrow, yielding 3.9 and 3.2 bu/A greater than the check, respectively (Graph 1). The only location where applying Terrasym 401 as a seed treatment tended to increase yield over the check was at Slater, yielding 6.5 bu/A greater (Graph 2).  

 
Conclusion
Yield is complex, and yield responses to biological treatments may be year and environment dependent. There are many moving parts that need to fall into place to see a yield increase from biological products. These products contain live bacteria which must stay alive through the application process and continue to live in the soil. The bacteria also need to colonize the plant in order to form a symbiotic relationship and ultimately provide benefits. Finally, the yield potential of the plant must be limited without the benefits provided by the bacteria. For example, if a soybean plant is not nitrogen deficient, then applying a biological product that provides nitrogen to the plant will likely not increase yield. More research efforts to understand these environmental interactions with biological products are needed. 

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

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