Soybeans Need for Supplemental Nitrogen

• In high-yielding environments with conditions conducive to nitrogen loss, the potential for soybean yield response to nitrogen (N) is greatest.
• Biologicals could have potential to supplement N in soybeans without reducing nodulation and N fixation.

Soybeans have a high demand for nitrogen (N) and must accumulate 4.8 lbs. of N per bushel. It has been documented that biological N fixation from Bradyrhizobium can supply roughly 60% of the N requirement for soybeans.¹ The other 40% must come from the soil through mineralization or synthetic N fertilizers. At low yield levels, it is likely the soil can supply the remaining N requirement for soybeans. However, in high-yield environments the soil may not be able to mineralize enough incremental N above what is supplied by Bradyrhizobium to meet the total demand of soybeans.

The presence of plant-available N (nitrate or ammonium) has been shown to reduce nodule formation, growth and activity in soybeans.^2,3,4 The reduction is directly proportional to the soil level of N supply so applications of synthetic N fertilizers may not be an effective method to fill the N requirement gap. A slow-release form of N through biological fixation from other bacteria could be a promising concept to meet this need. Alternatively, synthetic N fertilizer applied later in the season, after peak nodulation has occurred, may be a way to provide N without reducing nodulation.

Agronomy in Action Trials

The Golden Harvest^® Agronomy in Action research team implemented trials at 8 locations across the Midwest designed to supplement N to soybeans without reducing nodulation. 2 different Golden Harvest soybean varieties, either GH2102XF and GH2329X, or GH2788X and GH3088X, or GH3475X and GH3546X, were grown at each location.

3 biological products were evaluated, including BlueN™, Envita™ and New Tech SI-IF™. BlueN is an endophytic bacterium (Methylobacterium symbioticum) developed by Symborg that is foliar-applied at the V4 growth stage. Recently, Symborg reached a multi-year agreement providing an exclusive distribution license of the bacteria to Corteva Agriscience under the brand name Utrisha™ N. Envita is a naturally occurring bacteria (Gluconacetobacter diazotrophicus) from Azotic North America that is applied in-furrow or foliar at the V4 growth stage. New Tech SI-IF from TerraMax is a soybean inoculant (Bradyrhizobium japonicum) combined with a bacteria known to fix N and enhance root hair growth and development (Azospirillum brasilense) that is applied in-furrow.

In addition, 3 synthetic N fertilizer treatments were included in the trial. Either 30, 60 or 90 lbs. of N/acre was broadcasted as Agrotain^®-coated urea at the R3 growth stage. The R3 growth stage is beyond peak nodulation, minimizing the negative effect of soil nitrate concentration on nodulation.

Nitrogen Management Effect on Soybean Yield  

On average, across all locations and varieties, there was little yield difference between the biological or synthetic N treatments compared to the check (Graph 2). New Tech SI-IF was the highest yielding treatment averaging 73.6 bu/A. Any potential yield responses to the different rates of synthetic N may have been mitigated by leaf burn from the broadcast Agrotain^®

Clinton and Elwood, IL, experienced environmental conditions that were conducive for soybean N limitations. Both locations were high yielding, with Clinton averaging 91 bu/A and Elwood yielding 77 bu/A. At those yield levels, the crop would require 437 and 370 lbs. of N/acre, respectively. If N fixation supplies 60% of the plant N requirement, the remaining N gap that would need to be supplied from the soil would be 175 lbs. of N/acre at Clinton and 148 lbs. of N/acre at Elwood. Clinton received nearly 8 in. of precipitation in June and Elwood received 7 in., which is close to double the 30-year average during June at both locations. Nitrogen loss through leaching was likely during this time.

Tech SI-IF significantly increased yield by 5.1 bu/A at Elwood and numerically by 2.0 bu/A at Clinton compared to the check (Table 1). Soybeans tended to respond by 1.6 bu/A when Envita was applied either in-furrow or with a foliar application at V4 in Elwood. BlueN also tended to provide a 2.4 bu/A yield increase at Elwood. The 60 lbs./A of N rate significantly increased yields at Clinton. At Elwood, all rates of synthetic N fertilizer tended to increase yield with the response being greatest at the 30 lbs./A of N rate. This rate likely supplemented N with minimum leaf burn compared to the higher rates.

In these high-yield environments that were subject to N loss, the slow-release form of N through biological fixation from bacteria likely supplemented the N requirement for soybeans and reduced the N demand gap.

Effect on Nodulation

Roots from plants in the border rows of the check, Envita and New Tech SI-IF in-furrow treatment plots were evaluated for nodulation at the R2 growth stage. The degree of nodulation was rated on a scale from 0-3. A score of 0 would mean no nodules were present. Nodules present on only the taproot would be a score of 1. A score of 2 would have nodules present on the taproot and 1-3 lateral roots while a score of 3 would mean nodules were present on the taproot along with 4 or more lateral roots. Nodules were removed from the roots and split open, and the percentage of nodules that were pink, or healthy and active, on the inside was recorded.

There was no effect of either biological application on nodulation or nodule activity at any location. These results indicate that N fixed from the bacteria in these products does not reduce nodulation. Also, any yield responses from New Tech SI-IF were likely driven by N fixed from the Azospirillum brasilense bacteria and potentially increased root hair development, rather than the Bradyrhizobium japonicum increasing nodulation.

Summary

Results from this study show that soybean response to synthetic N fertilizer and N-enhancing biologicals are inconsistent and environment dependent. Many factors contribute to the potential of soybean yield to be limited by N. In high-yielding environments with conditions conducive to N loss, the potential for soybean yield response to N is greatest.

To learn more about strategies to reduce nitrogen limitations in soybeans, watch this video.

References

¹ Salvagiotti, F., Cassman, K. G., Specht, J. E., Walters, D. T., Weiss, A., and Dobermann, A. 2008. Nitrogen uptake, fixation and response to fertilizer N in soybeans: A review. Field Crops Research. 108(1), 1-13.

² Gardner, F. P., Pearce R. B., and Mitchell R. L. 1985. Physiology of crop plants. Iowa State Univ. Press, Ames.

³ Herridge, D. F. 1984. Effects of nitrate and plant development on the abundance of nitrogenous solutes in root-bleeding and vacuum-extracted exudates of soybean. Crop Science. 24(1), 173-179.

⁴ Hungria, M., Franchini, J. C., Campo, R. J. and Graham, P. H. 2005. The importance of nitrogen fixation to soybean cropping in South America. Nitrogen fixation in agriculture, forestry, ecology, and the environment. Springer, Netherlands. 25-42.

All photos are either the property of Syngenta or used with permission.

Syngenta hereby disclaims any liability for Third Party websites referenced herein.

Performance assessments are based upon results or analysis of public information, field observations and/or internal Syngenta evaluations.

Product performance assumes disease presence.

© 2022 Syngenta. Important: Always read and follow label instructions. Some products may not be registered for sale or use in all states or counties. Please check with your local extension service to ensure registration status. AAtrex 4L, AAtrex Nine-O, Acuron, Agri-Flex, Agri-Mek 0.15EC, Agri-Mek SC, Avicta 500FS, Avicta Complete Beans 500, Avicta Complete Corn 250, Avicta Duo Corn, Avicta Duo 250 Corn, Avicta Duo COT202, Avicta Duo Cotton, Besiege, Bicep II Magnum, Bicep II Magnum FC, Bicep Lite II Magnum, Callisto Xtra, Cyclone SL 2.0, Denim, Endigo ZC, Endigo ZCX, Epi-Mek 0.15EC, Expert, Force, Force 3G, Force CS, Force 6.5G, Force Evo, Gramoxone SL, Gramoxone SL 2.0, Gramoxone SL 3.0, Karate, Karate with Zeon Technology, Lamcap, Lamcap II, Lamdec, Lexar EZ, Lumax EZ, Medal II ATZ, Minecto Pro, Proclaim, Tavium Plus VaporGrip Technology, Voliam Xpress and Warrior II with Zeon Technology are Restricted Use Pesticides.

Some seed treatment offers are separately registered products applied to the seed as a combined slurry. Always read individual product labels and treater instructions before combining and applying component products.

Orondis Gold may be sold as a formulated premix or as a combination of separately registered products: Orondis Gold 200 and Orondis Gold.

Important: Always read and follow label and bag tag instructions; only those labeled as tolerant to glufosinate may be sprayed with glufosinate ammonium-based herbicides. LibertyLink^®, Liberty^® and the Water Droplet logo are registered trademarks of BASF. HERCULEX^® and the HERCULEX Shield are trademarks of Corteva Agriscience LLC. HERCULEX Insect Protection technology by Corteva Agriscience LLC. Under federal and local laws, only dicamba-containing herbicides registered for use on dicamba-tolerant varieties may be applied. See product labels for details and tank mix partners. Golden Harvest^® and NK^® soybean varieties are protected under granted or pending U.S. variety patents and other intellectual property rights, regardless of the trait(s) within the seed. The Enlist E3^® soybean, LibertyLink^®, LibertyLink^® GT27^®, Roundup Ready 2 Xtend^®, Roundup Ready 2 Yield^® and XtendFlex^® soybean traits may be protected under numerous United States patents. It is unlawful to save soybeans containing these traits for planting or transfer to others for use as a planting seed. Only dicamba formulations that employ VaporGrip^® Technology are approved for use with Roundup Ready 2 Xtend^® and XtendFlex^® soybeans. Only 2,4-D choline formulations with Colex-D^® Technology are approved for use with Enlist E3^® soybeans. The trademarks or service marks displayed or otherwise used herein are the property of a Syngenta Group Company. ENLIST E3^® soybean technology is jointly developed with Corteva Agriscience LLC and M.S. Technologies, L.L.C. The ENLIST trait and ENLIST Weed Control System are technologies owned and developed by Corteva Agriscience LLC. ENLIST^® and ENLIST E3^® are trademarks of Corteva Agriscience LLC. GT27^® is a trademark of M.S. Technologies, L.L.C. and BASF. Roundup Ready 2 Xtend^® , Roundup Ready 2 Yield^®, XtendFlex^®, VaporGrip^® and YieldGard VT Pro^® are registered trademarks used under license from the Bayer Group.

All other trademarks are the property of their respective owners. More information about Agrisure Duracade^® is available at http://www.biotradestatus.com/.