Agronomy Blog

Soybeans – Is there Sulfur in Your Future

by Mark Seem | Feb 15, 2018

Sulfur has long been considered an important consideration for fertilizing a corn crop. In most years 10 pounds per acre of sulfur can show a yield response in corn. And indeed, many researchers are suggesting 20 pounds gives the best response. For soybeans, several studies have historically suggested that a response to sulfur in soybeans is somewhat variable and problematic. However recent research indicates a more positive response to applications of sulfur to soybeans.

Why is sulfur important?
It is a required secondary nutrient for plant growth. Nitrogen, potassium and phosphorus are the primary nutrients. Sulfur, magnesium and calcium are the secondary nutrients. Protein synthesis can’t proceed without sulfur. A component in amino acids, proteins and peptides, many plant functions cannot occur without sulfur. Soybean meal contains the essential amino acids cysteine and methionine which are long chains of sulfur-containing amino acids. Sulfur is also required in the nodulation and nitrogen fixing capabilities of Rhizobia bacteria. Nodules contain high levels of proteins and amino acids. As such, limiting levels of sulfur can limit nitrogen fixation and soybean yield.

Why the concern over sulfur availability?
The sulfur needs of agricultural plants have been met over the years by impurities in fertilizers, sulfur containing pesticides, manure applications, and sulfur provided from the atmosphere resulting from industrial emissions. Sulfur deficiencies have been recognized and becoming a limiting factor in soybean production due to the reduction of sulfur being available from the aforementioned  sources, along with increasing yields that demand higher levels of sulfur, and soil organic levels that are too low to provide enough sulfur.

The chart below, from the EPA, shows the lessoning of sulfur provided by industrial emissions in the past 15 years. It has been estimated that sulfur in rainfall is 10 pounds per acre less than 30 years ago.
sulfur deposition
Current Research
sulfur 2015 field citedDr. Shaun Casteel, Purdue University Extension Soybean Specialist has looked at the response of soybeans to sulfur for several years. His interest in this was peaked after heavy rain events of 2015, and observing the results of rescue treatments of nitrogen and sulfur to water saturated fields.

Results of this study indicated significant positive yield response to applications of both 10 pounds/acre and 20 pounds per acre of Ammonium Sulfate fertilizer (AMS).

This research continued in both 2016 and 2017 and involved broadcast and foliar applications of sulfur along with an untreated check. Results from both years can be illustrated both in the pictures below, and also by the yield advantages reported.

sulfur 2016 pictures2016 Sulfur Responsiveness:

  • Broadcast @ 20 # S/A = +8.5 to 12.5 bpa
  • Single foliar @ 5 # S/A = +6.0 to 10.0 bpa
    • At V4, R2, R4, R6
  • Sequential foliar applications = up to +12 bpa
    • 5 # S/A per application
    • V4 + R2
    • V4 + R4
    • R4 + R6
    • V4 + R2 + R4 + R6

sulfur 2017 pictures2017 Sulfur Responsiveness:

  • Broadcast @ 20 # S/A = +13.0 bpa
  • Single foliar @ 5 # S/A = +4.0 to 7.0 bpa
    • At V4, R2, R4, R6
  • Sequential foliar applications = +5 to 7.5 bpa
    • 5 # S/A per application
    • V4 + R2
    • V4 + R4
    • R4 + R6
    • V4 + R2 + R4 + R6
  • Broadcast application was similar to 2016
  • Foliar applications were not as good as in 2016

In 2017, visual observations of soybean plants and root masses indicated a higher number of nodes, pods and branches on soybeans where added sulfur was applied, along with increased size and numbers of nitrogen fixing nodules on the roots. In addition, aerial images taken by drones clearly showed distinctive differences between plots with added sulfur and those left untreated.

Overall, researchers have seen limited response of soybeans to sulfur. The responses noted here in Indiana may well be the results of cool, wet soils conditions. It has been suggested that soybeans don’t necessarily respond with higher yields, but rather with maintaining higher protein levels. Since the soil organic matter contributes to the background sulfur and nitrogen levels, leaf tissue analysis may be desired, and then apply foliar sulfur once analysis is near .25%, or near a N:S ratio of 18:1.

Much of the information in this technical bulletin is found in a presentation made by Dr. Shaun Casteel at the Indiana CCA conference in December 2017 - https://indianacca.org/media/abstracts/4640_Conference_presentation_(pdf)_1515772574_2017_1213%20Sulfur%20Element%20of%20Surprise%20short.pdf

 

Additional information:
https://www.agprofessional.com/article/does-soybean-crop-need-sulfur
http://msue.anr.msu.edu/news/soybean_response_to_starter_fertilizer_containing_sulfur

https://www.no-tillfarmer.com/articles/4376-questions-to-ask-about-your-soybean-fertility

Note: The information in this issue is based upon field observations and third party information. Since variations in local conditions may affect the information and suggestions contained in this issue, LG Seeds disclaims legal responsibility therefore. Always read and follow label instructions.
LG Seeds and design are trademarks of SCA Limagrain.

Download a copy of this Technical Bulletin: Tech_367 - Soybeans - Is There Sulfur in Your Future