Elemental Sulfur: A Nitrogen Fixing Helper for Legumes
How elemental sulfur helps your legume crops fix nitrogen in the soil
Elemental Sulfur has many benefits to enhance your soil for optimum plant growth.
One of the lesser known, yet quietly powerful of these advantages, is its ability to help your legume crops fix nitrogen in the soil.
Here’s a look at how this works:
Advantages of legumes
Legumes are a family of plants that produce seed-bearing pods that are a nutritious food source. Common examples include beans, soybeans, chickpeas, lentils, peas, alfalfa, and more.
Legumes have grown in popularity for use in crop rotations, in part due to their unique capability to help replenish nitrogen (N) in the soil.
Legumes provide a symbiotic “home” for rhizobia bacteria, which are one of nature’s nitrogen producers. The nitrogen these bacteria produce benefits the legume crops themselves, as well as the next crops in the rotation.
This results in less need for (and cost of ) N fertilizer along with improved crop results, providing farmers with an outstanding economic strategy for boosting success both in the short and longer term.
But did you know that legumes rely heavily on sulfur to facilitate nitrogen fixation?
Here’s a breakdown of how this works and how Elemental Sulfur specifically is an excellent tool to optimize the N fixation activity of legumes:
How legumes fix nitrogen
The ability of legumes to fix nitrogen is based on the symbiotic relationship of these plants with the rhizobia bacteria present in the soil.
Rhizobia bacteria are a special form of bacteria that can stimulate the growth of nodules in the roots of legume plants.
These bacteria are also natural “nitrogen-fixing bacteria” – they can take N from the air or environment, break it down, and combine it with oxygen or hydrogen into compounds such as ammonia that are soil-enhancing and available for plants to use for growth.
This transformation of N from the air or environment into ammonia is known as “nitrogen fixing.”
The power of symbiosis
Legumes support N fixing because they provide an excellent home for the rhizobia bacteria to thrive. Specifically, the rhizobia bacteria are incorporated into the root nodules of the legume plants, and in these special protective houses, they work anaerobically to fix N into ammonia, using an enzyme called nitrous, which combines oxygen or hydrogen with nitrogen.
The resulting ammonia is readily absorbed by plants and used to manufacture amino acids, proteins, nucleic acids, and other nitrogen-containing components – all in support of healthy and robust plant growth.
Some of this ammonia is used by the legume plants themselves, but there is typically far more created than the legumes can use, which stays in the soil and is available to the following crops in the rotation.
In addition to receiving a protective home from the legume plants, rhizobia bacteria also receive a healthy dose of photosynthate from the legumes. Photosynthates are sugars produced by photosynthesis – they help feed and fuel the further growth of the rhizobia bacteria population.
This makes for a true “win-win” symbiotic relationship.
Producing results: How sulfur is “in on the fix”
The results are very substantial. In legumes, this relationship can produce an impressive 25-75 lb of nitrogen per acre per year in a natural ecosystem – and several hundred pounds in a cropping system.
Sulfur is an important factor in these impressive numbers, because nodulated legumes are known to have a high sulfur demand, and there is a direct correlation between sulfur availability and nitrogen fixation. For example, to grow a 60-bushel soybean crop requires approximately 30 lb of S.
Sulfur plays an important role in nitrogen fixation, particularly in the following areas:
Promotes the formation of nodules. Pulse crops suffering from sulfur deficiency have fewer and smaller nodules. Sulfur-deficient nodules contain less leghemoglobin (in the cytosol), glucose, and ATP (adenosine triphosphate, a molecule that provides energy to the plant).
Supports symbiotic nitrogen fixation. Sulfur is a key ingredient in nitrogenase. Nodules in sulfur-deficient plants will suffer from lower rates of nitrogenase biosynthesis: thus limiting the conversion of nitrogen (N2) to plant-available nitrate (NO3). Sulfur is also a key component of numerous enzymes, including ferredoxin (an iron-sulfur compound essential to photosynthesis and nitrogen fixation). Ferredoxin helps the rhizobium assimilate nitrogen.
Enhances nodule metabolism. Sulfur also plays an important role in the uptake/transportation of nutrients and enzymes. It is necessary for the formation of proteins and chlorophyll, facilitating the plant’s ability to efficiently use nitrogen.
Why elemental sulfur is a great choice to support N fixing
Elemental sulfur is an excellent option to help ensure your legume crop has the support it needs to maximize N fixation, particularly when using a high-quality bentonite elemental sulfur such as our Keg River products. This is due to the unique slow-release, season-long benefits of bentonite elemental sulfur, which results in steady support for the legume crop throughout the growing season.
To get your Elemental Sulfur strategy right, before you seed a legume crop, it is advisable to soil test for sulfur levels to avoid the risk of deficiency.
You will want to ensure your Elemental Sulfur strategy supports an immediate and ongoing source of sulfur when growing your legumes, so you don’t lose out on all that valuable natural N-fixing capability – along with the associated cost savings and environmental benefits that come with it.
Read more about Why Sulfur is Necessary for Nitrogen Fixation in Legumes.
