Sulfur plays a part in many plant functions. One of the primary reasons sulfur is critical to crop production is that it works hand-in-hand with nitrogen in the plant. Sulfur is required to allow the plant to use nitrogen efficiently. Sulfur is required for the plant to metabolize nitrogen, which is why poor nitrogen performance in crops is often associated with lower than optimum available sulfur. But sulfur is a vital crop nutrient itself. It is an integral part of amino acids, which are essential for plant protein production. It also contributes to chlorophyll formation which is a key component of photosynthesis in plants.
Why All The Fuss?
Sulfur has always been an important nutrient in crop production. Just as sulfur losses and tie-up have always been a factor in crop production. We have heard more about it in recent years because of the “Clean Air Act” and a variety of environmental stewardship initiatives that have dramatically reduced the amount of sulfur emitted into the air. That sulfur was deposited into the soil to replenish what was lost to crop uptake and the environment. The sulfur available from that source is no longer sufficient to replenish the soil and so we rely on fertilizer sources to supply needed sulfur to plants.
In addition to the loss of atmospheric sulfur, crop yields have increased exponentially over the last 20 years. These high yield goals require a larger supply of all nutrients, including sulfur. Between the increased need for sulfur, the reduced supply of atmospheric sulfur, and losses to the environment, it is necessary to include sulfur as a consideration in all crop nutrition plans.
How It’s Used
While it is considered a secondary nutrient, sulfur (S) is essential to all crops for peak production. Plants use sulfur in the sulfate form (SO4-S), which, like nitrate, is very mobile in the soil and is prone to leaching in wet soil conditions, particularly in sandy soils. Sulfur deficiencies are becoming increasingly common
across North America. About 90% of the sulfur absorbed by plants is found in amino acids, which are the building blocks of proteins. As mentioned earlier, it is essential for chlorophyll formation. It has been shown to increase the synthesis of oils, especially in oil crops such as canola, soybeans, or flax.
Sources of Sulfur
In order to better understand the need for proper sulfur management in crop production it is necessary to understand where sulfur can enter the crop production system and possible avenues of sulfur loss. Sulfur comes from the atmosphere, organic materials such as animal manures and plant residues, and from fertilizers.
Sulfur occurs in many forms, but only sulfate sulfur can be effectively used by plants. Sulfur in any other form needs to be transformed through mineralization or oxidation to become sulfate. That transformation requires the appropriate environmental conditions, biological components and time. As shown on the sulfur cycle diagram, sulfate sulfur can be converted into non-sulfate (and therefore nonavailable) sulfur.
As with all nutrients, sulfur leaves the crop production system through crop harvest, volatilization, runoff or leaching. Of course, it is preferable it be taken up by the crop plant. But sulfur is also susceptible to leaching and volatilization, and can be lost due to runoff and erosion. Those avenues of loss are very similar to nitrogen.
So Now What?
As with almost all crop nutrition planning, the best place to start the discussion on sulfur management is with a soil test. The current methodology for determining sulfur content allows the lab to quantify the amount of sulfate, or SO4 sulfur, as well as sulfur contained in various organic forms. This allows for greater accuracy in determining sulfate sulfur, but it also detects and quantifies forms of sulfur other than sulfate. The reported number includes all forms of sulfur, so the amount listed on the report may not be completely available as sulfate. For example, this method can quantify the amount of sulfur in organic matter (OM), which holds about two to three pounds of sulfur per percentage of OM, but that sulfur is generally in a form that is not available to plants. Remember, the non-sulfate forms of sulfur can be transformed into sulfate, but that requires time and the correct conditions to cause that transformation. Plan that only a portion of the sulfur in that soil test will be immediately available to the plant.
In addition to sulfur’s roles in crop nutrition, it is also a tool that can be used to change the chemical balance in the soil. A proper balance of nutrients in the soil—particularly calcium, magnesium, and potassium, will improve the overall health and productivity of a crop, and improve the ability of the crop to utilize the nutrition that is available to it.
If calcium, magnesium and potassium levels are out of balance, as measured by the base saturation percentage of each nutrient, they need to be brought back into balance in order to provide the best possible growing environment for the crop. Dry soil amendments that contain sulfur can be excellent tools to help rebalance soils that have excess proportions of one or more of those nutrients. Always choose soil amendments according to soil test analysis results. An AgroLiquid agronomist can help in identifying the correct product for a soil amendment. Many AgroLiquid products provide sulfur for crop nutrition, but they are not intended to rebalance the soil’s chemistry.
Feed the Crop
Before we can answer the questions about what AgroLiquid products to use and how much to apply, it is important to determine how much sulfur does the crop need. Sulfur requirements vary depending on the crop and yield goal.
[See below for sulfur removal chart]
Another aspect of sulfur nutrition is to provide enough sulfur to allow for the best nitrogen use efficiency for the crop. The nitrogen to sulfur ratio can help with that determination. In most crops an 8-10:1 nitrogen to sulfur ratio will meet the sulfur nutrition and nitrogen efficiency need.
Among the most versatile sulfur products in the AgroLiquid lineup, eNhance™ can be used as a sulfur source or as a nitrogen performance enhancer. The products accesS® and S-Calate® provide sulfur and sulfur plus calcium nutrition, respectively. Contact an AgroLiquid representative to find out which product will meet your crop needs and goals.
Note that only the amount of each nutrient removed from the grain is reported in this table. When determining total sulfur requirement, consider it in the same way that nitrogen needs are determined, accounting for the sulfur needed for the grain and the stover.
Access and S-Calate are registered trademarks of AgroLiquid. eNhance is a trademark of AgroLiquid. All Rights Reserved.
eNhance is a sulfur product that has a small amount of nitrogen, manganese, and zinc. It can be safely applied in-furrow to many crops as well as a foliar treatment with little risk of crop injury. Common in-furrow use rates are 0.25 – 0.5 gallon per acre, which can provide 3 – 6 lbs sulfur nutrition performance per acre.
The ability of eNhance to be applied in-furrow, 2×2, and as a foliar treatment makes it one of the most versatile sulfur nutrition sources on the market.
AccesS contains 17% sulfur that is readily available to the crop. The formulation keeps the sulfur in an available form and prevents conversion to elemental or organic forms. AccesS can be applied 2×2, broadcast or sidedressed in row crops, top dressed in small grains, and can be applied as a foliar treatment to forage crops such as alfalfa. AccesS should NOT be applied in-furrow or as a foliar treatment to most row crops. While it is commonly mixed with nitrogen products, accesS can be used with many AgroLiquid products.
The third AgroLiquid product that provides sulfur as the principle nutrient is S-Calate. It is a combination of both sulfur and calcium and can be used in much the same way as accesS is used. S-Calate was developed to improve the nutrient efficiency of calcium and sulfur in low pH environments, but it can be used wherever there is a need for both sulfur and calcium.