Does sulphur Pay?

Monday, December 30, 2024

Can you make more bushels with it in your soybean crop?

By Paul Hermans

An agronomist would answer the title question with “It depends!”

Over the past decade, a lot of focus has been put on sulphur, and rightly so. Since the late 1980s, governments and industries across North America have done an excellent job of reducing air pollution. This has reduced acid rain and other depositions, including sulphur.

In the past, we received enough sulphur from these depositions for crop growth on an annual basis. The question remains: What does a grower need to do to ensure they have enough sulphur in their crops?

In this article, I will review what sulphur does in the plant, types of fertilizer, and some local research we did in 2023 and 2017 – along with some management tips you can look at for next year’s cropping season.

Role in the plant

Sulphur is an essential nutrient in crop production and is ranked fourth in importance behind the big three: Nitrogen, phosphorus, and potassium. It is a major component of amino acids that assists with plant protein synthesis. About 95 per cent of our sulphur comes from organic matter. In livestock operations, manure can be an important source of sulphur. Sulphur can be mineralized in the soil. This occurs with warm, moist soils. This is partially the reason we see more of a response to sulphur on earlier planted soybeans than later planted soybeans.

In soybeans, it has been linked to enhancing nodulation and the overall nitrogen uptake of a soybean crop. Like nitrogen, sulphur can also be leached in the soil – another reason we tend to see higher yield responses on sandier soils than loam/clay soils.

There are differences in crop uptake and responses to sulphur. Wheat and alfalfa respond to sulphur. Other crops like corn and soybeans are not as responsive under all general conditions but respond to certain soil types and management practices.

Sulphur types

There are various forms of sulphur fertilizer. Sulphate-containing fertilizers provide sulphur in a form that is readily available for plant uptake and can be used to quickly correct a sulphur deficiency. Conversely, elemental sulphur must be oxidized in the soil before it can be taken up by plants. This increases the time needed for it to be made available, but it is a slow-release form that is less susceptible to leaching losses than sulphate fertilizers.

Ontario research

So why all the buzz around sulphur in soybeans?

In 2023, Shaun Casteel, a researcher from Purdue University, showed big yield gains on his research work when sulphur was applied, versus untreated checks. The biggest gains occurred in his research work in early planted soybeans.

To answer the question “Would it pay in soybeans?” we conducted some yield trial work in East/Central Ontario looking at sulphur on soybeans. Twelve field locations were picked, with two replications per site. Each replication treatment was an acre in size. Sulphur treatments consisted of urea (46-0-0) at 100 pounds to the acre + ammonium sulphate (21-0-0-24) at 40 pounds to the acre. All treatments were applied prior to planting and worked into the soil profile.

Overall, there was no response to sulphur applied. When we looked at planting date trials planted before May 10, there was a 1.2-bushel response. Trials planted after May 10 were 0.8 bushels less. This supports the theory that sulphur is more readily available (mineralized) under warmer conditions, and crops respond more to applications earlier in the season than later.

In 2017, we also conducted a soybean sulphur trial to look at specific soil types. Among trial locations with sandy soil, the addition of sulphur fertilizer increased yields by 4.1 bushels per acre. No yield response was observed with loam soils.

You may be asking yourself why there is a difference in the Purdue University work compared to Ontario. A lot would come down to soil type differences, organic matter differences and sulphur availability at planting time. Hence the reason to evaluate theories that look good in other areas and make sure they work at home.

So, what does a grower do moving forward?

Look at using sulphur, especially in higher-use crops like wheat and alfalfa.

As soybean yield continues to increase, crop removal will increase as well. This may warrant the addition of sulphur in your crop fertility program.

Target specific lower organic matter and lower texture soils for soybean response.

Earlier planted soybeans will respond more to sulphur than later planted.

Conduct replicated trials on your farm to see if yield advantages exist with your management practices. BF