Does Manure Have a Place in the Sulphur Debate?

Sulphur is considered a secondary element, along with calcium and magnesium. Sulphur is required in moderate amounts by plants, but is less likely to limit crop growth than nitrogen, phosphorus or potassium. There has been renewed debate about sulphur requirements for crop production in Ontario, due to the reduction of sulphur deposits through acid rain. Where does manure fit into that debate?

Manure and biosolids contain sulphur. The process of sulphur availability is similar to the process of nitrogen availability from manure. Manure contains sulphur in both organic and inorganic forms. A portion of the sulphur in manure will be readily available as sulphate (SO₄²). The other portion that exists as organic sulphur must be converted (mineralized) to sulphate by soil microorganisms before it can be utilized by plants. Most of the sulphur in the soil is in the organic matter. 

Source: Pennsylvania State University
SO₂ = sulphur dioxide
SO₄^2- = sulphate

Sulphur content in manure varies similar to other nutrients, based on livestock type, manure type (liquid vs. solid), bedding type and ration. There is limited analysis data for sulphur in Ontario. Early estimates from a small sample size suggest that in most manure types 25 to 30 percent of the total sulphur is readily available as sulphate. For poultry manures almost all the sulphur is in sulphate form, and early estimates reveal 5 lbs per ton.

Information collected from the USA (American Society of Agronomy Crop Science and Soil Science) and shown in Table 1 estimates the total and available sulphur content from different livestock types.

Table 1. Estimate of Available Sulphur from Manure by Animal and Manure Type

There is variation in the amount of sulphur found in manure depending on livestock type, application rate and frequency of application. The debate of sulphur needs for Ontario crops will continue with interest while awaiting side-by-side plot results. However, fields that are manured on a regular basis, with good organic matter levels will not be likely candidates for sulphur deficiency. 

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