FACTORS AFFECTING SULFUR MINERALIZATION
Sulfur content of organic matter
Mineralization of sulfur depends on the sulfur content of the decomposing material in much the same way that nitrogen mineralization depends on the nitrogen content. Smaller amounts of S042- are liberated from low sulfur containing residue, which is similar to nitrogen mineralization. At or below a C/S ratio of approximately 200/1 only mineralization of sulfur occurs.
Source of mineralizable sulfur
Because of the contribution of sulfur mineralization to plant-available SO42-, there is interest in characterizing the labile sulfur reserve in soil organic matter. Most of the available sulfur removed by plants probably comes from the ester SO42- fraction although other organic sulfur compounds are also involved.
Mineralization of sulfur is severely impeded at 10°C, increases with increasing temperatures from 20° to 40, and decreases at temperatures >40°C.This temperature effect on sulfur mineralization is consistent with the relatively greater sulfur content of soils formed in northern climates.
Mineralization of sulfur in soils incubated at low (40%) moisture levels is reduced compared to the content of 60% of field moisture-holding capacity. Gradual moisture changes in the range between field capacity and wilting point have little influence on S mineralization. However, drastic differences in soil moisture conditions can produce a flush of sulfur mineralization in some soils. Increased availability of sulfur due to soil wetting and drying may explain the observations of increased plant growth after dry periods in sulfur deficient soils.
The effect of pH on sulfur mineralization is not clear. In soils from other regions, the amount of sulfur released is directly proportional to pH up to a value of 7.5. At pH values above 7.5 in these soils, mineralization increases more rapidly suggesting that an additional...