Lecture 13- Soil Sulphur

Vocabulary flashcards covering soil sulphur dynamics, deficiency factors, transformations, fertilizers, and buffering capacity based on the lecture module.

Prairie Soil Sulphur Deficiency

The reduced availability of sulphur in prairie soils caused by decreased use of ammonium sulphate fertilizer as a nitrogen source, reduced tillage and summerfallow lowering organic matter decomposition rates, higher nutrient requirements of hybrid canola varieties, and the absence of acid rain on the prairies.

Pyrite ($Fe_2S$)

A soil mineral that breaks down to form calcium and sulphate salts common in prairie soils, and dissolves in rivers and streams to contribute sulphur via irrigation water.

Sulphur Mineralization

The biological process that breaks down soil organic matter—which contains about $50\%$ of total soil sulphur—into plant-available sulphate under the same conditions as nitrogen mineralization.

Southern Alberta Irrigation Sulphur Contribution

The addition of an estimated $10\,\text{lbs/ac}$ of sulphur to agricultural soils through irrigation water carrying dissolved pyrite from rivers and streams.

Elemental Sulphur Oxidation

The microbial conversion of elemental sulphur into plant-available sulphate ($SO_4^{2-}$), which is favored by warm temperatures ($> 25^\circ\text{C}$), moist soils, a pH near $7$, and finely divided or ground sulphur particles.

Dr. S Malhi Research Study (1999–2002)

An Agriculture and Agri-Food Canada (Ag Canada) research project showing that elemental sulphur fertilizer required $2\text{ to }4\,\text{years}$ to become effective compared to ammonium sulphate.

Ammonium Sulphate Fertilizer

A fertilizer source that supplies sulphur directly in the plant-available sulphate ($SO_4^{2-}$) form, recommended for application in the spring at seeding when immediate crop uptake is required.

Elemental Sulphur Fertilizer

A lower-cost sulphur source that must be oxidized by soil microorganisms into sulphate over a period of $1\text{ to }3\,\text{years}$ ($2\text{ to }4\,\text{years}$ in field trials) before becoming plant-available, requiring application at least one year before the crop needs it.

Sulphur Immobilization

The biological tie-up of plant-available sulphate by soil microorganisms into organic matter, which typically occurs when residue carbon-to-sulphur (C:S) ratios exceed $200:1$.

Sulphur Volatilization

A pathway of sulphur loss where sulphate gases off into the atmosphere as hydrogen sulphide ($H_2S$) under warm, water-saturated soils and anaerobic conditions identical to denitrification.

Sulphate Leaching

The downward loss of sulphate out of the soil rooting zone during periods of high precipitation, occurring most readily in sandy soils with low organic matter content.

Buffering Capacity

The capacity of a soil to resist alterations in pH, which is higher in soils with high clay content due to their greater cation exchange capacity (CEC) and ability to bind more $H^+$ ions to exchange sites.

Soil Acidification by Elemental Sulphur

The process of lowering alkaline soil pH through the formation of sulphuric acid ($S + H_2O \rightarrow H_2SO_4$); lowering pH from $7.5$ to $6.5$ requires $300\,\text{lbs/ac}$ of elemental S in sandy soil, $600\,\text{lbs/ac}$ in silt loam soil, and $1200\,\text{lbs/ac}$ in clay soil.