LS08AcidSulf HM

Potential acid sulfate soil: 

Potential acid sulfate soil Soils which become acid when drained due to oxidation of pyrite (FeS2) WRB Potential acid sulfate soil contains sulfidic soil material that contains pyrite but has not oxidized to an extent that the soil-pH dropped to a value below 3.5

Formation of pyrite: 

Formation of pyrite Fe2O3 + 4SO42- + 8CH2O + 1/2O2 = 2FeS2 + 8HCO3- + 4H2O Iron must be present Sulfur must be present Anaerobic condition must prevail to reduce SO42- & Fe3+ Organic matter as energy source for the microbes The process increases pH

Location of pyrite in the landscape: 

Location of pyrite in the landscape In delta regions and lagunes where sea water is meeting fresh water. Inland wetland areas which are enriched with ferro iron and sulfate from higher parts of the landscape Soil material with high content of pyrite is called sulfidic soil materials

Fluvisols and gleysols: 

Fluvisols and gleysols

Histosols: 

Histosols

Oxidation of pyrite: 

Oxidation of pyrite If the soil is drained pyrite will be oxidized: 4FeS2 + 15O2 + H2O -> 2 Fe2(SO4)3 + 2H2SO4 pH drops significantly and not only ferro iron but also ferri iron will be mobile. Soils which become very acid due to oxidation of pyrite are classified as actual acid sulfate soils

Oxidation of pyrite might forma sulfuric horizon: 

Oxidation of pyrite might form a sulfuric horizon Definition of sulfuric horizon A sulfuric horizon must: have a soil-pH < 3.5 (in 1:1 water suspension); and have yellow/orange jarosite [KFe3(SO4)2(OH)6] or yellowish-brown schwertmannite [Fe16O16(SO4)3(OH)10.10H2O] mottles; or concretions and/or mottles with a Munsell hue of 2.5Y or more and a chroma of 6 or more; or underlying sulfidic soil materials; or 0.05 percent (by weight) or more of water-soluble sulphate; and have a thickness of 15 cm or more.

Agriculture problemsactual acid sufate soils: 

Agriculture problems actual acid sufate soils Low soil pH Aluminium toxidity Salinity (from sea water) Phosphorous deficiency (precipitation of aluminiumphosphates) H2S toxidity if flooded N-deficiency due to slow microbial activity Ingeneering problems as soil acidity attacks steel and concrete structures

Environmental problemsOchre polution of Danish watercourses: 

Environmental problems Ochre polution of Danish watercourses Severe ochre polution of Danish streams has frequently occured due to drainage of farmland. The ochre polution was believed to be due to oxidation of pyrite. In order to prevent ochre polution of the streams a mapping of potential acid soils was conducted The mapping should be done within a 3 years period Based on the mapping a legislation should be made to stop the ochre polutions of the streams.

Normal stream: 

Normal stream

Ochre from drains: 

Ochre from drains

Ochre poluted streams: 

Ochre poluted streams

Sampling area: 

Sampling area

Camp site and equipment for mapping potential acid sulfate soils: 

Camp site and equipment for mapping potential acid sulfate soils

Sampling area: 

Sampling area

Travelling to sampling site: 

Travelling to sampling site

Augering in wetland: 

Augering in wetland

Samples: 

Samples

Soil description scheme: 

Soil description scheme

Determination of colour and pH: 

Determination of colour and pH

Potential acidityanalytical results for lime free samples: 

Potential acidity analytical results for lime free samples A sample is potential acid sulfate if: pH drop below 3.0 within 16 weeks of oxidation and pH drops more than one unit within that period

Potential aciditylime containing samplesPotential acid sulfate if: %pyrite x 34 meq/100g > (Ca + Mg) meq/100g : 

Potential acidity lime containing samples Potential acid sulfate if: %pyrite x 34 meq/100g > (Ca + Mg) meq/100g

Potential acid sulfate soil classes: 

Potential acid sulfate soil classes Class 1: > 50% acid sulfate soil profiles Class 2: 20-50% acid sulfate soil profiles Class 3: 2-20% acid sulfate soil profiles Class 4: <2% acid sulfate soil profiles An acid sulfate soil profile is a profile containing at least one acid sulfate soil sample

Map showing potential acid sulfate soils: 

Map showing potential acid sulfate soils

Red 50%-100%Yellow 20%-50%Green 20%-2%Blue: <2%Potential acidsulfate soil: 

Red 50%-100% Yellow 20%-50% Green 20%-2% Blue: <2% Potential acid sulfate soil

Area statistics: 

Area statistics

Ochre investigation areasif the farmer wants to drain: 

Ochre investigation areas if the farmer wants to drain