smell of soil after rain is due to
Petrichor The term was coined in 1964 by two Australian CSIRO researchers, Isabel Joy Bear and Richard G. Thomas, for an article in the journal Nature.[1][2] In the article, the authors describe how the smell derives from an oil exuded by certain plants during dry periods, whereupon it is absorbed by clay-based soils and rocks. During rain, the oil is released into the air along with another compound, geosmin, a metabolic by-product of certain actinobacteria, which is emitted by wet soil, producing the distinctive scent; ozone may also be present if there is lightning.[3] In a follow-up paper, Bear and Thomas (1965) showed that the oil retards seed germination and early plant growth.[4]
Soil organic matter The concentration of SOM in soils generally ranges from 1% to 6% of the total topsoil mass for most upland soils. Soils whose upper horizons consist of less than 1% organic matter are mostly limited to desert areas, while the SOM content of soils in low-lying, wet areas can be as high as 90%. Soils containing 12-18% SOC are generally classified as organic soils.[5]