Offered Bachelor Thesis

Sulfate fertilization has been proposed as a way to reduce As content in rice grains and greenhouse gas emissions from paddy soils. However, there are contradictory results where, in some cases, sulfate fertilization increases As mobility or greenhouse gas emissions. Recent observations from experiments done with a paddy soil chronosequence (i.e. soils from which we know how long they have been used for rice production) makes us think that changes in different biogeochemical parameters with increasing paddy soil age (such as organic carbon or amorphous iron phases) could explain these differences.

To test this hypothesis, we will carry out incubation experiments with these paddy soils, where we will spike sulfate to simulate fertilization. Then, we will track how different biogeochemical cycles are influenced by this fertilization, including greenhouse gas emissions and As mobility and speciation and other related biogeochemical cycles such as that of Fe and S.

This study is part of a PhD project, and upon positive results, it would yield a scientific publication (possibility for coauthorship).

Keywords: Biogeochemical cycling, agricultural management, greenhouse gas emission mitigation.

We have been working with a set of paddy soils from a chronosequence (soils from which we know how long they have been used for rice cultivation). The evolution of these soils means that they have biogeochemical properties that follow a pattern (e.g., the older a soil is, the more greenhouse gases it emits or more phytotoxic As is formed in the porewater, possibly affecting rice quality). Two of the soils from this chronosequence have been affected so that they don’t follow these trends. One of them was irrigated with water contaminated with fossil fuels, affecting the microbial activity in the soil and thus, affecting the general biogeochemical cycling. The second soil suffered a physical disturbance due to the removal of the top layer of soil, where most of the organic carbon accumulates in paddy fields and where most of the microbial activity takes place.

This work would evaluate possible ways to restore the integrity of these soils (i.e., make them fit the trends of the chronosequence) by different methods, such as inoculating a healthy microbial community or adding organic carbon to restore the properties that the soils have lost. It involves incubation experiments and several different analytical techniques that would help us understand the dynamics of C, Fe, S, and As to better understand these soils and how both chemical and physical disturbances affect the microbiology and geochemistry of paddy soils.

This study is part of a PhD project, and upon positive results, it would yield a scientific publication (possibility for coauthorship).

Keywords: soil restoration, soil health, biogeochemical cycling, site remediation.