Niraj Yadav

Candidature

PhD Candidate

Thesis Title

Liquid gold: Understanding plant and soil Interactions with nutrients in a circular economy

Project Summary

My research focuses on the development and optimisation of urine-derived fertiliser (UrVAL) as a sustainable alternative to conventional fertilisers. This work aligns with the principles of the circular economy, aiming to recycle essential nutrients like nitrogen, phosphorus, and potassium from human waste streams back into agricultural systems. By leveraging an often-underutilised resource, my research seeks to reduce the environmental footprint of traditional agriculture while closing the nutrient loop.
A central aspect of my work is understanding how urine-derived fertilisers interact with soil systems at a chemical, physical, and biological level. The soil’s ability to support plant growth is deeply influenced by the availability of nutrients and minerals, which are subject to complex interactions in the soil’s aqueous phase. In this system, essential nutrients like nitrogen, phosphorus, and potassium exist in dissolved forms that plants can uptake, but their availability is governed by a host of factors including soil pH, cation exchange capacity (CEC), and redox potential.
In the soil, nutrient transformations are driven by various chemical processes. Nitrogen, for example, can be present in multiple forms such as ammonium (NH₄⁺) or nitrate (NO₃⁻), each responding differently to the soil’s pH and microbial activity. Phosphorus, a crucial nutrient often limited in availability, can bind to metal ions like iron or aluminum, forming metal-phosphate complexes that precipitate out of the soil solution, especially in acidic conditions. These interactions reduce phosphorus availability to plants, requiring careful management of soil conditions to ensure nutrient accessibility.
Equally important are the roles of metal oxides and hydroxides in the soil, particularly those of iron, aluminum, and manganese. These metals can become more soluble in acidic environments, leading to the release of toxic metal ions that can impair plant roots and disrupt the uptake of other nutrients such as calcium and magnesium. This dynamic is particularly critical in the vadose zone, the area of soil just above the water table, where the soil solution interacts with mineral surfaces. The processes of mineral dissolution, ion exchange, and metal oxide formation in this zone directly impact nutrient mobility, retention, and plant health.
Understanding these nutrient-mineral interactions is essential for sustainable fertiliser management. It is not simply the amount of fertiliser applied that determines plant health, but also how nutrients interact with the soil matrix, their potential to leach, and the risk of metal toxicity. In my research, I am investigating how urine-derived fertilisers like UrVAL influence these soil processes, with particular focus on how nutrient dynamics, metal solubility, and soil pH can be managed to prevent soil degradation while promoting long-term soil fertility.
At the fertiliser end-user level, it is critical to comprehend these soil chemistry interactions. Mismanagement of nutrient inputs can lead to unintended consequences, such as nutrient leaching, soil acidification, and metal toxicity, all of which compromise plant health and agricultural sustainability. My work provides insights into how organic fertilisers can be effectively integrated into farming systems, ensuring that nutrient cycles are optimised for both productivity and environmental stewardship. By advancing our understanding of the chemistry of nutrient transformations, we can better manage the delicate balance between promoting plant growth and maintaining soil health.

Supervisors

Jeff Powell, Jason Reynolds, Serhiy Marchuk, Bernadette McCabe

Publications

1. Tan, W., Yu, H., Xiao, H., Wang, T., Hossain, M.A., Wu, Y., Yadav, N. (2024). "Radiocarbon evidence of organic carbon turnover response to grassland grazing: A soil aggregate fraction perspective," Sustainable Horizons, 12, 100115.
2. Xiao, H., Liu, Y., Yu, H., Yadav, N. (2023). "Combined toxicity influence of polypropylene microplastics and di-2-ethylhexyl phthalate on cucumber," Plant Physiology and Biochemistry, 107811.
3. Anand, U., Pal, T., Yadav, N. (2023). "Current scenario and future prospects of endophytic microbes for stress management," Microbial Ecology, 1-32.
4. Yadav, N., Ronen, Z., Arye, G. (2022). "Distribution of pathogens and antibiotic resistance in SAT systems," EGU General Assembly 2022.
5. Okorie, B. O., Yadav, N. (2022). "Influence of slope and management on topsoil fertility at Nsukka Campus," Medicon Agriculture & Environmental Sciences, 2, 25-33.
6. Okorie, B. O., Yadav, N. (2022). "Effects of different tillage practices on soil fertility," International Journal of Agriculture and Environmental Research, 8(1), 176-193.