Investigating the use of polyhalite as a potassium fertiliser in rice plants

Potassium (K) is essential for plant growth and health, featuring in a vast array of activities within the plant. Deficiencies in K nutrition cause serious issues regarding plant growth and crop yield. Polyhalite (K2SO4.MgSO4.2CaSO4.2H2O) is a hydrated evaporate mineral which can be used directly as a K fertiliser. However, there has been limited work on the suitability and efficacy of polyhalite compared to traditionally used K fertilisers such as potassium chloride (KCl) and potassium sulphate (K2SO4). The aims of this thesis were to explore the efficacy of polyhalite as a K fertiliser compared to KCl and K2SO4 and evaluate its effect on rice growth traits and nutrient content in both balanced and unbalanced fertiliser regimes. No differences in rice biomass were discovered between different K fertiliser regimes. However nutrient analyses showed inconsistent results to the different K fertilisers. A range of rice cultivars was then assessed for their response to different K fertiliser regimes. No significant variation between individual cultivars was observed in response to different K fertiliser sources with respect to biomass or nutrient content. Additionally, grouping cultivars by potassium use efficiency provided few changes in nutrient content responses. Finally, microbial communities in the plant rhizosphere were characterised for taxonomic diversity to determine if and how these properties are affected by different K fertilisers. In nutritionally balanced fertiliser regimes, the bacterial populations of the rice plant rhizosphere were not influenced by treatment although harvesting timepoint did affect their composition. Conversely, comparison of unbalanced K regimes revealed differences in bacterial species composition, but little change was observed in the total number or distribution of species of the bacterial populations. The findings of this work can be used to inform similar investigations using polyhalite as a K fertiliser as well as future work investigating K fertiliser effects on microbial populations.