Repository logo

Nitrogen fertilizer impacts on soil microbiome and tomato plant development


Nitrogen (N) fertilization largely supports agricultural production. Urea is a common N amendment used in agriculture and when overapplied it has negative consequences in the environment due to its highly labile and reactive form. Alternative fertilizers, such as controlled release fertilizers (CRF) have been designed to diminish the harmful effects of applied N. This thesis investigates and makes comparisons regarding N fertilizer types and their effects on microbial community composition and plant development. Both research questions were addressed by growing tomato (Solanum lycopersicum 'Rutgers') plants as the test crop, which serve as a good model crop for indoor greenhouse production and were grown to the vegetative stage in both studies covered in this thesis. The fertilizer types considered are urea, a quick releasing form of N fertilizer and Environmentally Smart Nitrogen (ESN), a controlled release fertilizer. The soil used in these studies was from a low N plot (5.2 mg/L NO3) from the Agricultural Research, Development and Education Center (ARDEC) in Fort Collins, Colorado. The first research question addressed in Chapter 2 examines how different types of N fertilizers compare under different soil conditions and fertilizer rates. Altering the soil microbiome through sterilization (via autoclave processing) allows us to understand how urea and a controlled release fertilizer compare in their impact on microbial community composition and N assimilation by a tomato crop. It was found in this study that the use of ESN promoted plant performance and enhanced soil nitrate concentration. The soil microbiome findings from this first experiment showed that high rates of nitrogen fertilization led to higher relative abundances of nitrifying bacteria species. The second research question addressed in Chapter 3 follows a developmental study to track how N fertilizer impacts tomato plant performance, rhizosphere microbiome assembly, and plant nutrient uptake by sampling weekly for eight weeks. It was found in this study that ESN enhanced nitrogen use efficiency and plant nitrogen uptake. The soil microbiome results indicated a shift in community structure at the middle stage of the rhizosphere development. By studying the plant growth and rhizosphere microbiome response to urea and a controlled release fertilizer applied soil, we can improve our understanding on N release rates and bacteria that are responsive to these agents. This is the first research to our knowledge examining N fertilization's impact on rhizosphere development during early to vegetative growth using, especially using a weekly sampling resolution.


Rights Access


soil microbiology
nitrogen fertilizer


Associated Publications