Date on Honors Thesis

Fall 12-8-2022


Agricultural Science/Agronomy

Examining Committee Member

Iin Handayani, PhD, Advisor

Examining Committee Member

Megan Taylor, PhD, Committee Member

Examining Committee Member

David Ferguson, PhD, Committee Member


The fragipan layer in the soil is a naturally occurring subsurface layer that restricts water percolation as well as inhibits root growth. A fragipan layer can be found almost ubiquitously across Southwestern Kentucky. This limits how agriculturalists manage soils in this area. It has been recently discovered by the University of Kentucky that Annual Ryegrass roots produce 3,4 dihydroxyphenylpropionic acid (DHPPA) that reacts with this hardpan to weaken the layer. Certain bacteria, such as Escherichia coli, Lactobacilli, and Bifidobacteria can also synthesize DHPPA through a breakdown process of chlorogenic acid. This reaction typically happens in the human digestive tract. The objective of this study was to evaluate a biological solution to fragipan remediation through microbial activity. This experiment consisted of four treatments, each replicated three times. Soil samples from the fragipan layer were taken into the lab where they were treated in the following ways: control (all treatments applied to Bt soil horizon) (T0), annual ryegrass alone (T1), various bacteria species with coffee and tea grounds (T2), and various bacteria species with coffee and tea grounds and annual ryegrass (T3). Treatments were applied periodically to ensure that bacterial populations remained adequate and active. The bulk density, oven-dry mass, and air-dry mass of the soil samples were measured biweekly. This was completed to monitor the process of fragipan structure degradation. All data was statistically analyzed using Microsoft Excel. This study indicates no significant effect of the treatments (annual ryegrass, various bacteria species with coffee and tea grounds, and various bacteria species with coffee, tea grounds and annual ryegrass) on bulk density (soil compaction), oven-dried soil mass, and air-dried soil mass. Results from this study have implications that could impact how growers manage fragipan soils in Kentucky, as well as improve soil drainage, crop production, and sustainable agriculture.