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Effects of soil properties on crop yield and root carbon removal and impacts of a graduate-level professional development course

Monteza, Reynilda M.
The first chapter of this dissertation was conducted to evaluate the effect of inherent soil properties on crop performance and its relationship to surface soil health indicators. Using the soil profile sample data, the depths to the limiting layer were determined and regressed against the crop yields. Our data showed that only about 18% to 52% of the mean relative yield variability can be explained by the variability in inherent soil properties within each field. Considering the individual crop yields (i.e., wheat, soybean, corn, and sorghum) recorded from years unaffected by other external factors like weather conditions, the depth to limiting layer significantly influences and can explain 30% to >80% of the variability in crop yield.
The second chapter evaluated the impact of soil texture on root carbon removal during sieving and grinding processes and the estimation of the total soil carbon content from seven sites across Oklahoma under grassland use (i.e., switchgrass and pasture). It was found that as much as 35% of the carbon can be removed as roots. However, the influence of soil texture (i.e., sand) on this removal was only found to be significant in the subsoil (below 20 cm depth) and had less impact on the surface soil of 0-20 cm depth. Consequently, root carbon removal contributed 10-20 % of the total soil carbon for coarser textured soils and only about 5% for finer textured soils. This removal accounted for 0.8 to 5.6 Mg CO₂ -eq ha⁻¹ of carbon sequestered into the soil.
The third chapter evaluated the impact of a graduate-level professional development course on students’ career preparation and success. More than half of the respondents indicated confidence in their career plans after taking the course with most of them able to narrow down their choices while others reconsidered their plan. More than 80% of the respondents contributed their readiness and career success to the course and agreed that the course is an important part of the graduate program. Nevertheless, some respondents indicated the need to include more industry-related topics and discussions in the course.