Murray State Theses and Dissertations

Abstract

This study evaluated whether Mehlich III soil nutrient sufficiency ratings reliably predict plant nutrient status and chlorophyll response across contrasting compost application histories. A greenhouse pot experiment was conducted with Chijimisai (Brassica rapa) planted in three treatment soils that had no compost (T1), moderate compost history (T2), and long-term hog manure compost application (T3). Plant performance was assessed through weekly shoot length and chlorophyll content (SPAD) measurements, leaf number at maturity, and leaf tissue nutrient analysis conducted at harvest. Soil test results indicated adequate to high nutrient levels across all three treatments. Leaf tissue analysis, however, revealed substantial nutrient imbalances that intensified with increasing compost exposure. Tissue concentrations of zinc (Zn) and manganese (Mn) increased markedly from T1 to T3, while leaf iron (Fe) concentration declined substantially in the high-compost treatment despite soil Fe levels rated as sufficient. This pattern is consistent with established principles of micronutrient antagonism among Zn, Mn, and Fe as documented in the plant nutrition literature. Concurrently, final SPAD was significantly lower in T3 than in T1 and T2 (p < .001, η² = .752), a result consistent with chlorophyll impairment associated with elevated tissue Zn. The T2 treatment produced superior plant performance across all measured variables, suggesting that the benefits of compost amendment are optimized at moderate application levels and diminish as progressive micronutrient accumulation occurs at higher compost histories. Potassium (K) and magnesium (Mg) concentrations in leaf tissue were below sufficiency thresholds in all treatments despite soil test ratings of adequate, further demonstrating the discrepancy between soil nutrient availability and actual plant uptake. These findings demonstrate that soil nutrient sufficiency ratings did not reliably predict plant nutrient status or chlorophyll response in contrasting compost histories under the conditions of this study. Observed patterns of soil–plant nutrient decoupling were consistent with theoretical frameworks of micronutrient antagonism. These results support the integration of leaf tissue analysis with routine soil testing as a more comprehensive diagnostic approach in compost-amended vegetable production systems.

Year manuscript completed

2026

Year degree awarded

2026

Author's Keywords

Chlorophyll (SPAD), Compost-amended soils, Iron deficiency, Leaf tissue analysis, Nutrient antagonism, Soil nutrient sufficiency

Degree Awarded

Master of Science

Department

Agriculture

College/School

Hutson School of Agriculture

Dissertation Committee Chair

Trent Wells

Thesis Advisor

Alyx Shultz

Committee Member

Alyx Shultz

Committee Member

Iin P. Handayani

Committee Member

Kristie Guffey

Document Type

Thesis

Additional Files
CJ Thesis Defense.pptx (2647 kB)
Defense Presentation
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