Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Plant, Enviromental and Soil Sciences

First Advisor

Wayne H. Hudnall


Laboratory, greenhouse, and field experiments were conducted on brackish marsh soil of Hackberry, Louisiana (LA). This study was aimed to obtain detailed information on some soil- and water-based management factors that were applicable to the revegetation and productivity improvement of the area. This area was inundated by brackish-saline water, and is now open water, almost totally void of vegetation. The deteriorating productivity and continuous loss of vegetation in the study area can be related to the seasonal and temporal biochemical transformations. These transformations were significantly correlated to precipitation and minimum and maximum temperature in the area. Stochastic regression models were established to describe seasonal and temporal behavior of water and soil pH, electrical conductivity, total dissolved solids, and ionic strength in brackish marsh. The variability of individual soil properties in the study area as indicated by the coefficient of variations differed significantly (p = 0.01). A uniform application of any soil amendments like fertilizer or gypsum in the area that possessed spatially variable soil would result in over application in some parts of the area and under application in others. Soil drying significantly reduced urease activity in the area and was detrimental to the overall growth and yield of marsh vegetation. There was zero survival in the non-flooded plots except that marsh hay cordgrass had survival rate of 32.8%. The four species of marsh vegetation: Spartina patens Muhl. (marsh hay cordgrass), Distichlis spicata L. (salt grass), Paspalum vaginatum SW. (joint grass), and Scirpus americanus Pers. (freshwater three-square) responded significantly to N and gypsum (G) applications. Their overall yield response was described as DMY = 2.68 + 1.62N $-$ 0.98N$\sp2$ + 0.37N$\sp3$ $-$ 0.73G + 0.62G$\sp2$. Plots receiving 7 Mg gypsum ha$\sp{-1}$ produced significantly more dry matter yield (DMY) than did the control. This treatment increased the DMY of joint grass (5.04 to 8.08 Mg ha$\sp{-1}$), marsh hay cordgrass (1.90 to 6.91 Mg ha$\sp{-1}$, salt grass (0.97 to 2.79 mg ha$\sp{-1}$), and three-square (1.55 to 2.84 Mg ha$\sp{-1}$) in flooded plots. Significantly higher survival rates of plants were observed in flooded plots treated with gypsum than in the plots without gypsum or flooding.