2.4 



2.1 



J1.5H 



Si.« 



< 



Ul 

 (_) 



oO.fr 

 o 



0.3^ 



ao 



2.00 



a 89 



a is 



YZ2l 



Iron 



1.5 

 DRYING PERIOD (months) 



3.0 



Figure 3. Effect of soil drying on Mn and Fe concentrations. 



EC and the concentrations of water-soluble Na, Mn, Fe, Mg, and Ca increased as the time of soil 

 drying increased. Electrical conductivity increased from 0.39 to 3.88 S/m for an 895% difference 

 between undried soils containing 437% water and soils that were air dried for 3.0 months 

 containing 21% water. The impact of soil drying on the concentration of water-soluble Na, Mn, 

 Fe, Mg, and Ca was noted as an increase of 730%, 1,700%, 245%, 1,606% and 1,736%, 

 respectively, when compared with undried soil. This higher salt concentration resulting from drying 

 brackish marsh soil for 3.0 months could intensify the problem of nutrient toxicity and detrimentally 

 affect native vegetation and revegetation. Although all mechanisms involved are not well 

 understood, the significant reduction of urease activity at the end of a 3.0-month drying can be 

 partially attributed to the behavior of organic and inorganic colloids. Several workers have 

 suggested that the urease in soils is protected by humus or clay colloids (Conrad 1940; McLaren 

 1963, 1975). Similarly, Pettit et al. (1976) suggested that soil urease is usually immobilized within 

 the organic matter of the organo-mineral complex during humus formation. The organic matter 

 at sufficient moisture has pores large enough to allow the passage of substrate (urea and water) 

 and product (ammonia and carbon dioxide) molecules. If the same soils were subjected to 

 irreversible drying, the pore spaces would be blocked and this would tend to trap urease within the 

 crystal lattices. The escape of the urease itself is then prevented. This blocking mechanism 

 associated with irreversible drying of marsh soils rich in organic matter will partially or totally 

 prevent the contact between the soil colloid and the applied urea, ultimately decreasing the amount 

 of urea hydrolysis. 



91 



