used to extract the water-soluble cations. Concentrations of these cations were analyzed by using 

 an inductively coupled plasma spectrophotometer. 



Experiment II 



The objective of Experiment II was to determine the effect of gypsum additions on urease 

 activity. Triplicate 5-g samples of saturated soil were treated with four rates of gypsum (0, 5, 10, 

 20 mg/ha) and incubated at 30 °C for 10 days. After incubation, the samples were treated with 

 2000 mg/L of urea solution. Urease activity of the soil was determined by following the same 

 procedures used in Experiment I. 



Experiment III 



The purpose of Experiment III was to determine the effect of different levels of EC on urease 

 activity. Saturated samples were split into 12 subsamples and EC was adjusted to 0.1, 0.4, 0.8, and 

 16 S/m by adding artificially salinized water that contained 1:1 NaCl-CaCl mixture, and incubated 

 at 30 °C for 10 days. An application of 2,000 mg/L urea was added to each soil. Urease activity 

 was determined following the procedures outlined in Experiment I. 



RESULTS AND DISCUSSION 



Soil and Water Analyses 



Some properties of the representative soil profile are given in Table 2. Surface soils (Oal + 

 Oa2) or the organic horizons have a pH of 6.50 to 6.62; OC ranged from 20.23% to 33.72%; and 

 EC ranged from 0.21 to 0.36 S/m. A general increase in the concentration of water-soluble cations 

 was observed with depth. 



A water sample from the study area had a pH of 6.8, EC of 0.7 S/m, 0.49 mg/L Fe, 897 mg/L 

 Na, 189 mg/L Mg, 85 mg/L Ca, and 145 mg/L S. 



Urease Activity and Soil Related Properties 



Urease activity of brackish marsh soil as affected by soil drying is given in Figure 1. A 

 significantly higher rate of urease activity was observed in the samples dried for 1.5 months, the 



Table 2. Selected soil chemical properties of undried soils. 



88 



