reported here will have paramount importance to the revegetation plans for brackish and salt marsh 

 soils. The objective of this investigation was to determine the effect of soil drying, gypsum 

 addition, and electrical conductivity (EC) on soil properties that are related to urease activity. 



MATERIALS AND METHODS 



Soil and Sampling Procedures 



Soil samples were obtained from Clovelly soil series (clayey, montmorillonitic, euic, thermic 

 Terric Medisaprists) at a depth of 0-25 cm from an open area presently inundated by brackish 

 water located at Black Ridge, Hackberry, LA Eight composite samples were taken at intervals 

 covering a total area of 0.40 ha. Each sample was mixed, divided into three subsamples and stored 

 at 10-15 °C until the different treatments were applied. 



Soil Amendments and Treatments 



To evaluate the effects of soil drying, gypsum additions, and salinity on soil properties that are 

 related to urease activity, three experiments were conducted (Table 1). 



Experiment I 



The purpose of the first experiment was to determine the effect of drying on urease activity. 

 Triplicate 5-g samples were treated with 5 ml of 2,000 mg/L urea solution and incubated at 30 °C 

 for 5 hours. These samples were analyzed for urease activity following the procedure outlined by 

 Tabatabai (1982). The soil was extracted with 50 ml of 2 M KC1-PMA (Phenylmercuric acid) 

 solution as a urease inhibitor. The unhydrolyzed urea recovered in the KC1-PMA extract was 

 determined colorimetrically. The amount of hydrolyzed urea was calculated as the difference 

 between the urea added and the urea remaining. 



The effect of soil drying on some soil properties related to urease activity was also determined. 

 Triplicate 5-g samples of the two air-dried soil samples and one undried soil sample were analyzed 

 to determine soil pH, EC, and water-soluble cations. An automatic soil extraction apparatus was 



Table 1. Experimental variables and treatments. 



Experiment 



Treatments 



Incubation conditions 

 and urea addition 



I. Soil drying 



None - DO 



Air drying (1.5 months) - D1.5 



Air drying (3.0 months) - D3.0 



II. Gypsum additions 0, 5, 10, 20 mg/ha 



III. Salinity level 



0.1, 0.4, 0.8, 1.6 S/m (1:1 

 NaCl-CaC12 mixtures 



30 °C, 2000 mg/kg urea 

 30 °C, 2000 mg/kg urea 

 30 °C, 2000 mg/kg urea 



30 °C saturated, 10 

 days, 2000 mg/ha urea 



30 °C, saturated, 10 

 days, 2000 mg/ha urea 



87 



