THE EFFECT OF DRYING AND ELECTRICAL CONDUCTIVITY 

 ON UREASE ACTIVITY IN A BRACKISH MARSH 1 



G. C. Sigua and W.H. Hudnall 



Department of Agronomy, Louisiana Agricultural 



Experimental Station, LSU Agricultural Center 



Baton Rouge, LA 70803 



ABSTRACT 



Surface horizons of brackish marsh soils collected at Hackberry, LA were studied to determine 

 the effect of soil drying and electrical conductivity on soil properties that are related to urease 

 activity. Soil drying significantly reduced urease activity and increased the conductivity and 

 concentration of water-soluble Na, Fe, Mn, Mg, and Ca. There was a significant decrease in soil 

 pH at the end of 3 months drying. These soils and soil-related factors were significantly correlated 

 to soil moisture. There was a general reduction in urease activity as levels of conductivity 

 increased. Addition of gypsum did not result in any significant increase of urease activity, but there 

 was a numerical increase of 50% in urease activity of soil treated with 20 Mg/ha more than the 

 control. An equation is presented that best accounts for variation in urease activity in brackish 

 marsh soil. 



INTRODUCTION 



Wetland loss in Louisiana is a widely recognized problem. Each year, Louisiana loses 

 approximately 50 mi to natural subsidence, erosion, and human intervention (Louisiana 

 Department of Natural Resources 1986). Marshes, as part of our land and natural water regime, 

 are irreplaceable natural resources that must be preserved. One of the possible solutions for saving 

 wetlands from natural and accelerated losses is through restoration of vegetation. Restoration with 

 suitable marsh vegetation usually requires some elaborate management practices that include soil 

 drainage, fertilization, and various other cultural practices. Soil drainage and fertilization are the 

 two most important components for two reasons: a) soil drainage, which is especially important at 

 the seedling or early stage of growth establishment, is likely to affect the microbial and 

 physicochemical properties of the soil, and b) although most marsh soils in Louisiana contain 

 considerable amounts of organic carbon (OC), the marsh is most limited in N (Broome et al. 1975; 

 Patrick and DeLaune 1976; Mendelssohn 1979; Smart and Barko 1980). 



The work reported here identifies some of the probable effects on soil properties associated 

 with drying brackish marsh for an extended period. Data are presented on the causes of low N 

 availability in the marsh and the relationships between soil urease activity and soil properties at 

 different soil moisture contents. Although there are several studies limited to well-drained soils 

 (Conrad 1940; Stojanovic 1959; Zantua and Bremner 1975, 1976; Pettit et al. 1976; Zantua et al. 

 1977; Savant et al. 1985) and a few from waterlogged rice soils (DeLaune and Patrick 1970; Islam 

 and Parsons 1979; Sahrawat 1980), the general principles and concepts of N availability and losses 

 are applicable to N availability in the marsh environment. The ongoing research and the results 



Approved for publication by the Director of Louisiana Agricultural Experiment Station as 

 Manuscript No. 88-09-2372. 



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