SOIL ORGANIC MATTER CONTENTS IN THE SHALLOW SALINE AQUIFER BELOW NAS LEMOORE IN WESTERN SAN JOAQUIN VALLEY, CALIFORNIA

The Naval Air Station Lemoore (NASL) is located in the western central part of California’s San Joaquin Valley which has long been affected by soil and groundwater salinization due to drainage of irrigated agricultural fields. The soil organic matter content of the shallow saline aquifer at NASL is physically delineated in this study in conjunction with a larger study that was conducted to evaluate soil and groundwater conditions.

In arid soils, the natural soil organic matter content (OMC) is usually small (less than 2%), but its effect on soil functions are profound. Soil organic matter provides much of the soil’s cation exchange capacity. It is largely responsible for the formation of soil aggregates which increases soil aeration and water-holding capacity. It also contains large quantities of plant nutrients and acts as slow-releasing nutrients. Furthermore, organic matter supplies energy and body-building constituents for most of the microorganisms. For all these reasons, it is necessary to measure the soil OMC in order to determine the soil quality.

The soil OMCs were measured using the oven and furnace drying methods in the lab. Samples were taken from 450 soil cores obtained from 28 newly installed groundwater observation wells drilled to depths of 20-25 ft. The measuring results were plotted in 2D and 3D software to assess the spatial patterns of soil OMC at NASL.

Results show that the soil OMC is generally high in the surface soil (> 3%). It decreases along the depth of the aquifer but never become less than 2%. The soil texture within the 20-ft depth varies from sand to silt clay but mostly loams. All indicators show that the soil has good texture, high organic matter and nutrients, thus is suitable for growing shallow- and deep-rooted plants if soil and groundwater salinity is controlled.