Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: April 23, 2006
Publication Date: May 23, 2006
Citation: Corwin, D.L. 2006. Eca-directed soil sampling for characterizing spatial variability: monitoring management-induced change. American Geophysical Union. Paper No. NS21B-02 Technical Abstract: Characterizing spatial variability is an important consideration of any landscape scale soil related problem. Geospatial measurements of apparent soil electrical conductivity (ECa) are useful for characterizing spatial variability by directing soil sampling. The objective of this presentation is to discuss equipment, protocols, sampling designs, and precautions for conducting an ECa survey to characterize spatial variability. To demonstrate its flexibility, data will be presented for applications including modeling of NPS pollutants in the vadose zone, precision agriculture, and soil quality assessment. In particular, a preliminary spatio temporal study of management-induced changes to soil quality will be demonstrated for a drainage water reuse study site. The spatio temporal study used electromagnetic induction ECa data and a response surface sampling design to select 40 sites that reflected the spatial variability of soil properties (i.e., salinity, Na levels, Mo, and B) impacting the intended agricultural use of a saline sodic field in California's San Joaquin Valley. Soil samples were collected in August 1999 and April 2002. Data from 1999 indicate the presence of high salinity, which increased with depth, high sodium adsorption ratio (SAR), which also increased with depth, and moderate to high B and Mo, which showed no specific trends with depth. The application of drainage water for 32 months resulted in leaching of B from the top 0.3 of soil, leaching of salinity from the top 0.6 m of soil, and leaching of Na and Mo from the top 1.2 m of soil. The leaching fraction over the time period from 1999-2002 was estimated to be 0.10. The level of salinity in the reused drainage water (i.e., 3-5 dS/m) allowed infiltration and leaching to occur even though high sodium and high expanding-lattice clay levels posed potential water flow problems. The leaching of salinity, Na, Mo, and B has resulted in increased forage yield and the quality of those yields. Preliminary spatio temporal analyses indicate at least short term feasibility of drainage water reuse from the perspective of soil quality when the goal is forage production for grazing livestock. The implications of this research extend well beyond the provincial applications of assessing drainage water reuse in central California to the global potential of ECa-directed soil sampling for evaluating farm-induced management ramifications on soil and for characterizing soil spatial variability.