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<br />I" <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />DISCUSSION <br /> <br />Field Backgrounds and Descriptions <br /> <br />Four individual fields were surveyed during the April 1996 trip. The first field was furrow <br />irrigated using a gravity flood system. The field shape was approximately rectangular, and <br />encompassed about 40 acres. This field was used for the Monday afternoon demonstration <br />exercises, and is referred to as field 1 in this report. The second and third fields were circular <br />shaped, and encompassed about 120 and 90 acres, respectively. Both fields were sprinkler <br />irrigated using center pivot systems, managed by the same farmer, and adjacently located. These <br />fields are referred to as field 2 and field 3 in this report, respectively. The last field was also <br />irrigated using a center pivot system, and encompassed about 90 to 95 acres. This field was <br />circular, however, about a 65 degree pie-shaped section was missing from the north-east portion <br />of the field (this latter section was being used as a livestock feeding area). This field is referred to <br />as field 4 in the remainder of this report. <br /> <br />The EM surveying and soil sampling was completed within about a 24 hour period in each <br />field. In field I all the EM survey and soij sample data was collected in the furrows. The soil <br />moisture in this field was marginal (less than 50% field capacity) and the field was not cropped. <br />Fields 2 and 3 were disced at the time of sampling. Additionally, the soil moisture levels in both <br />of these fields were extremely low, especially within the first foot of top soil. Field 4 was near <br />field capacity at the time of sampling, and was cropped with alfalfa. Centric systematic EM <br />survey grids were used in all four fields. The exact number of EM survey and soil sampling sites <br />were 93/15,169/18,95/10, and 93/15 survey/sample sites in fields 1,2,3, and 4, respectively. <br /> <br />The soil samples were extracted from each field in 30 cm increments down to a depth of <br />1.2 meters, The EM survey and soil sampling in each field were carried out using the standard <br />survey/sampling processes developed at the United States Salinity Laboratory by Dr. James <br />Rhoades (Rhoades, 1992; Rhoades, 1994). Details concerning the statistical sampling designs and <br />spatial salinity prediction techniques can be found in Lesch et a!., 1995a,b. All of the field specific <br />salinity estimates and spatial maps in this report were generated using the ESAP software package <br />(Lesch et a!., 1995c). <br /> <br />Soil Sampling Information <br /> <br />In the ESAP software package, sites are selected for soil sampling based on the fields <br />electromagnetic induction data. The goal of the sampling algorithm is to select representative <br />salinity data; i.e., to identify a spatially representative set of sample sites which reflect the general <br />salinity variability present within the field. Furthermore, in addition to soil salinity, other chemical <br />and/or physical properties can also be measured on the selected soil samples, and hence additional <br />information can be ascertained about the chemical and physical properties of the field. <br /> <br />'" <br />