I'm assuming you have one record for every soil sample in the table where you base your sub-summary report.
It sounds like you can simply remove the Body part of the layout (click the part label in layout mode and then press the delete key.) to get what you want.
Place the Maximum and Minimum summary fields in the appropriate sub-summary part. A summary report with no "body' will list the sub-totals but will not list the individual records.
That work for you?