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sample collection, then soil pH and water content should be measured immediately, and 571 the remaining characteristics measured at a later time. Soil pH and dry weight should be 572 monitored during the course of the experiment as these could affect the performance of a 573 biothreat agent detection method or system. If a soil is too moist, the soil can be dried to a 574 more acceptable moisture content by air drying with frequent mixing in a sterile 575 environment until the moisture content is low enough. Drying a soil is not recommended 576 unless the method or system being evaluated requires dryer soil. Avoid collecting soil 577 samples after a weather event in order to avoid overly moist soil. To add moisture to a 578 soil, sterilized water can be sprayed onto the soil while monitoring the increase in mass 579 by weighing the soil while spraying. Once added, mix the soil well to ensure even 580 distribution of the added moisture. 581 Soils should be kept in the dark and preferably in an incubator. The container lid 582 should be either opened regularly to ensure a consistent atmosphere or placed ajar with 583 sterile cloth over the container opening preventing contamination in a humidity- 584 controlled incubator. 585 If planning a time series experiment, either a large batch experiment or sacrificial 586 replicates can be used. During each sampled time point, the water content of the soil 587 should be measured as well in order to report the data in soil dry weight. 591 multiple environments and under multiple seasonal conditions. Typically, open-air field 592 testing is conducted using a truth box of ca. ½ km 2 in area. Multiple ground truth 593 588 589 590 10.2 Outdoor Testing Set-up Field testing designed to simulate a biothreat agent release should be carried out in

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