SPADA Meeting Book

Systematic sampling is comprised of sampling at predetermined points or intervals, 362 such as points along parallel lines or intervals based on the distance from a point. This 363 type of non-random sampling is performed in order to ensure an area is well understood. 364 Systematic sampling is useful for sampling after an outdoor activity with the sampling 365 lines informed by the activity and its location. 366 Composite samples are those that are comprised of a number of smaller samples 367 mixed together in order to reduce the cost of analyzing each sample individually. For 368 example, random samples collected within a sub-area can be composited and analyzed to 369 produce a single result for that sub-area. Once prepared, the composite sample can no 370 longer provide any information on the variation among the individual samples. In order 371 for results from composited samples to be valid, certain conditions must be met. First, all 372 composite samples should be comprised of an equal number and mass of individual 373 samples; second, there must be no interactions between the individual samples as these 374 interactions could skew the results; and third, the study’s objectives must include 375 obtaining an unbiased estimate of the mean (8). 376 Once the sample type is determined, it is recommended to follow sound sampling 377 practices prior to using the soil sample. Parameters such as how much soil is required for 378 measuring soil properties and for the experiment or testing could be calculated prior to 379 collecting the sample. It is also recommended to consider how many samples or tests will 380 be required to provide defensible results. Several websites provide guidance on sampling 381 practices and experiment set-up that could be considered during planning phases of using 382 the soil samples (9, 10, 11). Considering sampling error prior to collecting and using soil 383 could provide more sound results. 384

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