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Stratified random sampling is similar to simple random sampling except that the area 363 of interest is divided into smaller sub-areas. These sub-areas are selected based on known 364 variations in the soil or other factors of interest. Samples are collected within each sub- 365 area in a random manner as described above. The advantage of stratified random 366 sampling is that a researcher can compare results between the sub-areas and possibly 367 correlate results to the factor of interest. 368 Systematic sampling is comprised of sampling at predetermined points or intervals, 369 such as points along parallel lines or intervals based on the distance from a point. This 370 type of non-random sampling is performed in order to ensure an area is well understood. 371 Systematic sampling is useful for sampling after an outdoor activity with the sampling 372 lines informed by the activity and its location. 373 Composite samples are those that are comprised of a number of smaller samples 374 mixed together in order to reduce the cost of analyzing each sample individually. For 375 example, random samples collected within a sub-area can be composited and analyzed to 376 produce a single result for that sub-area. Once prepared, the composite sample can no 377 longer provide any information on the variation among the individual samples. In order 378 for results from composited samples to be valid, certain conditions must be met. First, all 379 composite samples should be comprised of an equal number and mass of individual 380 samples; second, there must be no interactions between the individual samples as these 381 interactions could skew the results; and third, the study’s objectives must include 382 obtaining an unbiased estimate of the mean (10). 383 Once the sample type is determined, it is recommended to follow sound sampling 384 practices prior to using the soil sample. Parameters such as how much soil is required for 385

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