Soil samples analyzed for this test should be derived from at least 16 to 24 cores collected within an area not exceeding 10 acres. Areas with different soil types or management histories should be sampled separately.

The most appropriate sampling strategy varies with location. Collection of samples as suggested above provides information that can be used to identify future sampling strategies that are more efficient for the fields being tested.

Care should be taken to ensure the soil samples are collected in a manner that is not biased by the presence of corn rows or bands of fertilizer. At least 24 cores should be collected in fields having more than 50 lb. N/acre applied as anhydrous ammonia. Our results with ammonia treated fields have not been as consistent as other management.

Sampling bias can be minimized by collecting soil samples in "sets of eight" cores that have various assigned positions relative to corn rows. By this method, the person doing the sampling moves in a random pattern within the test area to select approximate positions for collecting cores. Each time a core is collected, however, its exact position is selected relative to the two nearest corn rows. The first core is collected in the row. The second is collected one-eighth of the distance between any two rows after moving to another part of the test area. The third is collected one-quarter of the distance between any two corn rows after moving to another part of the test area. The process is continued until the eighth core is collected seven-eighths of the distance between any two corn rows.

The soil from all cores should be crushed and thoroughly mixed in a clean pail before a sub-sample is removed for analysis.