An automated on-the-go soil sampler was developed as part of a soil nitrate mapping system that collects data for precisely analyzing small-scale variation in soil NO3-N. An essential requirement of the sampler is the ability to reliably collect a soil sample of known "weight" (mass). It was hypothesized that if a uniform bulk density sample could be collected in a device of fixed volume, then the mass of the sample would be known and constant. The sampler employs a woodsaw blade to cut a 15 cm deep slot in the soil at a sampling location as it travels forward and to throw a spray of finely chopped soil into a fixed-volume pocket milled into the surface of an automatically positioned flat-belt transfer conveyer. Performance testing of the sampler was conducted in five fields. Coefficient of uniformity (CU) for sample bulk density was 92.9%, which produced less than a 5.5% deviation in sample delivered weight (DW) in 83.6% of the cases. Mean DW error was 10.9% and DW CU was 82.0%, mostly due to localized high clay content in three of the fields. Mean pocket fullness (PF) was 89.9%, and PF CU was 83.6%. Pocket fullness was linearly correlated with DW (R2 = 0.979, n = 140). It was concluded that the sampler's "uniform bulk density" design principle was validated for all intents and purposes of field use. Delivered weight uniformity, particularly when sampling in clayey soils, should be increased by further improving the design .
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