Rapid soil harvesting using a novel soil auger system for farm‐scale soil carbon estimates.

Soil sampling at the landscape scale is increasingly in demand for assessing C sequestration projects in agroecosystems. Efforts to decrease sampling costs across large areas have thus far largely ignored improved soil harvesting tools as a means of decreasing sampling time and effort. Rigorous analysis of trade‐offs in speed and accuracy among soil harvesting methods is needed. Here, we compare two different methods of soil sampling soil, a standard push probe and a novel drill‐auger system, which were used to collect soils for analysis of total C by dry combustion. We designed sampling plots to compare soil C concentrations at increasing spatial scales to understand the difference in soil C concentrations between methods relative to spatial heterogeneity. We sampled two farms in Upstate New York, one conventional and one organically managed, to assess the impact of these methods across relevant farm practices. We found that probe and auger methods provide indistinguishable soil carbon estimates at both farms. The difference between paired probe and auger samples taken less than 0.15 m apart was 0.22%, an amount equivalent to the difference in C concentrations at points 2 m apart and less than the difference at points 10 m apart. Using the soil auger was up to three times faster than using the push probe—a saving of 7 h of sampling time to inventory the two farms studied. Lowering inventory cost is a critical step in demonstrating the feasibility of soil carbon sequestration as a component of climate smart agriculture. The results presented indicate that the drill‐auger system is preferable to the push probe method for farm‐scale soil carbon inventory. Core Ideas: One component of lowering soil sampling cost is to increase the efficiency of in‐field sample collection.Comparison of a soil probe to a drill‐auger demonstrates that C estimates are indistinguishable at the farm scale.The difference between methods at <0.15 m is less than the spatial heterogeneity in %C at a distance of 2 or 10 m.The drill‐auger is 1.75–3x faster than the probe that translates to an approximate savings of $1.18 per acre.Considering the trade‐offs of sampling methods can save significant time and resources in large‐scale projects. [ABSTRACT FROM AUTHOR]