Delineating productivity zones on claypan soil fields using apparent soil electrical conductivity

Efficient and cost-effective methods are needed for delineating sub-field productivity zones to improve soil and crop site-specific management. This investigation was conducted to answer the question of whether apparent soil electrical conductivity (ECa) and elevation could be used to delineate productivity zones (SPZ) for claypan soil fields that would agree with productivity zones delineated from yield map data (YPZ). Ten and seven years of combine-monitored yield maps were available for two Missouri claypan soil fields, designated Field 1 and Field 2, respectively. The fields were generally cropped in corn and soybean. Soil ECa data were collected with a non-contact, electromagnetic induction-based ECa sensor (Geonics EM38) and a coulter-based sensor (Veris model 3100). Elevation data were collected using a real-time kinematic GPS. Unsupervised fuzzy c-means clustering was independently used both on yield data to delineate three YPZ and on combinations of ECa and/or elevation data to delineate three SPZ. Outcomes of YPZ and SPZ were matched and agreement calculated with an overall accuracy statistic and a statistical index called the Kappa coefficient. Best performing combinations of ECa and elevation variables gave 60-70% agreement between YPZ and SPZ. We consider this level of agreement promising, especially considering that there were many other yield-limiting factors unrelated to ECa and elevation. Generally, multiple variables of ECa and elevation were better than a single variable for generating SPZ. The specific combinations of ECa and/or elevation variables that gave highest agreement between YPZ and SPZ were field specific. Based on these findings, we conclude ECa and elevation measurements can be reliably used for creating productivity zones on claypan soil fields.