Submitted to: Computers and Electronics in Agriculture
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/15/2003
Publication Date: 3/15/2005
Citation: Kitchen, N.R., Sudduth, K.A., Myers, B.D., Drummond, S.T., Hong, S.Y. 2005. Delineating productivity zones on claypan soil fields using apparent soil electrical conductivity. Computers and Electronics in Agriculture. 46:285-308. Interpretive Summary: Starting in about the mid 1990's, many farmers began installing on their grain combines sensors for measuring grain amount as it was harvested in the field and then taking the data and creating yield maps. Collectively these sensors are called "combine yield monitoring systems." Some farmers now have as many as six or seven years of yield maps for the same field and have expressed interest in using these to identify those areas within fields that yield similarly from year-to-year. Areas with similar yield production have been called "productivity zones" or "yield zones." Farmers are interested in identifying productivity zones because key management decisions made early in the growing season (such as nitrogen fertilizer rate and seeding population) are based on what the expected yield would be. But what about fields that no yield mapping has been obtained? This study was conducted to answer the question of whether maps of productivity zones created from yield monitoring data would compare well to maps of productivity zones created using soil sensors (e.g., soil electrical conductivity (EC)). We found that about 60 to 70% agreement between zone maps made from EC and elevation and zone maps made with yield mapped information. We consider this level of agreement promising, especially considering the fact that there were many other factors that have an impact on yield other than EC and elevation. This means that farmers could reliably use EC and elevation for creating productivity zones for claypan soil fields where they do not have yield map information. Results of this study will benefit farmers and crop consultants by helping them develop cost effective ways for creating site-specific management plans.
Technical Abstract: 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 bulk 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. 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 3100). Elevation data was 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. The five SPZ outcomes that gave the highest Kappa coefficient were reported. Best performing combinations of ECa and elevation variables gave 60 to 70% agreement between YPZ and SPZ. We consider this level of agreement promising, especially considering the fact 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 could be reliably used for creating productivity zones on claypan soil fields.