Updated November 2, 2020:
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The results of both 2018 and 2019 Pennsylvania Soybean Board projects on “Using Precision Agriculture Data to Define and Refine Soil Fertility Management in Soybean Production” were consistent in their findings. Soil EC maps created by Veris sensors or other technologies that measure apparent soil electrical conductivity can be used successfully to divide fields into zones that have different soil fertility requirements. We observed that EC maps at different sites could differentiate between zones of fields with different lime, P, and K fertilizer requirements. However, there were sometimes differences in fertilizer recommendations within soil EC zones that could not be differentiated by the soil EC maps. Therefore, EC maps improved the spatial resolution at which fertilizer and lime applications can be made within a field, but may not capture every level of variability that exists within a field. Nonetheless, our study suggests that soil EC mapping is a useful tool that farmers should consider for developing soil sampling and fertilizer recommendations on a zone by zone basis.

The results of our fertilizer response plots, which harnessed natural variations in soil test levels between and within fields, generally confirmed that existing soil test critical levels for P, K, and S used by Penn State and the fertilizer recommendations to maintain soil test levels in the optimum range made by Penn State are sufficient to support modern soybean genetics and production practices. This is the first study to evaluate soil test S critical levels in soybean production in Pennsylvania, and it is noteworthy that the critical S level determined in previous research for corn production is similar to that determined here for soybean production. A consistent critical S level for corn and soybean production will help farmers and agronomists gain confidence in making S recommendations for their cropping systems as atmospheric S depositions decline.