Linking soil health indicators to management history and soybean yield

Many soil health tests quantify some portion of soil organic matter, through both extractions and incubations. Four such tests have been identified as potentially useful measurements for farmers to track soil health on their farm, alongside typical routine soil testing: permanganate oxidizable carbon (POXC), mineralizable carbon (Min C), potentially mineralizable nitrogen (PMN), and autoclaved citrate extractable protein (ACE-N). These indicators have been related to crop yield, but not for soybean productivity. Our study relied on soil samples (0–15 cm) and field history data from 323 producer-managed soybean fields throughout Wisconsin between 2019 and 2021. Our first objective was to explore the impact of management history and inherent soil factors like texture and drainage class on soil health indicator values. Both conditional inference trees and random forest analysis were used to explore these relationships. Inherent factors like texture class and drainage class were important for determining capacity of a soil to achieve high soil health values. Some management factors were important as well, such as crop rotation (for POXC) and manure use (for ACE-N and PMN). Our second objective was to explore the relationship of these four soil health indicators and soybean seed yield using the same analyses. The conditional inference tree explaining soybean yield only showed soil order as a consistent predictor of yield. Random forest analysis showed latitude was the most important factor for soybean yield, followed by POXC. Further analysis showed a positive relationship between POXC and soybean yield (p < 0.001; Adj. R2 = 0.16). This exploratory study underlines the need for regional benchmarks beyond texture class for these soil health indicators, including factors like drainage class, soil order, and location. The positive relationship between soybean yield and POXC provides a quantifiable goal, which may support soybean farmers in prioritizing soil health.