Positive associations of soil organic matter and crop yields across a regional network of working farms

The amount of soil organic matter (SOM) is considered a key indicator of soil properties associated with higher fertility. Despite the ubiquity of assumptions surrounding SOM’s contributions to soil functioning, we lack quantitative relationships between SOM and yield outcomes on working farms. We quantified the relationship between SOM and yields of corn (Zea mays L.) and silage for a dataset of 170 fields arrayed across 49 farms in a network of growers based in Wisconsin and Minnesota, USA. As SOM concentrations increase, so do yields, though gains start to level off around 4% SOM. When examining the relationship between yield and soil health indicators representative of biologically active carbon pools, we found that mineralizable carbon (min-C) has a stronger relationship with yield than permanganate oxidizable C (POXC). Mineral fertilizer, manure, and SOM had relationships of similar magnitude with yield, highlighting that SOM in combination with exogenous inputs likely plays an im...