Does Soil Organic Matter Matter for Crop Productivity?

Soil Organic Matter (SOM) is considered a vital component in soil-based agriculture. It is often used as an indicator of soil health and good soil management and is considered a prerequisite for sustainable plant productivity. However, these conclusions are not unequivocally borne out by evidence, especially from long-term field experiments such as the Magruder plots in Oklahoma, USA, where after more than 130 years of continuous wheat production without any fertilization, yields of 1 t/ha have been produced while soil organic matter declined from 4% to 1%. Furthermore, yields from soil-less production in advanced greenhouses have exceeded 600 t/ha/yr for tomato and up to 1000 t/ha/yr, compared to soil-based yields under 200 t/ha/yr. This is further evidence that soil and its various components are not prerequisites for high yields and maximal plant productivity. This narrative review will critically focus on the fate and role of SOM in crop production systems. The types of SOM, the effects of components such as humic materials, waxes, and organic amendments like composts, and the implications for soil health and the roles of soil microorganisms will be discussed. Physical properties of soils and agronomic practices, such as no-till, will be discussed in relation to SOM, and comparisons with soilless production will be evaluated to elucidate the role of SOM in crop productivity.