When farming the same land year after year, it is important to understand crop succession and the carryover effects that plants contribute to the soil for future crops.
Some of the well known benefits are nitrogen fixation and nutrient retention. If we focus only on these benefits we miss some other critical pieces. There can be many potential crop carryover effects, ranging from improved soil aggregation to improved trace mineral availability.
We expect a yield increase when we plant corn after soybeans, which we attribute to nitrogen carryover from the prior legume crop.
But why is there a yield bump on soybeans planted after corn?
Why is wheat resistant to take-all for multiple seasons after a single planting of oats?
Both corn and oats produce a strongly reduced environment in the rhizosphere surrounding their root systems; oats very aggressively so.
In this environment, trace minerals, particularly manganese, are converted to the reduced form (Mn+++) which is the form plants can utilize very readily. Manganese in the oxidized state (Mn++) is not bioavailable, and does not contribute to plant health and immunity.
When soybeans are planted after corn, they benefit from the reduced soil environment generated by the corn root system, and have access to better manganese nutrition, resulting in improved reproduction and better yields.
When successive wheat crops are planted after a single planting of oats, they have access to higher levels of manganese and other trace elements, resulting in improved resistance to take-all.