One of the famous example of natural control of plant disease, Take All disease Wheat caused by Gaeumannomyces graminis var. tritici through monocropping.
Is the similar kind of thing happen in the case of soybean.
From my experience in North America maize and soybean cropping the maize after maize or the soybean soybean systems do less than a cereal legume rotation. The ability of maize to be high yielding is about 18% higher in the maize after soybean compared to maize after maize. In soybean after maize the increase of soybean is about half of the 18% because unlike maize which gets a Nitrogen response the soybean response is strictly related to soilborne pathogens. One of the most effect ways of increasing wheat production is the planting of oats before the rotation to wheat. The pathogenicity of take is related to take all ability to oxidize Manganese putting the plant into a susceptible state from Manganese deficiency. Apparently oats stimulates a soil microflora which mobilizes the Manganese making the virulence of take all from its Manganese oxidizing capacity not so critical. The oat wheat forage soybean maize rotation with winter cover crops is very effective in building soils and improving plant health and yield including counteracting the greenhouse gases of input practices and improving environmental and economic results.