In 1995, a long-term research trial was established at the Northwestern Illinois Ag R&D Center (NWIARDC) to study the effects of crop rotation and tillage on corn, soybean and wheat yields and cropping system profitability. There are many factors that go into making the decision about which row crops to grow in a particular region: soil types, growing region and climate, grain prices and the demand and market infrastructure at local grain elevators. The decision about whether or not to till the soil sometimes seems to be less about hard data and more about personal philosophy or habit.
There are many reasons why the crop grown the previous year may affect the current crop's growth and development: the impact of crop residue on the physical growing environment (soil temperature and moisture, seed to soil contact, etc.), the build-up of pest or pathogen population, the effect of root architecture on nutrient mining and more. One might also imagine that tillage might be able to aid in the breakdown of residue, which while potentially having a negative impact on soil organic matter, soil structure and other 'soil health' properties, might positively affect seed to soil contact, spring soil temperatures and pathogen survival.
While this NWIARDC experiment has continued through 2016, in 2014 a summary of the results up to that point was written. The data showed that cropping sequence affected corn yield, with the highest yields in the soy-wheat-corn rotation, followed by the wheat-soy-corn, and the soy-corn rotations (Figure). Continuous corn production paid a steep yield penalty in this experiment, yielding poorly when compared to rotated corn. When compared to no-till, tillage increased corn yields by between 5 and 18 bushels per acre in the continuous corn, soybean-corn and soybean-wheat-corn rotations (Figure).
Similar to the corn yield results, soybean yields were significantly impacted by cropping sequence with the highest yields in the 3-year rotations, followed by the traditional corn-soy rotation (Figure). Perhaps unsurprisingly, the very non-traditional continuous soybean was the poorest yielding cropping system. Unlike corn, soybean yields did not differ between tillage treatments in any of the four cropping systems.
From a dollars and cents standpoint, soybean prices in 2017 are projected to be $9.10 per bushel, and primary tillage is estimated to cost a minimum of $15.40 per acre, meaning that tillage should at least increase soybean yields by 1.7 bushels per acre in order to pay for itself. With cash rental rates remaining higher that the costs of production in many instances and fuel prices projected to increase in the coming months, any production practice or input that doesn't pay for itself most of the time should receive considerable scrutiny.
Schnitkey, G. 2015. Machinery Cost Estimates: Field Operations. Illinois Farm Management Handbook.
Schnitkey, G. September 2016. Crop Budgets, Illinois, 2017. Illinois Farm Management Handbook.