Numerous studies have documented yield reductions when corn follows corn rather than soybeans, even when all yield-limiting factors appear to have been adequately addressed.
Better understanding of factors that limit continuous corn yield can help improve management of this production system.
A recent study at the University of Illinois compared CC and corn following soybean (CS) yields over a 6-year period. With the exception of nitrogen fertilizer rates, which were varied as part of the study, high-yield management practices were applied uniformly to both CC and CS systems - this included the use of soil-applied insecticides for rootworm control. In general agreement with previous research, the Illinois study reported a significant yield penalty and generally higher N fertilizer requirement for CC compared to CS. On average over 6 years, CC yielded 25 bu/acre less than CS and required 10 lbs/acre more N fertilizer to achieve optimum (but lower than CS) yields.
The authors of the study used their field data to develop a regression model that identified the most important combination of factors contributing to reduced yields in the CC system. Of 11 potential yield-limiting factors that were evaluated, 2 factors were identified that, when taken together, explained more than 97% of the difference between CC and CS yields: soil N supply and CC history of the field.
N supply was by far the most important factor explaining the difference between CC and CS yields. Overall, the ability of soil to supply N explained 85% of the CC yield penalty. Soils with higher N mineralization capacity supported higher CC yields, as was evidenced by a negative relationship between unfertilized (0-N) corn yield and the CC yield penalty. Soil N mineralization is reduced in CC systems due to the slower rate at which corn residues break down and release N relative to soybean residues. Soils also tend to warm more slowly in the spring when the previous crop was corn, which reduces activity of soil bacteria responsible for N mineralization. The fact that the CC yield penalty was smallest where relatively high corn yields were achieved, even in the absence of N fertilizer, shows that soils with high intrinsic N supply capacity are generally best suited for CC.
CC history was identified as the second most critical component of the CC yield penalty. Soil N supply and CC history together explained 97% of the difference between CC and CS yields. While many growers report that their CC yields approach CS yields over time, this study found that the CC yield penalty increased with years in CC.
While producers typically alter management as they gain experience with CC, management remained relatively constant over time in the Illinois study. Therefore, CC history in this study likely reflects the underlying effects of excessive corn residues accumulating in and on the soil over time in the CC system. Corn residues exert negative effects on nutrient cycling, early season soil temperature and moisture, and increased disease pressure for subsequent corn crops.
Source: University of Illinois and DuPont Pioneer